rol and significance of enzymes in human milk

8/12/2019 Rol and Significance of Enzymes in Human Milk

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Th e Am erican Journa lo fC lin ica l N u tr itio n 33 : A U GU ST 1980 p p. 1861 1868. Printed in U .S.A. I 861

o le nd s ign ific nce o f enzym es in hum n

K . M . Sha ha n i A . J . K w an an d B everly A . F riend

A B S T R A C T A lthou gh hum an m ilk gen era lly con tain s h ig her le vels of enz ym es th an b ov inem ilk , li ttle def in it ive in form a tion is av aila b le c onc ern ing th eir ro le or sig n if ica nce . T he en zy m ele ve ls in hu m a n m ilk a s c om pa red to bo vin e m ilk a nd lev els in hu m a n colo strum v ersus no rm a lm ilk a re sum m ariz ed . T h e few m ost w id ely stud ied h um an m ilk enz ym es are d iscu sse d in m ored eta il. E v ide nce is p resen ted to sup po rt the v iew s that lip opro te in lip ase a nd r ibo nuc lea se a rep rob ab ly sp illed in to the m ilk f rom th e b loo d; 2 ly soz ym e is sp i lled fro m the sec reto ry ep ithe lia lcel ls; 3 la cta te a nd m a late deh ydroge na ses, g lu cose-6 -ph osp hate d ehy dro gen ase, an d lacto sesyn thetase are sy n th esiz ed in th e m a m m ary gland in resp on se to ho rm o na l stim u li; an d 4 bile salts tim ula ted lipa se , d ias tase , p ro te ase , an d lysozy m e are p resen t in su ffic ien t qu an titie s to aid in fa n tsin g row th a nd n utr itio n . C on sid era tion m u st be g iv en to s tan dard izing the va riou s e nzy m e assa yp roc edu res an d a ctiv ity un its so that m ea nin gfu l c om par iso ns be tw e en va riou s stu d ie s c ou ld bem a d e . A m . I C lin . N u tr. 33 : 18 61 -18 68 , 1 980 .

H um an m ilk is ph ysio log ica lly adap ted fo rthe p rom o tion of h ealth an d nu trition in then ew b orn in fan t. In con tra st to p ro cessedco w s m ilk , hu m an m ilk is a live sec re tionco n ta in ing ac tive enzym es, ho rm o nes and es-s en tial nu tr ien ts p re sum ab ly in the p rop erfo rm s an d p ro portions fo r the in fan t. A l-th ou gh hum an m ilk gen era lly co n ta ins con-side rab ly h ighe r leve ls o f en zym es than bo-v ine m ilk , little d efin itive in fo rm a tion isav ailab le con ce rn ing the ir ro le o r sign if i-can ce .

S hahan i e t al. 1 ) rev iew ed th e en zy m es inb ov ine m ilk and su ggested tha t they a re p rob -ab ly norm a l con stituen ts o f th e sec re to ry ep -ith elia l cells w he re th ey pa rtic ipa te in cellm e tab o lism and th e b iosyn thesis o f m ilk con -s tituen ts . D uring th e m ilk ing pro cess the ce llsrup tu re and sp ill the enzym es in to the m ilk .In ad d ition , som e enzy m es m ay be sec retedd irec tly in to th e m ilk to bene fit th e new bornin fan ts w h o h av e incom p lete d igestive sy s-tem s. T h e curren t pape r w ill rev iew th e p hys-io log ica l s ign ificance o f so m e h um an m ilkenzym es an d w ill p re sen t ev idence th at the seenzym es pe rfo rm ro le s sim ila r to tho se sug -gested fo r th e b ov ine sys tem .

T able sho w s th e re la tiv e co ncen tra tion ofenzym es in hu m an m ilk as co m pared to bo-v in e m ilk . T he n um b er in pa ren thesis re fe rsto th e enzym e c las sifica tion num bers sug -

gested b y the C om m ittee on E n zy m es of theIn te rn atio na l U n ion o f B io ch em istry 2 ). B yand la rg e, th e leve ls o f va rious enzym es a reh ig he r in hum an m ilk than tho se in bo v inem ilk . In fo rm a tion o n th e m ore sig n ifican ten zy m es w ill be p re sen ted la te r.

A s show n in T ab le 2 , the stage o f lac ta tionsig n ifican tly a ffec ts the co ncen tra tio n of en -zy m es in hum an m ilk . In g en e ra l, th e m ajo r-ity o f the en zy m es a re p resen t in sig n if ican tlyh igh er con cen tra tion s soon a fter p artu r itionand gradua lly dec line the rea f ter . In ad d ition ,the m ann er and fo rm of nu tr ien t in take bylacta ting w om en as w ell a s the tim e of sam -p ling m ay also in fluen ce the leve ls o fthe m ilken zy m es .

In a stu dy w ith 60 lac ta ting w om en , K ar-m ark er an d R am ak rish nan 3 ) fo und tha td ie ta ry fa t in take up to 7 2 g /d ay in creasedthe lev els o f lip ase , e ste ra se , an d a lka lin epho sph ata se bu t dec reased ac id p hospha ta se .In a la te r stud y , they con clu ded tha t lipa se ,e ste ra se and a lka line p hospha ta se p lay a ro lein the d igestio n , as sim ila tion , and m e tabo lismof fat, bu t are no t in flu en ced by pro te in and

F rom the D epa rtm en t o f F oo d S cien ce a nd T ec h-n o lo gy , U niversity of N eb raska, L in co ln , N ebra sk a68583.

2 P u blishe d as P ape r n o . 57 51 , Jo urn al S er ies , N e -b raska A g ricu ltu ral E xpe rim ent S tation . R esearch re-p or ted w a s c ond uc ted un der P ro je ct no . 1 6-026 .


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1862 S H A H A N I E T A L .TABLE 1E nz y m e lev e ls in h um an m ilk v ers us bov ine m ilk

R e l a t i v eE n z y m e

H u m an m ilk

c o n t e n tR e f e r e n c e

B ov in e m ilk2 3x (3 9)de nos ine trip hos ph atas e

(3 .6 .1 .3 )( A T P p ho sp ho h yd ro la se )A lan ine am ino tran sf erase 4 00x (2 1)(2 .6 .1 .2 )(L -A lan ine : 2 o x o g lu tarate am ino transf e ras e)

A l d o l a s e 5x (21 )(4 . 1 .2 . 13 )(Fru cto se-l ,6 d iph osp hate D -g ly cerald ehy de -3 -p ho sph ate ly ase)

a-A m y lase (d iastase) 2 5x (8 )(3 .2 .1 .1 )( a-1 ,4 -G lu can 4 -g lu can oh yd ro las e)

18 -A m y lase 4 0x (2 1) 3 . 2 . 1 . 2(a-1 ,4 -G lu can m alto hy dro las e)A rylesterase 4x (39 )(3 .1 .1 .2 )A ryl-e ste r hydrola seA sp artate am ino transf erase lO x (2 1)(2 .6 .1 .1 )(L -A sp artate: 2 o x o g lu tarate am in o transf erase)

Ca t a l a s e lO x (3 9 )(1 .11 .1 .6 )(H y d ro gen -pe rox ide : hy dro gen pe rox ide o x id ore duc tas e)

C ho line ste ras e 9 -l6 x (3 9)(3 .1 .1 .8 )(A cy lc ho l ine acy l-h ydro lase)

G luc ose ph osp hate iso m e rase 2 x (2 1)(5 .3 .1 .9 )(D -G lu cos e-6 -ph osp hate k eto l-is om eras e)

- G lu curon idas e 2 0-3 0x (4 9)(3 .2 .1 .31 )( /J-D -G luc urO nid e g luc uro noh yd ro lase)

I no rg an ic p yro ph os ph atas e (39 )(3 .6 .1 .1 )(Py rop ho sph ate p ho sph ohy dro las e)

L actate deh y droge nase 3 .5x (5 , 1 8 )(1 .1 .1 .27 )(L -L ac tate: N A D o x id ore duc tas e)

L actose sy n th e tase lO x (14) 2 . 4 . 1 . 2 2( U D P g alac to se : D -g lu co se , I- gal ac to sy ltran sf eras e)L ipase 8 - lO x (16 , 50 )(3 .1 .1 .3 )(G ly ce ro l-ester hy dro lase )

a T he en z y m e re ported as d iastase is m os t lik e ly a-am y lase b u t m ay also con tain som e -am y lase .


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E N Z Y M E S IN H U M A N M IL K 1863T A B L E 1 (C o n tin u ed )

E n z y m eR elativ e co nte nt

R e f e r e n c eH u m an m ilk B o v in e m ilk

L y s o z y m e(3 .2 .1 .17 )(M u co pe ptid e N -ac et ylm u ram y th yd ro las e)

3000x (33)

M alate d eh yd ro ge nas e(1 .1 .1 .37 )(L -M alate N A D o x id ore du ctas e)

l-5 x (5 , 18 )

Peroxidase(1 .11 .1 .7 )(D on or: h y d rog en-perox ide ox idoredu ctase)

lO O x 3 9 , 51

Phos phatas e , ac id(3 . 1 .3 . 16 )(Pho sph op ro te in ph osp hoh yd ro lase)

S am e (21 )

Phos phatas e , alk aline(3 .1 .3 .1 )(O rthop ho sph oric m onoe ste r p hos ph ohy dro las e)

40 x (21 , 3 8 )

Pro tease(3 .4 .4 - )(Pe p tidy l pe p tid e h y dro lase)

5 x (3 9 , 40 )

Ribonuclease(4 .7 .7 .16 )( R ib o nu c le at e p y ri m i di ne -n u cl eo ti de -2 - tr an s fe ra se )

3 .5x (4 2 , 43 )

X an th in e o x id ase(1 .2 .3 .2 )(X a n th in e : o xy ge n o xid ore du ct as e)

lO x (5 ,46 -48)

v itam in su pp lem en tation (3 A ). S k lav un u-Z u -ru k z og lu e t al. (4 ) reported the adm in istratio no f v itam ins A , B 6 , B 12 , C , and K to lac tatingw om en d id n o t h av e any in f lu ence on th elev e l o f g lu cose -6 -p hosp hate dehy drogenase .S im ilarly , D eod har e t al. 5 demonstra tedd aily v itam in in tak e had no e f f ec t on x an-th in e ox idase , lac tic ac id d eh y drog en ase, andm alic ac id d eh y drog en ase ac tiv itie s in h um anm ilk . B e lav ady (6 , 7 ) , ho w ev er, no ted thatp ro tein sup p lem en tation f o r th ree to f o urw eek s in creased alk alin e pho sph atase (6 ) andx an th in e o x id ase (6 , 7 ). T he f o llow ing repre-sen t the m o st w ide ly stud ied enz y m es o f hu -m an m ilk .Diastase

D iastase cataly z es the hy dro ly sis o f s tarchto m alto se, an d , theref ore , is m ost lik e ly theen z y m e a-am y lase bu t m ay re f e r to a m ix tureo f a an d am y lases. H anaf y e t al. (8 ) no teda sharp in crease in th e lev el o f d iastase in

co lostrum at the m idd le o f p regn ancy , a rap idf all d uring th e f irst 6 m o nths o f lac tation ,f o llow ed b y a g radu al declin e u n til a con stan tlev e l w as reach ed at 6 m on ths. T hese au thorssugg ested that the d iastase in th e m ilk m ayb e bene f icial to n ew bo rn in f an ts w ho arede f ic ien t in pancreatic d iastase . T h is w ou ldalso ex p lain the c li cally ob serv ed lack o fd igestiv e d isturbances in breast- f ed in f an tso f f e red starch f orm u la early -a situ atio nw h ich o ccu rs particu larly in po or c lasses.G lu co se -6 -ph osp hate dehy d ro genase

G lu cose -6 -p hosp hate d eh y drog en ase cata-ly z e s the o x idation o f g lucose -6 -pho sphate(2 ) . S k lav un u-Z u ruk z og lu e t al. (4 ) stu d ied1 7 nursing m o th ers w ith no rm al red ce ll g lu -

co se -6 -ph osp hate d eh y drog en ase and f oun dthe ir m ilk rich in th e enz y m e. T w o m o thersw ith com p lete absen ce o f th e enz y m e in redce lls also h ad com p lete ab sence o f the enz y m ein the m ilk . S in ce the large quan tity o f g lu -


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1 8 6 4 SH A H A N I E T A L .T A B L E 2E n zy m e le vels in h um an m ilk c o lo stru mv ersu s no rm al m ilk

E n z y me N o rma lC o l o s t ru m mi l k R e fe re n c e

A den osine tr iph osp ha - 39 )tase

A lan ine a m in o tra nsfer- 2x 2 1)as e

A l d o l a s e 2 1a-A m yla se d ia sta se) 8)fJ-Amylase 1 .5 x 2 1)A spa rta te a m inotran s- 2x 2 1)

feraseCa t a l a s e 2 x 3 9)Cholinesterase 39 )G luc ose -6-pho sph ate N o c han ge 4 )

dehydrogenaseG luc ose -ph osp ha te l.5 x 2 1)

i s o me r a s eIno rga nic p yro ph osp ha- 39 )

taseL ac tic d eh yd ro ge na se 5 , 1 8)Lipase 2 1L y so z y m e 47 )L y soz ym e N o c han ge 3 3)M alic de hyd rog en ase + 5 , 18)Perox idase 3 9 , 51)P h osp ha tase , acid 3x 2 1)P h osp ha tase , a lk alin e 4x 2 1)Pro tease 2x 39)X an th ine ox ida se 5 , 46 ,

4 7a h e e nzy m e repo rte d a s d ias tase is m o st l ike ly

am ylase bu t m ay a lso c on tain som e fl-a m y lase .

co se -6 -ph osph a te dehy drogenase in the m ilkis re la ted to the inc rea sed ra te o f carbo hy-d ra te m e tabo lism in the m am m ary g lan d du r-in g lacta tion , the se au tho rs sug gested th a t theg rea t va ria tion o f g lucose -6 -pho spha te dehy -d ro genase fo und in th e sam e ind iv idu al isdue to the sam e neuroh orm ona l in f luencew h ich regu la te s the p rod uc tion an d sec re tio no f m iL k .L ac tose syn the ta se

L ac tose sy n the ta se , an enzym e presen t inth e m am m ary g land and in m ilk , cata lyzesth e sy n thesis o f lac tose from urid ine d ip hos -p ha te U D P ) ga lacto se an d g lucose 2 8 ). T helac tose syn th e tase enzym e h as tw o com p o-n en ts-an A p ro te in w h ich is a g lycopro te inco n ta in ing hexose, hexosam in e and sia lic ac id 9 , 10 ) and a B pro te in w hich is th e m ilkp ro tein a - lac ta lbum in 9 , 1 1 ) . S epa ra ted Ap ro tein ac ts a s a ga lacto sy l transfe ra se in the

co nve rsion of U D P g alac tose and N -ace ty l-g lucosam in e to N -ace ty llac tosam ine andU D P . In the p re sence of a -lac ta lbum in , thela tte r reac tion is p artia lly inh ib ited and lac -to se fo rm a tion is fav ored 9 , 1 2 ) .A n drew s 1 3 ) sho w ed th at a- lacta lbu m in ,in the p resen ce of g lucose at no rm a l tissuecon cen tra tion , ac ts a s a com p etitiv e in h ib ito ro f th e A p ro tein ca ta ly zed syn th esis o f the N -acety llac tosam ine . In ano th er study A ndrew s 14) fou nd tha t the A pro te in d oes p osse sss ligh t lac tose syn th eta se ac tiv ity ev en in theabsence of a -lac talb um in .

F itzge rald et a l. 15 ) su ggested tha t a - lac t-a lbu m in lo w ers the K m of g lu co se so tha t itc an b e u sed m ax im a lly in lac to se b iosyn-thesis . A ndrew s 1 4 ) ob served in a c ru deprepa ra tion o f the A p ro tein from hu m anm ilk th at th e Km fo r g lu co se w as low eredfro m 6 0 m M in the absence to 3 m in th ep re sence o f a- lacta lb um in . K lee and K lee 16 ) repo rted in the p resen ce of a - lac ta lbu -nu n , the norm a l in v ivo co ncen tra tion ofg lucose is op tim a l fo r lac tose syn th es is .

B rew e t a l. 12 ) fo und tha t a s th e m am m aryg lan d deve loped d uring preg nancy , th e co n-cen tra tio n of A pro te in and , to a le sse r ex ten tthe con cen tra tion o fa - lac ta lbum in , inc rea sedw ith tim e. A t pa rtu ritio n , h ow ev er , w h en lac -ta tion com m en ced , the lev el o f a -lac ta lbum ininc reased sign ifican tly and prov ided thep rop er cond itions fo r lac tose syn th esis . T u r-k in g ton et a l. 17 ) fu r the r ob se rv ed tha t thep ro lac tin ind uced syn th es is o f A pro te in an da -lac ta lbum in in m ou se m am m ary g land ce llcu ltu re s occu rs sp ec if ica lly in d au gh te r cellsfo rm ed in th e p re sence of insu lin an d h ydro -co rtisone . T h is con tro l m ech an ism fo r lacto seb io syn th es is by th e A pro te in and c t- lac ta l-bu m in insu re s tha t lac tose is syn th esized on lyin th e m am m ary g land in re spo nse to sp ec if ich o r m o n es .L ac tic and m a lic ac id dehy drogenases

K jellb e rg and K arisson 1 8 ) foun d th at theactiv ity o f lac tic dehyd ro genase in hum anm ilk is h ig h in co los tru m , low er in m a tu rem ilk , and h ig hest a t the end o f lac ta tion .T hey a lso n o ted an inv erse rela tion sh ip b e-tw een b ody size o f a p a rticu la r specie s andlac tic d eh ydrog en ase ac tiv ity in m ilk . T hus,the h ig hest lac tic d ehyd rog enase ac tiv ity w asdem o nstrated in th e m ouse , fo llow ed b y m an ,


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E N Z Y M E S IN H U M A N M IL K 1865an d then th e co w . T he ac tiv ity o f m alic de -h y drog en ase show s the sam e p rinc ipal v ari-ation s during lac tation and app ears to ex istin a sim ilar in v erse re lationsh ip w ith b odyw e igh t as sho w n by lac tic dehy d ro genase .T h is is ex pec ted sin ce m e tabo lic rate s arek now n to be h igh er in cells f ro m sm all an i-m als than larg e. T h ese au tho rs also d em on-s trated th at alth oug h the lac tic an d m alicdehy d ro genase isoz y m es in m ilk show char-ac te ristic e lectrop hore tic patte rn s at d if f eren tstag es o f lactation , the b loo d seru m patternsshow no such v ariation . T hese resu lts su ggestth at lac tic d eh y drog en ase an d m alic dehy dro-genase are sy n th esiz ed in th e m am m ary g landrather th an transp orted f ro m the b loodstream an d that lac tic an d m alic dehy drogen-ase lev e ls in the m ilk o f v arious specie s p ro b-ab ly re f lec t m am m ary g land m e tab o lism .L ipase

L ipase cataly z es th e h y dro ly sis o f g ly cero le ste rs (f ats an d o ils) in em ulsio n (1 ). H erne lland O liv ecrona (19 , 20 ) h av e iso lated a serumstim u lated lipo pro te in lip ase f rom the creamand a b ile salt s tim u lated lip ase f rom th e sk impo rtion o f hum an m ilk . T h e serum stim ulatedlipase has n o app aren t p hy sio log ical f un ctio nin th e m ilk and pro bab ly resu lts f rom m am -m ary g land leak age (19) .

T he b ile salt s tim u lated lipase is presen t inm u ch h ig her activ ity than the serum stim u-lated lip ase (19) and has b een sho w n to re -sem b le pancreatic lipase (21) . In bov ine m ilk ,the b ile salt s tim u lated lipase ap pears to b epan creatic in o rig in and is transp orted to th em am m ary g land to partic ipate in th e sy n the -sis o f m ilk f at (22) .

T h e b ile salt s tim u lated lipase in hum anm ilk , h ow ev er, app ears to p lay a sign if ican tro le in the d igestion o f m ilk triacy lg ly cero lsin the in te stine o f in f an ts f ed hu m an m ilk(23 , 2 4) . It h as su f f ic ien t activ ity at lo w pHand at in testin al b ile salt co ncen tration s toau gm en t th e lo w lev e ls o f lip id reso rp tion inthe new born (25 ). T h is is particu larly im p or-tan t sin ce f ree f atty ac ids are an im p ortan tenerg y so urce f or the in f an t (26 ).

It is in tere sting to n o te th at hum an m ilklipases, in con trast to b ov in e m ilk , m ay beactiv ated at ref rig erated tem peratures. Forth is reason T arassu k et al. (27 ) reco m m end edpasteuriz atio n o f hum an m ilk in tend ed f or

sto rage in order to prev en t hy d ro ly tic ranc id -i ty .L y s o z y m e

L y soz y m e cataly z es the h y dro ly sis o f (-1 ,4 -) lin k age be tw een N -ace ty lg lucosam in ean d N -ace ty lm u ram ic ac id in th e bac te rialce ll w all (3 0). T he enz y m e ly ses m ostly grampositiv e and a f ew gram negativ e b ac te riaan d has b een pos tu lated to p lay a ro le in theinheren t an tibacte rial activ ity o f m ilk (31 ).

In 193 1 , R osen th al an d L ieberm an (3 2)dem o nstrated that hum an m ilk ly soz y m ep lay s a sign if ican t ro le in the dev e lop m en t o fthe in te stin al f lora o f breas t-f ed in f an ts . U n-lik e the m ix ed in te stinal f lora in in f an ts o ncow s m ilk , there is a prev alence o f Lactoba-cillus b idus in th e in testin e o f healthy breast-f ed in f an ts (26 ). C han dan et al. (33 ) reportedth at th e ly so z y m e co n ten t o f h um an m ilk isab ou t 3 00 0 tim es greate r than th at in bo v inem i l k .

Iso latio n and charac te riz ation o f the h u-m an m ilk ly so z y m e rev ealed a M W o f 15 ,00 0an d an ac tiv ity 3 .5 tim es that o f egg w hitely soz y m e and 100 tim es that o f b ov in e m ilkly so z y m e (3 4). T h is low lev e l o f ly soz y m eactiv ity in b ov in e m ilk and ab sence in p re -pared in f an t f orm u las (29) m ay represen t asig n if ican t prob lem in n u trition o f in f an ts f edthese p ro duc ts as th eir so le d ie t (35 ).

E itenm ille r e t al. (3 6 ) d ete rm ined that thehu m an m ilk ly soz y m e is an tigen ically an dsero log ically d if f e ren t f rom the bov ine en-z y m e . H y slop et al. (3 7 ) o bserv ed that there latio nsh ip be tw een ly soz y m e and to tal p ro -te in con ten t rem ains relativ e ly cons tan t inb o th co lo stru m an d m ilk . S ince ly so z y m e d idno t increase w ith th e increase in to tal m ilksecre tion af ter p arturition , these au tho rs sug-gested that the ap pearance o f ly soz y m e inm ilk m ay be co nsidered a sp illo v er p rod uc tf rom the b reast ep ithe lial cells .

Phospha tasesA c id p hosp hatase, w h ich is no t a ph osp ho-

m ono este rase (1 ) , has practically th e sam eac tiv ity in b o th h um an an d bov ine m ilk (21) .T he p hospho m on oeste rase alk aline pho sph a-tase , ho w ev er, h as an ac tiv ity in hu m an m ilkw hich is 4 0 tim es low er than that in b ov in em ilk (21 ).


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1866 S H A H A N I E T A L .S tew art et al. (3 8 ) de te rm ined that the al-

k aline pho sphatase co ncen tration appears tob e related to the f at co ncen tration in h um anm ilk . K arm ark ar and R am ak rishn an (3) alsod e term ined that alk aline ph osp hatase ac tiv ityin creases w ith an increase in f at concen tra-tio n , w h ile ac id pho sph atase do es no t. S tew -art et al. (38 ) also f oun d no co rre latio n be -tw een e ither n itrogen co n ten t or to tal so lidso ther than f at and alk aline pho sph atase ac -tiv ity . T hese au tho rs d id no te a tenden cy f o ralk aline ph osph atase to increase as lac tationprogressed , w h ile H ey n drick x (21) repo rteda f ou rf o ld low er ac tiv ity in no rm al m ilk thanco lostrum.Protease

Pro tease cataly z es the h y dro ly sis o f p ro -te ins (2 ). S in ce there are h igher lev e ls o fpro teo ly tic enz y m es in h um an m ilk com p aredto cow s m ilk (39 , 4 0) , S torrs and H ull (40)su ggested that these enz y m es m ay p ro v idethe b reast-f ed in f an t w ith sign if ican t d ig es tiv eassistance im m ediately af te r b irth . S tu d ie s b yE ig el (41) in d icate th at in bo v ine m ilk p las-m m is th e pro tease resp ons ib le f or in v iv oprodu c tion o f m inor case in f ractio ns. H ow -ev er, n o such pro tease or p lasm in has b eenrep orted f o r h um an m ilk .R ibonuc lease

R ib onu clease cataly z es the hy dro ly s is o frib onu c leic ac id (1 ). B ingh am and Z ittle (42 )iso lated and ch aracte riz ed rib onu clease Af rom b ov in e m ilk and f o und it to b e id en ticalto b ov in e pancreatic ribo nu clease A w ith re-spec t to am ino ac id com p osition , e lec trop ho-re tic b eh av ior and im m uno log ical prop ertie s . h s au thors sugg es ted that p an creatic ri-bo nuc lease en ters th e m ilk v ia the b lo odstream . D alaly e t al. (43 ) purif ied hum anm ilk ribon uc lease and f ou nd it p ossesses anabso lu te sp ecif ic ity tow ard p y rim id in e andrib ose m oie tie s . In th is resp ec t, it appears toresem b le the bo v ine pancreatic ribon uc leaseA . H ow ev er, the h um an m ilk ribon uc leased if f e rs co nsid erab ly f ro m th e b ov in e enz y m ein am ino ac id co m po sition .X an th ine o x idase

X an th ine o x idase cataly z es the ox id atio no f purines, py nm id ines an d ald eh y des (1 ) . In

1 946 , R o dk ey and B all (4 4) reported thath um an m ilk is dev o id o f x an th ine ox id ase,w h ile cow s m ilk is rich in th is en z y m e , ev enaf te r co m m erc ial pasteuriz ation . T hese au -tho rs sugg ested that the x an th in e ox idase ac -tiv ity m ay be used to d is tingu ish hu m an m ilkan d cow s m ilk and , in particu lar, cou ld b eused to te st f or th e d ilu tio n o f h um an m ilksam ples w ith cow s m ilk . O w en an d cow o rk -ers (45 ) also reported th at x an th in e o x idase isabsen t in hum an m ilk . H ow ev er, in 196 0 ,B rad ley and G unth er (4 6) , u sing a m ore sen-s itiv e assay techn iq ue , f oun d sm all am ou n tso f x an th in e ox id ase in h um an m ilk . O n th eb asis o f these f m din gs, O w en and H y tten (4 7)reex am ined hu m an m ilk sam ples and f oun dx an th ine ox id ase . T he activ ity o f x an th in eox idase peak s o n the 3rd day af te r b irth andd ecreases w ith the prog ress o f lac tation (4 6 ,4 7) . Z ik ak is e t al. (4 8 ) also show ed th at h u-m an m ilk x an th ine ox id ase d if f e rs f rom bo -v ine m ilk x an th ine ox id ase and it is n o t o fb acte rial o rig in . A lth ou gh v itam in supp le-m en tation has no ef f ec t on the activ ity o fx an th in e ox id ase (5 ), the co ncen tration o fp ro te in can be co rre lated w ith x an th in e o x i-d ase ac tiv ity (6 , 7 ).

Conc lusionH um an m ilk is a h igh ly co m plex f lu id

con tain ing nu m ero us ac tiv e enz y m es. T h eseenz y m es in m ilk m ay serv e spec if ic f unc tion so r h av e no k now n ro le . H o w ev er, the en z y m eac tiv ity lev e ls in h um an m ilk are af f ected byf acto rs such as the sen sitiv ity o f the assay , th ed uratio n o f m ilk sam plin g , th e tim e o f lac ta-tio n f or sam p ling , an d v ariatio ns w ith in in -d iv idu als . A lso , th e sign if icance o f each en-z y m e in hum an m ilk as a re f lec tion o f then u tritio nal s tatu s o f the m oth er, its po ssib leo rig in , an d its n u tritiv e v alu e to the in f an t isno t abso lu te ly clear. B u t, ev id en ce has beenpresen ted to supp ort the v iew s th at in h um anm i l k 1 lip op ro te in lipase and rib onu cleaseare poss ib ly sp illed in to th e m ilk v ia the b loo dstream f rom th e pancreas; 2 ly soz y m e issp illed in to the m ilk f rom the secre tory ep i-the lial ce lls; 3 lac tate and m alate dehy d ro -genases, g lucose-6 -ph osph ate dehy drogenase ,and lac tose sy n the tase are sy n thesiz ed in them am m ary g land in resp onse to h orm onalstim u li during p regn an cy and lac tatio n ; and b ile salt s tim u lated lipase , d iastase , p ro -


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E N Z Y M E S IN H U M A N M IL K 1867tease , and ly so z y m e are presen t in hum anm ilk in sign if ican t qu an tities to aid new bo rnbreast- f ed in f an ts in the dev e lop m en t o f the irproper g ro w th , h ealth , and nu trition .

I t is also im portan t to no te that there is noun if orm ity am ong th e assay p ro ced ures, sub-strate s used or activ ity un its ex pres sed f or thesam e enz y m e reported b y d if f e ren t w ork ers.C on sideration m u st be g iv en to standard iz ingthese param e ters so th at activ ities repo rted b yv arious w o rk ers can be read ily com pared .C alcu lation o f spec if ic ac tiv itie s in te rm s o fm oles sub strate p er m inu te per stand ardam ou nt o f m ilk co u ld be o f v alue ; Re ferences

1. S H A H A N I, K . M ., W . J. H A R P E R , R . G . J E N S E N , R .M . PA R R Y , JR . A N D C . A . Z IT FL E . E nz y m e s in bo v in em ilk : a rev ie w . J. D airy S ci. 5 6 : 5 31 , 19 73 .2. F L O R K IN , M ., A N D S . H . E L M ER . R eport of theC o m m is sio n on E nz y m es o f the In te rnation al U n iono f B ioch em istry . C o m p ieh ens iv e B ioc he m is try . A m -ste rdam : E lse v ie r Pu bI. C o . , 19 64 , v o l. 13 .

3. K A R M A R K A R , M . G ., A N D C . V . R A M A K R I S H N A N .R e lat ion b etw een d ie tary f at , f at co n te n t o f m ilk an dc onc en tration o f ce rtain e nz y m e s in h um an m ilk . J.N u tr. 69 : 27 4 , 1 959 .

3A . K A R M A R K A R , M . G ., R . R A JA L A K S H M I A N D C . V .R A M A K R I S H N A N . S tu d ies o f h um an lactat ion . II . A c-tivities o f c ertain m ilk en z y m es in re lat ion to d ie taryf at in tak e . A cta Paed iat. 5 2 : 55 1 9 6 3 .

4. S K L A V U N U - Z U R U K Z O G L U , S . , C . M A M EL E T Z IS A N DD . K A T R I U . O bs erv atio ns on the g luc ose -6 -pho s-p hate deh y d rog enase o f th e breas t m ilk . H elv . Pae-d i a t A cta 2 0: 193 , 19 65 .

5. D E O D H A R , A . D ., R . R A JA L A K SH M I A N D C . V . R iM A K RISH NA N. Studies on hum an lactation. IV . Lact icand m alic deh y d rog enases and x an th ine ox idase inbre ast m ilk and th eir v ariatio n w ith the progress o flac tation an d d ie tary v itam in su pp lem en tatio n . A c taPae d iat. 53 : 101 , 19 64 .

6. B E L A V A D Y , B . X anth ine o x id ase and alk alin e pho s-ph atas e activ ity in the bre ast m ilk o f po or In d ianw o m e n . In d ian J. M ed . R e s. 48 : 65 4 , 19 60 .

7. B E L A V A D Y , B . E ff ec t o f p ro te in su pp lem en tatio n tonu rsin g m o the rs on som e m ilk c ons titu en ts: case inan d x an th ine ox idase . In d ian J. M ed . R es . 50 : 1 00 ,1 9 6 2 .

8. H A N A F Y , M ., S . E L -K H A T E E B , F. K . G UIR IS A N D M .E L -L o z Y . D iastase in h um an m ilk . A lex . M e d . J. 17 :29 9 , 1 971 .

9. B R O D B i U ., W . L . D E N T O N , N . T A N A H A SH I A N DK . E . E B N E R . T he iso lation an d id en t if ic ation o f theB p ro te in o f lac to se sy n th e tas e as a-lac talbu m in . J.B io l. C he m . 2 42: 1 391 , 196 7 .

10 . N A G A SA W A , T ., T . K IY O SA W A A N D N . T A N A H A S H I.Pu rif icat ion o f the A pro te in o f h um an m ilk lac tosesy n the tas e and ide n ti f icatio n as a g ly c opro te in . J.D airy S ci. 5 4 : 8 35 , 19 71 .

1 1. B R O D B E C K , U ., A N D K . E . E B N E R . R esolution of aso lub le lac tos e s y n the tase in to tw o pro te in com po -

nen ts an d so lu b il iz ation o f m icro som al lac tos e sy n -thetase. J. B io l. C h em . 2 4 1 : 7 6 2 , 1 9 6 6 .

12 . B R EW , K ., T . C . V A N A M AN A N D R . L . H I L L . T he roleo f a-lac talb um in an d th e A pro te in in lac tos e sy n -the tas e: a un ique m ech an ism f o r th e co n tro l o f ab io log ical reac tion . Pro c . N atl. A c ad . S c i. U .S .A . 5 9 :4 9 1 1 9 6 8

13 . A N D R E W S , P. Pu rif icat ion o f lac tose sy n the tas e Apro te in f rom h um an m ilk and dem on stratio n o f itsin teractio n w ith a-lac talbu m in . FE B S L ett. 9 : 2 9 7 ,1 9 7 0 .

14 . A N D R E W S , P. L ac to se sy n the tase A pro te in f ro mhu m an m ilk . B ioc hem . J. 1 1 1: 1 4P, 19 69 .

15 . F IT Z G E R A L D , D . K ., U . B R O D B E C K , I. K I Y 05 A w A , R .M A W A L, B . C O L V I N A N D K . E . E B N E R . a-L actalb u-m m an d th e lac tose sy n th e tase reac tio n . J. B io l. he m 2 45: 2 10 3 , 197 0 .

16 . K L E E , W . A ., A N D C . B . K L E E . T h e ro le o f a -l ac ta l-bu m in in lac tose s y n the tase . B ioc hem . B iop hy s . R es .C om m un . 39 : 83 3 , 1 970 .

17 . T U R K IN G T O N , R . W ., K . B R EW , T . C . V A N A M AN A N DR . L . HILL. T he h orm o nal c on tro l o f lac tos e sy n the -tase in the de v elop ing m ous e m am m ary g land . J.B io l. C h em . 2 43: 338 2 , 1 968 .

18 . K J E L L B E R G , B ., A N D B . W . K A R L SSO N . C om p arativeanaly s es o f lac tic and m alic d ehy dro ge nas es an dthe ir m u ltip le m o lec u lar f orm s in m ilk f ro m v ariou san im al spe cie s and m an . C o m p. B io ch em . Ph y sio l.22 : 39 7 , 1 967 .

19 . H E R N E L L , 0. , A N D T . O LIV E C R O NA . H um an m i l klipases. I . S e ru m - s ti m u la te d l ipase . J. L ip id R es. 1 5 :367 , 19 74 .

20 . IE R N E L L , 0. , A N D T . O LIV E C R O NA . H um an m i l klipases . I I. B ile salt-s tim u lated lipas e . B io ch im . B io -phys. A cta 3 69: 23 4 , 19 74 .

21 . U E Y N D R IC K .X , G . V . Inv est igatio ns on th e en z y m e sin h um an m ilk . A nn . Ped iat. 1 98 : 35 8 , 19 62 .

22 . S H A H A N I, K . M . Iso latio n , characterization and sig -n i f icance o f ly soz y m e and lip ase in m ilk . Pro c . X V IIIIn te rnat. D airy C o ngr. lE : 61 , 19 70 .23 . H A Y A SA W A , H ., I. K IY O SA W A A N D T . N A G A SA W A .S o m e ob serv at ion s on h um an m ilk lip as e . Proc . X IXIn tern at. D airy C o ngr. IE : 5 59 , 19 74 .

24 . H E R N E L L , 0. H um an m ilk L ip ase s. I II. Ph y s io lo g ic alim p l ication s o f the b ile -salt s tim u lated l ipase . E u ro -pean J. C lin . Inv est . 5 : 2 67 , 197 5 .

25 . F R E D R IK Z O N , B ., A N D T . O L IV E C R O N A . D ecrease oflipas e and esteras e ac tiv itie s in in tes tinal co n te n ts o fn ew born in f an ts du rin g test m eals. Pe d iat. R es. 1 2 :6 31 , 19 78 .

26 . G Y#{246}RG Y, P. B ioc he m ic al asp ects . A m . J. C l in . N u tr.2 4 : 9 7 0 1 97 1

27 . T A R A S S U K , N . P., T . A . N IC K E R SO N A N D M . Y G UC H I. L ipase action in hum an m ilk . N ature 2 01: 29 8 ,1964 .

28 . B A B A B , H ., A N D W . Z . HA SSID. S o lu b le u rid ine d i-ph osp hate D -g alacto se: D -g luc ose a-4 -D -galactosy ltransf eras e f rom bo v in e m ilk . J. B io l. C h em . 24 1:2 6 7 2 1 9 6 6

29 . B A UM , J. D . N u tritio nal v alu e o f hum an m ilk . O b -ste t. G y n eco l. 3 7 : 1 26 , 197 1 .

30 . J E A N L O Z , R . W ., N . SH A R O N A N D H . M . F L O W E R S.T he ch em ical struc ture o f a d is acc haride iso late dfrom M icr oco ccu s l ysod ei kti cus ce ll w all. B ioch em .B iop hy s . R es. C o m m un . 1 3: 2 0 , 1 963 .


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rol and significance of enzymes in human milk

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