computing chapter 4 - ajums.ac.ir• detects any reducing sugar glucose oxidase • can be...
TRANSCRIPT
Chapter 4
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Introduction to Nutrition and Metabolism, 3rd edition
David A Bender Taylor & Francis Ltd, London 2002
Chapter 4: Digestion and Absorption
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The gastro-intestinal tract - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
oesophagus
ileum
rectum
duodenum
pancreas
caecum
appendix
gall bladder
liver
The gastro-intestinal tract - 2
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
salivary amylase
lingual lipase
gastric acid
pepsin
gastric lipase
alcohol absorption
bacterial fermentation
absorption of water
pancreatic amylase
lipase, phospholipase
trypsin, chymotrypsin, elastin
dipeptidases
disaccharidases
absorption of:
monosaccharides
amino acids
fatty acids, glycerol, fats
water
The intestinal mucosa - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
muscle
villi
The intestinal mucosa - 2
computing
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muscle
villi
Intestinal villi
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
muscle
villi
arterial blood supply venous drainage lymphatic drainage
lacteal
cell proliferation in crypt
cells shed at tip of villus
absorptive
enterocyte
mucus secreting
goblet cell
The intestinal mucosa - 3
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
muscle
villi
mucus secreting
goblet cell
Carbohydrates
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Carbohydrates
No requirement since can be made in the body
average diets provide 45% energy from carbohydrate
ideally this should be increased to 55%
composed of carbon, hydrogen and oxygen only
in the ratio C6H12O6
Nutritional classification of carbohydrates
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Nutritional classification of carbohydrates
sugars
monosaccharides
disaccharides
polysaccharides oligosaccharides sugar
alcohols
non-starch
polysaccharides
dextrins
trisaccharides
tetrasaccharides
intrinsic
sugars
extrinsic sugars
in free solution
lactose
in milk
non-milk
extrinsic
starch
Nutritionally important monosaccharides - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Nutritionally important monosaccharides
O
OH
OH
CH2OH
OH
H
H
H
HC O
C
CH
OH
C
HO
C
OH
CH2OH
OH
glucose
1
2
3
4
5
6
OH
galactose
H O
OH
OH
OH
O
CH2OH
H
H
HC O
C
CH
OH
CH
HO
C
CH2OH
OH
HO
fructose
HOCH2 O CH2OH
OH
O
OH
H
H
CH2OH
C
CH
O
C
HO
C
OH
CH2OH
OH
H
1
2
3
5
6
4
Nutritionally important monosaccharides - 2
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Nutritionally important monosaccharides
H
H
H
HC O
C
CH
OH
C
HO
C
OH
CH2OH
OH
O
OH
OH
CH2OH
OH
glucose
1
2
3
4
5
6
OHribose deoxyribose
HC O
C
C
OH
C
OH
CH2OH
OH
H
H
H
O OH
OHOH
HOCH2
HC O
CH
C
C
OH
CH2OH
OH
H
H
H
O OH
OH
HOCH2
Nutritionally important disaccharides - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Nutritionally important disaccharides
maltose (glucosyl-glucose)lactose (galactosyl-glucose)
sucrose (glucosyl-fructose)
O
OH
OH
O
CH2OH
H
HOCH2 O CH2OH
OH
O
OHO
O
OH
OH
OH
CH2OH
O
OH
OH
O
CH2OH
H
O
O
OH
OH
OH
CH2OHCH2OH
O
OH
OH
O
O
H
O
OH
OH
OH
CH2OH
CH2OH
O
OH
OH
O
OH
trehalose (glucosyl-glucoside)
H
Nutritionally important disaccharides - 2
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Nutritionally important disaccharides
isomaltosemaltose (glucosyl-glucose)
O
OH
OH
OH
CH2OHCH2OH
O
OH
OH
O
O H
H
CH2OH
O
OH
OH
O
O
CH2
O OH
OH
OH
O
H
Measurement of plasma or urine glucose
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Measurement of plasma or urine glucose
HC O
C
CH
C
C
CH2OH
OH
OH
OH
HO
H
H
H
COOH
C
CH
C
C
CH2OH
OH
OH
OH
HO
H
H
H
glucose gluconate
alkaline copper reagent
Cu++
Cu2O
(red-brown precipitate)
O2
H2O2
ABTS (colourless)
oxidised ABTS (blue)
H2O
glucose oxidase
peroxidase
Alkaline copper reagent
• only semiquantitative
• detects any reducing sugar
Glucose oxidase
• can be quantitative
• specific for glucose
• false negative with vitamin C
Branched structure of starch and glycogen
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
The branched structure of starch and glycogen
16 links: branch points inamylopectin and glycogen O
OH
OH
CH2OH
O
OH
OH
CH2OH
O O
O
OH
OH
CH2OH
O
OH
OH
CH2
O O O
O
O
O
OH
OH
CH2OH
O
O
OH
OH
CH2OH
Hydrolysis of starch by amylase
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Hydrolysis of starch by amylase
in saliva and pancreatic juice results in formation of dextrins,
then: glucose
maltose
isomaltose
16 links: branch points inamylopectin and glycogen O
OH
OH
CH2OH
O
OH
OH
CH2OH
O O
O
OH
OH
CH2OH
O
OH
OH
CH2
O O O
O
O
O
OH
OH
CH2OH
O
O
OH
OH
CH2OH
Major types of non-starch polysaccharides
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
cellulose - glucose polymer linked 14
O
OH
OH
CH2OH
O
O
OH
OH
CH2OH
O
OH
OH
CH2OH
O
OH
OH
CH2OH
O O O O
chitin - N-acetylglucosamine polymer linked 14
O
OH
CH2OH
O
O
OH
CH2OH
O
OH
CH2OH
O
OH
CH2OH
O O O O
HN C CH3
O
HN C CH3
O
HN C CH3
O
HN C CH3
O
pectin - galacturonic acid polymer linked 14, partially methylated; some glactose and/or arabinose branches
O
OH
OH
COOH
O
OH
OH
COOH
O
OH
OH
CO CH3
O
OH
OH
COOH
O O O OO
O CH2
OH
OH
O
HOCH2
O CH2
OH
OH
HOCH2
O CH2
OH
OH
HOCH2
O CH2
OH
OH
HOCH2
O
O
O
O
inulin - fructose polymer linked 21
The major types of non-starch polysaccharide
Glycaemic and non-glycaemic
carbohydrates - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Dietary starches can be classified as:
rapidly digested (hence high glycaemic index)
slowly digested (lower glycaemic index)
not all digested in small intestine
amylose is hydrolysed more slowly than amylopectin
resistant starch (low glycaemic index)
only hydrolysed to a limited extent in small intestine
starch may be resistant because:
it is crystalline and resistant to amylases
it is enclosed in plant cell walls that are not digested
some resistant starch is fermented by bacteria in the large intestine
Glycaemic and non-glycaemic carbohydrates
Glycaemic index
The extent to which a test dose of a carbohydrate increases blood glucose
compared with an equivalent amount of glucose
Glycaemic and non-glycaemic
carbohydrates - 2
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
sugars
monosaccharides
disaccharides
polysaccharides oligosaccharides sugar
alcohols
non-starch
polysaccharides
dextrins
trisaccharides
tetrasaccharides
intrinsic
sugars
extrinsic sugars
in free solution
lactose
in milk
non-milk
extrinsic
starch
Glycaemic and non-glycaemic carbohydrates
Disaccharidases and monosaccharide
absorption
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
inside mucosal cell mucosal cell membrane intestinal lumen
Na+
Na+
glucosegalactose
glucosegalactose
glucose transporter
maltose
2 x glucose
maltase
glucose + galactose
lactose
lactase
trehalose
2 x glucose
trehalase
sucrase fructose + glucose
sucrose
Na+ pump & Na+/K+ ATPase Na+ Na+
Monosaccharide absorption
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
inside mucosal cell mucosal cell membrane intestinal lumen
Passive diffusion
(carrier mediated)
fructose fructose
monosaccharides monosaccharides
sugar alcohols sugar alcohols
The importance of dietary fat
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
There is no absolute requirement for fat,
apart from small amounts of two polyunsaturated fatty acids
Fat provides 39 kJ /gram (cf protein 17 and carbohydrate 16 kJ /g)
at relatively high levels of intake it is easy to overeat
at very low levels of intake it is difficult to meet energy needs
the requirement is probably 10-15% of energy intake
Fat lubricates food in the mouth,
making chewing and swallowing easier
Much of the flavour in foods (especially meat) is in the fat
Vitamins A, D, E and K are present in dietary fat
and require fat for absorption
The importance of dietary fat
Triacylglycerols
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
H2C
CH
C
O
O
O
C
C
C
(CH2)n
O
(CH2)n
(CH2)n
O
O CH3
CH3
CH3H2
Triacylglycerols
3 x fatty acids esterified to glycerol
CH
CH2
CH2
O
O
O
O
O
O
Saturated and unsaturated fatty acids
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
polyunsaturated fatty acid (linoleic acid, C18:2 6)
mono-unsaturated fatty acid (oleic acid, C18:1 9)
saturated fatty acid (stearic acid, C18:0)
O
OH
O
OH
O
OH
Saturated and unsaturated fatty acids
Methylene interrupted double bonds
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Saturated and unsaturated fatty acids
Methylene interrupted double bonds
CH2
CH
CH
CH2
CH
CH
CH2
as opposed to conjugated double bonds
Cis- and trans-double bonds
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
cis
trans
Most unsaturated fatty acids are in the cis-configuration
trans-fatty acids occur as a result of:
• rumen bacterial fermentation – hence in beef, lamb, dairy produce
• isomerization during catalytic hydrogenation of oils
Saturated and unsaturated fatty acids
cis- and trans-double bonds
Fatty acid nomenclature
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
OH
O
C18:2 6 (linoleic acid)
OH
O
C18:3 3 (-linolenic acid)
6
O
OH9
C18:1 9 (oleic acid)
Fatty acid nomenclature
Saturated fatty acids
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Saturated fatty acids
no of C double bonds first C=C shorthand
butyric 4 0 - C4:0
caproic 6 0 - C6:0
caprylic 8 0 - C8:0
capric 10 0 - C10:0
lauric 12 0 - C12:0
myristic 14 0 - C14:0
palmitic 16 0 - C16:0
stearic 18 0 - C18:0
arachidic 20 0 - C20:0
behenic 22 0 - C22:0
lignoceric 24 0 - C24:0
Mono-unsaturated fatty acids
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
no of C double bonds first C=C shorthand
palmitoleic 16 1 6 C16:1 6
oleic 18 1 9 C18:1 9
cetolic 22 1 11 C22:1 11
nervonic 24 1 9 C24:1 9
Mono-unsaturated fatty acids
Polyunsaturated fatty acids
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
no of C double bonds first C=C shorthand
linoleic 18 2 6 C18:2 6
-linolenic 18 3 3 C18:3 3
g-linolenic 18 3 6 C18:3 6
arachidonic 20 4 6 C20:4 6
eicosapentaenoic 20 5 3 C20:5 3
docosatetraenoic 22 4 6 C22:4 6
docosapentaenoic 22 5 3 C22:5 3
docosapentaenoic 22 5 6 C22:5 6
docosahexaenoic 22 6 3 C22:6 3
Polyunsaturated fatty acids
Phospholipids
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
OH
OHHO
HO OH
phosphatidylserine phosphatidylethanolamine phosphatidylcholine(lecithin)
phosphatidylinositol
CH2 CH
COO-
NH3+ CH2 CH2 NH3
+ CH2 CH2 N+
CH3
CH3
CH3
Major water-soluble groups in phospholipids
P O-O
O
O
R
O
O
CHO
CH2
CH2
O
Phospholipids
Phospholipids in cell membranes
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Phospholipids in cell membranes
outside
inside
cell surface protein
intracelluar
membrane protein
transmembrane
receptor protein
transmembrane protein
forming a transport pore
Cholesterol and steroid hormones
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
O
O
HO OH
O
O
HOCH2
cortisol
OH
O
testosterone
progesterone
OH
HO
oestradiol
HO HO HO
cholesterol -sitosterol cholestanol
Cholesterol and some steroid hormones
Triacylglycerol digestion - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
O
O
O
CH
CH2
CH2
O
O
O
triacylglycerol – insoluble in water
glycerolHO CH
CH2
CH2
OH
OH
O
OH
O
OH
O
OH
free fatty acids
Triacylglycerol digestion
Cholesterol and bile salt metabolism - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
cholesterol secretion 2g /daycholesterol
cholesterol synthesis
conjugates
primary bile salts
cholesterol
bile salt conjugates 30 g /day
bacterial deconjugation
cholate + chenodeoxycholate
bacterial metabolism
deoxycholate + lithocholate
dietary cholesterol
0.5 g/day
faecal steroids
+ bile salts
1 – 2 g /day
Cholesterol and bile salt metabolism
Cholesterol and bile salt metabolism - 2
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
glycochenodeoxycholic acidtaurochenodeoxycholic acid
glycocholic acidtaurocholic acid
conjugation with glycine or taurine
HO OH
OHCOOH
chenodeoxycholic acid cholic acid
cholesterol
HO OH
COOHHO
HO
COOH
HO
OHCOOH
deoxycholic acidlithocholic acid
intestinal bacterial deconjugation and metabolism
C
R
N
O
C
H
COO-
H
H
C
R
N
O
C
H
C
H
H
SO3-
H
H
glycine conjugates
taurine conjugates
Cholesterol and bile salt metabolism
Incidence of gallstones with obesity
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
0
1
2
3
4
5
6
7
8
rela
tiv
e r
isk
<24 24.5 25.5 26.5 28 29.5 32.5 37.5 42.5 >45
body mass index
The incidence of gallstones with obesity
Triacylglycerol digestion - 2
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
H2C
CH
C
O
O
O
C
C
C
(CH2)n
O
(CH2)n
(CH2)n
O
O CH3
CH3
CH3H2
H2O
triacylglycerol
diacylglycerol
lipase
H2C
CH
C
O
OH
O C
C(CH2)n
(CH2)n
O
O
CH3
CH3H2
CH3 (CH2)n COOH
free fatty acid
free fatty acidCH3 (CH2)n COOH
H2C
CH
C
O
OH
OH
C(CH2)n
O
CH3
H2
lipase
monoacylglycerol
H2O
H2C OH
CH
C OH
OH
H2
H2O
pancreatic esterasesand intracellular lipase
glycerol
CH3 (CH2)n COOH
free fatty acid
lipases:
hydrolyse ester bonds in triacylglycerol
• lingual lipase – secreted by tongue
• gastric lipase – secreted in stomach
• pancreatic lipase – secreted by pancreas
Formation of lipid micelles
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Due to the emulsifying action of:
free fatty acids
diacylglycerols
monoacylglycerols
phospholipids
bile salts
hydrophilic group
hy
dro
ph
ob
ic t
ail
hydrophobic core contains:
cholesterol
fat-soluble vitamins (A, D, E and K)
carotenes
other lipids
The formation of lipid micelles small enough to be absorbed
Re-esterification in the intestinal mucosa
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
CoASH
CH3 (CH2)n COOH
ATP
AMP + pyrophosphate
CH3 (CH2)n C SCoA
O
fatty acid
fatty acyl CoA
the reaction of acyl CoA synthase
NAD+NADH
glycerol 3-phosphate dehydrogenase
dihydroxy-acetonephosphate
H2C OH
C
C O P
O
H2
glycerol phosphate
H2C OH
CH
C O P
HO
H2
CoASH
fatty acyl CoA
monoacylglycerol phosphate
H2C O
CH
C O P
C (CH2)n
O
CH3
HO
H2
diacylglycerol phosphate
CoASH
fatty acyl CoA
H2C O
CH
C O P
C (CH2)n
O
CH3
OCO
O
(CH2)nCH3
H2
H3PO4
triacylglycerol
CoASH
fatty acyl CoA
H2C O
CH
C O C
C (CH2)n
O
CH3
O
(CH2)n
O
CH3
CO
O
(CH2)nCH3
H2
H2O
Re-esterification in the intestinal mucosa
Assembly of chylomicrons
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Re-esterified triacylglycerols are packaged with:
proteins
phospholipids
cholesterol and cholesterol esters
carotenes and fat-soluble vitamins
to form chylomicrons
85 – 90% triacylglycerol
75 – 1200 nm diameter
Chylomicrons are absorbed into the lymphatic system
enter the bloodstream at the thoracic duct
Tissues take up fatty acids from triacylglycerol
by action of lipoprotein lipase at cell surface
Chylomicron remnants are cleared by the liver
Assembly of chylomicrons
Protein is 13 – 15% of body mass
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
water
64%
essential fat
3%storage fat
12%protein
15%
minerals
6%
water
54%essential fat
9%
storage fat
19%
protein
13%
minerals
5%
Protein is 13 – 15% of body mass
The amino acids
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
N COO-
glycine (Gly, G) alanine (Ala, A) proline (Pro, P)
small neutral amino acids
large neutral amino acids
*methionine (Met, M)
*leucine (Leu, L) *valine (Val, V)
*isoleucine (Ile, I)
branched-chain amino acids
aromatic amino acids
*phenylalanine (Phe, F)
tyrosine (Tyr, Y)
hydrophobic amino acids
basic amino acids
*lysine (Lys, K)
arginine (Arg, R)
*histidine (His, H)
amino acid amides
asparagine (Asn, N) glutamine (Gln, Q)
acidic amino acids
aspartate (Asp, D) glutamate (Glu, E)
neutral hydrophilic amino acids
hydrophilic amino acids
serine (Ser, S) *threonine (Thr, T) cysteine (Cys, C)
*tryptophan (Trp, W)
H
HCH
NH3+
COO-
CH
NH3+
COO-
CH2CHH3C
CH3
CH
NH3+
COO-
H3C
CH
NH3+
COO-
CH2CH2CH2CH2+H3N
CH
NH3+
COO-
CHH3C
CH3
CH
NH3+
COO-
CHCH2
CH3
H3CCH
NH3+
COO-
CH2CH2SH3C
CH
NH3+
COO-
CH2
CH
NH3+
COO-
CH2HO
N
CH
NH3+
COO-
CH2
CH
NH3+
COO-
CH2HO CH
NH3+
COO-
CH2HSCH
NH3+
COO-
CHH3C
OH
CH
NH3+
COO-
CH2CH2-OOCCH
NH3+
COO-
CH2-OOC
CH
NH3+
COO-
CH2CH2N
O
CH
NH3+
COO-
CH2CH2CH2N
O
CH
NH3+
COO-
CH2
N N
CH
NH3+
COO-
CH2CH2CH2NHCHN
NH2
HH
The amino acids (* indicates dietary essential amino acids)
Formation of the peptide bond
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
H2O
C CN N C C
H
COOHH2N
H O R2
R1 H H O
C CN
H
H2N OH
H O
R1
N C C COOH
H R2
H H O
+
H2Ocondensation
hydrolysis
Formation of the peptide bond
Hydrogen bonds between peptide bonds in a peptide chain
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
C CN N C C
H
COOHH2N
H O R2
R1 H H O
CC NNCC
H
COOH NH2
HOR2
RHHO
CC NNCC
H
COOH NH2
HOR2
RHHO
Hydrogen bonds between peptide bonds in a peptide chain
Side-chain links between peptide chains
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
CH2
CH2
NH2
CH2
CH2
CHHN CO
CHHN
CH2
CO
CH2
COOH
H2O
CH2
CH2
NH
CH2
CH2
CHHN CO
C
CH2
O
CH2
CH COHN
glutamate
lysine
condensation
CHHN
CH2
CO
SH
CHHN
CH2
CO
SH
cysteine
cysteine
XXH2
oxidation
CHHN
CH2
CO
S
S
CH2
CHHN CO
cystine
Side-chain links between peptide chains
Native proteins are relatively resistant to enzymic hydrolysis
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Native proteins are relatively resistant to enzymic hydrolysis
the first step in digestion is disruption of H-bonds:
heat
gastric acid
so as to leave a straight peptide chain
that is accessible to digestive enzymes
C CN N C C
H
COOHH2N
H O R2
R1 H H O
CC NNCC
H
COOH NH2
HOR2
RHHO
CC NNCC
H
COOH NH2
HOR2
RHHO
C CN N C C
H
COOHH2N
H O R2
R1 H H O
CC NNCC
H
COOH NH2
HOR2
RHHO
CC NNCC
H
COOH NH2
HOR2
RHHO
Hydrolysis of the peptide bond
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
H2O
C CN
H
R1
O
N C
H H
R2
C
O
H
COOHH2N
C CN
H
R1
OH
H2N OH N C
H H
R2
C
O
COOH
H
In vitro 10 – 12 hours in 12 mol /L HCl at 105ºC, random hydrolysis of peptide bonds
In vivo 1 – 2 hours at 37ºC, specific bonds hydrolysed
Hydrolysis of the peptide bond
The serine proteases, chymotrypsin, trypsin and elastase - 1
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Bonds hydrolysed:
trypsin
esters of basic aa
chymotrypsin
esters of aromatic aa
elastase
esters of small neutral aa
The serine proteases, chymotrypsin, trypsin and elastase
The serine proteases, chymotrypsin, trypsin and elastase - 2
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
substrate sits in a groove
on the enzyme surface
bond to be cleaved
lies over catalytic site
The serine proteases, chymotrypsin, trypsin and elastase
Trypsin
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
-
Gly
Gly
Asp
-
+
peptide in groove on enzyme surface
trypsin
Bonds hydrolysed:
trypsin
esters of basic amino acids
chymotrypsin
esters of aromatic amino acids
elastase
esters of small neutral amino acids
The serine proteases, chymotrypsin, trypsin and elastase
Chymotrypsin
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Gly
Gly
Ser
peptide in groove on enzyme surface
chymotrypsin
Bonds hydrolysed:
trypsin
esters of basic amino acids
chymotrypsin
esters of aromatic amino acids
elastase
esters of small neutral amino acids
The serine proteases, chymotrypsin, trypsin and elastase
Elastase
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Val
Thr
Gly
peptide in groove on enzyme surface
elastase
Bonds hydrolysed:
trypsin
esters of basic amino acids
chymotrypsin
esters of aromatic amino acids
elastase
esters of small neutral amino acids
The serine proteases, chymotrypsin, trypsin and elastase
Endopeptidases
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Endopeptidases
hydrolyse specific peptide bonds within the protein chain
pepsin gastric juice amides of Phe, Tyr, Trp, Leu, Met
enteropeptidase succus entericus trypsinogen trypsin
trypsin pancreatic juice Arg, Lys esters
chymotrypsin Phe, Tyr, Trp esters
elastase neutral aliphatic esters
pancreatic juice
pancreatic juice
Exopeptidases
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Exopeptidases
hydrolyse specific peptide bonds of terminal amino acids
dipeptidases brush border various dipeptides
carboxypeptidase A pancreatic juice C-terminal large neutral aa
carboxypeptidase B pancreatic juice C-terminal Lys, Arg
aminopeptidases various N-terminal aa succus entericus
Peptidases are secreted as inactive
zymogens
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Peptidases
secreted as inactive zymogens and activated after secretion
pepsinogen pepsin gastric acid, then pepsin
trypsinogen trypsin enteropeptidase
chymotrypsinogen chymotrypsin trypsin
pro-elastase elastase trypsin
procarboxypeptidases carboxypeptidase trypsin
pro-aminopeptidases aminopeptidases trypsin
substrate-binding cleft
masked by terminal region of protein
in zymogen
End
computing
Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd
Introduction to Nutrition and Metabolism, 3rd edition
David A Bender Taylor & Francis Ltd, London 2002
Chapter 4: Digestion and Absorption
End of presentation The peptide sequence simulation on the CD accompanies this Chapter