Biochemical Engineering Journal 30 (2006) 82–87

Purification and characterization of a bifunctional enzyme withchitosanase and cellulase activity from commercial cellulase

Jing Liu a,b,1, Wenshui Xia a,c,∗a Key Laboratory of Food Science and Safety, Ministry of Education, Southern Yangtze University, Wuxi 214036, Jiangsu, PR China

b Jiangsu Animal Husbandry and Veterinary College, Taizhou 225300, Jiangsu, PR Chinac Wuhan Polytechnic University, Wuhan 430023, Hubei, China

Received 7 October 2005; received in revised form 6 February 2006; accepted 6 February 2006

Abstract

A bifunctional enzyme with chitosanase and carboxymethyl cellulase (CMCase) activity was purified from commercial cellulase, which wasproduced by trichoderma viride, through sequential steps of DEAE-Sepharose CL-6B ion-exchange chromatography, Phenyl Sepharose CL-4Bhydrophobic interaction chromatography and Sephadxe G-75 gel filtration. The purified hydrolase was homogeneous as examined by sodiumdodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular mass was 66 kDa. The hydrolase exhibited chitosanase activityfpFiig©

K

1

ttiifiinc

YT

X

UT

1d

or chitosan hydrolysis and cellulase activity for carboxymethyl cellulose (CMC) hydrolysis. For chitosan hydrolysis, the enzyme had an optimumH of 5.2, temperature of 60 ◦C and exhibited typical Michaelis-Menten kinetics with Km value and Vmax of 10 mg/ml and 0.164 U/ml, respectively.or CMC hydrolysis, the pH and temperature optima enzyme were 4.0 and 50 ◦C. Heavy metal ions such as Hg2+, Ag+ significantly or completely

nhibited the enzyme activity. Identification of glucosamine (GlcN) and N-acetyl-glucosamine (GlcNAc) oligomers as depolymerized productsndicated that the enzyme cleaved both GlcN-GlcN and GlcNAc-GlcN linkages. The chitosan hydrolysates were oligomers with one to fourlucosamine residues and some oligomers with longer chain length.

2006 Elsevier B.V. All rights reserved.

eywords: Cellulase; Chitosanase; Bifunctional; Properties; trichoderma viride

. Introduction

Chitosanolytic enzymes are increasingly gaining impor-ance as low molecular weight chitosans (LMWC) and chi-ooligomers, the products of depolymerization, which shownnumerable applications in various fields, such as the biomed-cal, pharmaceutical, agricultural, biotechnological and foodelds [1–3]. But the utility of chitosanase in hydrolysis is lim-

ted because of its cost and unavailability in bulk quantities. Aumber of non-specific enzyme such as lysozyme, papin, lipase,ellulose, pectin lyase [4–9] have been used in free or immobi-

∗ Corresponding author at: School of Food science and Technology, Southernangtze University, Huihe Road 170, P.O. Box 60, Wuxi 214036, PR China.el.: +86 510 5869455; fax: +86 510 5812812.

E-mail addresses: Norman qjz@yahoo.com.cn (J. Liu),iaws@pub.wx.jsinfo.net (W. Xia).1 Present address: School of Food science and Technology, Southern Yangtzeniversity, Huihe Road 170, P.O. Box 60, Wuxi 214036, PR China.el.: +86 510 5869455; fax: +86 510 5812812/523 6663808.

lized forms for hydrolysis of chitosan for preparation of chitosanhydrolysate with different molecular masses.

Cellulase constitutes a complex enzymatic system respon-sible for the degradation of cellulose substances and hasa non-specific hydrolytic action in hydrolysis chitosan hasbeen reported. The �-1,4 glucanase capable of degrading car-boxymethyl cellulose and fully deacetylated chitosan was firstpurified from Myxobacter A-L1 [10]. By using this informationthe chitosanase-cellulose activity was further synthesized duringthe growth cycle of Myxobacter sp. A-L1 and purified by cation-exchange and molecular-exclusion chromatography [11]. Alsothere were some other cellulase with chitosanase activity foundfrom Streptomyces griseus MUT6037 [12] and Bacillus mega-terium P1 [13] over the last decade. In some case chitosanaseand CMCase activites were comparable, in others they were not.However, the relationship of the enzyme between structure andbifunction was still in doubt. To further identify the action modeof the bifunctional enzyme, the objective of the present study wasto purify and characterize the chitosanolytic enzyme from com-mercial cellulase and to determine its biochemical properties.

369-703X/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.bej.2006.02.005

J. Liu, W. Xia / Biochemical Engineering Journal 30 (2006) 82–87 83

2. Materials and methods

2.1. Crude enzyme and chemical

Crude enzyme preparation from Trichoderma viride contain-ing CMCase activity of 15 U/mg was purchased from SinopharmMedicine Holding Co. Ltd. Chitosan dimer, chitosan trimer, chi-tosan tetramer, chitosan pentamer, and chitosan hexamer wereobtained from Seikagaku Company. Chitosan was purchasedfrom Yuhuan Co. Zhejiang, China. DEAE-Sepharose CL-6B,Pheny Sepharose CL-4B, Sephadex G-75 and low molecu-lar weight protein standard were obtained from Pharmacia.p-Nitrophenyl (PNP) glucosides was purchased from Sigma.Buffer salts and other reagents were of analytical grade andfrom commercial sources.

2.2. Enzyme purification

2.2.1. DEAE sepharose CL-6B ion exchangechromatography

The enzyme solution was applied to a DEAE Sepharose CL-6B column (2.6 cm × 45 cm) that had been equilibrated with20 mM phosphate buffer, pH 6.8. After the column was washedthoroughly with the buffer, a linear gradient elution was madewith the buffer containing NaCl added from 0.0 to 2.0 M. Frac-tions of 5 ml each were collected, and those active fractionswda

2c

f(pwwt2ad

2

StuFws

2

2

i

buffer from 3.0 to 8.0 using chitosan or CMC as the substrateand incubated in 60 or 50 ◦C for 30 min. For pH stability, theenzyme was treated at various pHs at 30 ◦C for 24 h. The pH ofenzyme solution was then adjusted to 5.2 or 4.0 and the remain-ing activities were measured.

2.3.2. Effect of temperature on enzyme activity andstability

The optimum temperature of the chitosanolytic and cellu-lolytic activity of the purified enzyme was assayed at pH 5.2 or4.0 from 30 to 80 ◦C for 30 min. The enzyme was treated at dif-ferent temperatures (30–80 ◦C) for 2 h at pH 5.2 or 4.0 withoutthe addition of substrate and was withdrawn at precise intervalsto investigate thermal stability. The remaining activities weremeasured.

2.3.3. Michaelis constant (Km) and maximal velocity(Vmax) determination

Michaelis constant (Km) and maximal velocity (Vmax) ofthe purified enzyme for chitosan and CMC were determinedas follows: use 1.5 ml chitosan solution in 20 mM acetatedbuffer, pH 5.2 or 1.5 ml CMC in 20 mM acetated buffer,pH 4.0 in concentration from 1.0 to 5.0 mg/ml as substrate,add 0.5 ml diluted enzyme solution and incubated at 60 or50 ◦C for 10 min. The reducing sugar produced was mea-sured colorimetrically with Ferri-ferrocyanide reagent [14].Tp[

2

smrt

2

tSpbiSaRBrra

2

Lt2

ith bifunction were pooled, concentrated by dialysis, and thenissolved with phosphate buffer containing 1.0 M saturation ofmmonium sulfate.

.2.2. Phenyl Sepharose CL-4B hydrophobic interactionhromatography

The enzyme solution saturated with 1.0 M ammonium sul-ate was loaded onto a Phenyl Sepharose CL-4B column1.6 cm × 25 cm) previously equilibrated with the 20 mM phos-hate buffer (pH 6.8) containing 1.0 M ammonium sulfate andashed with the same buffer. A linear gradient was doneith the buffer containing ammonium sulfate added from 1.0

o 0.0 M saturation, then washed with phosphate buffer and0% ethanol (v/v). Fractions of 5 ml each were collected,nd the active fractions were pooled and concentrated byialysis.

.2.3. Sephadex G-75 gel filtrationThe enzyme solution was put through gel filtration with a

ephadex G-75 column (1.0 cm × 100 cm) pre-equilibrated withhe 20 mM phosphate buffer containing 50 mM NaCl. The col-mn was eluted with the same buffer at a flow rate of 12 ml/h.ractions of 5 ml each were collected, and the active fractionsere pooled, dialyzed, and concentrated by lyophilization and

tored at −18 ◦C.

.3. Characterization of purified enzyme

.3.1. Effect of pH on enzyme activity and stabilityThe optimum pH of the chitosanolytic and cellulolytic activ-

ties for the purified enzyme was assayed in a 0.2 M universal

he Vmax and Km were calculated from double-reciprocallots according to the method of Lineweaver and Burk15].

.3.4. Effect of metal ions and some other reagentsThe purified enzyme was incubated with ion and EDTA

olution at 30 ◦C for 30 min. The hydrolysis activity was theneasured. The relative activity was expressed as the percentage

atio of the specific activity of the enzyme with metals or saltso that of without metals or salts.

.3.5. Determination of enzyme molecular weightThe molecular weight of the enzyme was determined by

he Sephadex G-75 gel filtration with standard proteins andDS-PAGE according to the method of Laemmli [16]. Phos-horylase b (97.4 kDa), bovine serum albumin (66.2 kDa), oval-umin (45 kDa), carbonic anhydrase (31 kDa), soybean trypsinnhibitor (21.5 kDa) and lysozyme (14.4 kDa) were used asDS-PAGE standard makers. The protein bands on the gelfter electrophoresis was visualized by silver staining. TheP-HPLC of purified enzyme was carried out using a ZOR-AX C8 reverse phase column (25 cm × 4.6 mm) at a flow

ate of 1.0 ml/min using a linear gradient of (a) 0.1% trifluo-oacetic acid (TFA), (b) acetonitrile:water (70:30) and detectedt 280 nm.

.3.6. Determination of proteinThe protein concentration was measured using the method of

owry et al. [17] with bovine serum albumin as a standard. Forhe purified enzyme, protein was measured by the absorbance at80 nm.

84 J. Liu, W. Xia / Biochemical Engineering Journal 30 (2006) 82–87

2.4. Analytical methods

2.4.1. Determination of chitosanase, CMCase, glycosidaseactivities

Chitosanase activity of the enzyme was measured by incu-bating 0.5 ml of the purified enzyme with 1.5 ml of 0.5% (w/v)chitosan (deacetylation degree (DD) 90%, molecular weight560 kDa) in 20 mM acetate buffer, pH 5.2 at 60 ◦C for 30 min.The reaction was stopped by heating it at 100 ◦C for 8 min.Reducing sugar produced by this reaction was measured accord-ing to the 3,5-dinitrosalicylic (DNS) reagent method [18]. d-glucosamine was used as a standard. One unit of enzyme wasdefined as the amount of enzyme that released 1 �mol of reduc-ing sugar per minute.

CMCase activity of the enzyme toward CMC (degree of sub-stitution of 0.66–0.95) was determined by replacing chitosan inthe 20 mM acetate buffer, pH 4.2 at 50 ◦C for 30 min. All theactivity measurements were performed three times.

These two methods above were used to assay enzyme activi-ties during enzyme purification, as well as in the study of pH andtemperature optima, substrate specificity and enzyme kinetics onpurified enzyme.

Glycosidase activities were assayed by measuring the amountof p-nitrophenyl released from 1 mM substrate of the respec-tive p-nitrophenyl glycosides by incubation in 0.2 ml of 50 mMacetate buffer, pH 4.6 for 4 h at 37 ◦C. The reaction was termi-nm

2

HNTsat

2

2ratps(0

3

3

3

ro

Fig. 1. Ion-exchange chromatography of cellulase on DEAE-Sepharose CL-6Bcolumn. The column was equilibrated with 20 mM acetate buffer, pH 6.8. Fivemilliliters of cellulase was applied. The column was washed with 100 ml of theequilibrium buffer and eluted with 400 ml of a linear gradient of 0–2.0 M phos-phate buffer, pH 6.8 at a flow rate of 60 ml/h. Fractions of 5 ml were collected.

hydrophobic interaction chromatography on a Phenyl SepharoseCL-4B column and gel filtration on a Sephadex G-75 column.As shown in Fig. 1, a protein peak containing chitosanase andCMCase activities and two other protein peaks just with CMCaseactivity were eluted from the ion-exchange chromatograph ofSepharose CL-6B. Fraction with bifunction was collected, andothers were removed using this procedure. Hydrophilic chro-matography of the ion exchange purified bifunctional fractionon Phenyl Sepharose CL-4B resulted in one protein peak (peak2) with bifunction and two protein peaks just with chitosanase(peak 1) or cellulase activity (peak 3) as shown in Fig. 2.Enzymes obtained from Phenyl Sepharose CL-4B were furtherpurified on a Sephadex-G-75 column and a major protein peakwas obtained as shown in Fig. 3. The purification results are sum-marized in Table 1. Through these steps, the enzyme was purified3.16-fold with a recovery of 10.47%. The recovery of the enzymeactivity was rather low due to the removal of some minor activ-

FTTaasa

ated by the addition of 0.2 M Na2CO3 (0.8 ml), and they wereonitored at 420 nm.

.4.2. Chitosan deacetylation degree (DD) determinationThe chitosan (0.3 g) was dissolved in a known excess of 0.1 M

Cl acid (20 ml). From the titration of this solution with a 0.1 MaOH solution, a curve with two inflexion points was obtained.he difference between the volumes at these two points corre-ponded to the acid consumed for esterification of amine groupsnd allowed the determinationed of DD of the chitosan. Theitration was performed with a DELTA-320-S pH meter.

.4.3. Thin layer chromatography (TLC) of hydrolysatesThe enzyme (0.5 ml) was incubated with 1% chitosan in

0 mM acetate buffer, pH 5.2 at 60 ◦C. After an appropriateeaction time, a portion of the reaction mixture was withdrawnnd boiled for 8 min to stop the enzymatic reaction. To analyzehe chitosan oligosaccharide with TLC, the supernatants pre-ared under the conditions described above were spotted on ailica gel plate and developed with n-propanol:water:ammonia70:30:1). The sugar on the TLC plate was stained by spraying.1% ninhydrin dissolved with 99% ethanol.

. Results and discussion

.1. Results

.1.1. Enzyme purificationA hydrolase with both chitosanase and cellulase activity was

ecovered from commercial cellulase by using a combinationf Sepharose CL-6B column anion exchange chromatography,

ig. 2. Hydrophilic chromatography of cellulase on Phenyl Sepharose CL-4B.he column was equilibrated with 1.0 M ammonium sulfate buffer, pH 6.8.wo milliliters of DEAE-Sepharose CL-2B purified bifunctional enzyme waspplied. The column was washed with 50 ml 1.0 M ammonium sulfate buffernd eluted with 200 ml a linear gradient buffer with 0–1.0 M ammonium sulfateaturation, 50 ml 20 mM, pH 6.8 phosphate buffer and 50 ml of 20% ethanol atflow rate of 1 ml/min. Fractions of 5 ml were collected.

J. Liu, W. Xia / Biochemical Engineering Journal 30 (2006) 82–87 85

Fig. 3. Gel filtration of cellulase on Sephadex G-75 column. The column wasequilibrated with 20 mM phosphate buffer containing 0.1 M NaCl, pH 6.8. Twomilliliters of Phenyl Sepharose CL-4B purified bifunctional enzyme was applied.The column was eluted with the equilibrium buffer at a flow rate 12 ml/h. Fractionof 2 ml were collected.

ity peaks during chromatography or some of the activity lossesoccurred during dialysis and lyophilization steps. Even thoughthe recovery fold is the lowest when using gel filtration, it is anecessary method to change the enzyme buffer for further deter-mination enzyme activity. The purification fold of CMCase isnot in agreement with that of chitosanase, maybe owing to threefactors: the degrading CMC is a synergistic action of coenzymebut most of the cellulase active portion was removed duringthe purification procedure; the CMCase activity was determinedby 3,5-dinitrosalicylic acid method which only measuring thereducing sugar; the bifunctional enzyme may has two differentactive centers, although one enzyme possesses both activities.

3.1.2. Molecular mass and the purity of the enzymeThe molecular mass of the enzyme was 66.0 kDa as estimated

by SDS-PAGE. This value was close to the value of 64.0 kDaestimated by gel filtration on Sephadex G-75. SDS-PAGE of thepurified enzyme (Fig. 4) showed the presence of a single protein.

3.1.3. Effect of pH on the enzyme activity and stabilityThe purified enzyme had an optimal pH of 5.2 for chitosan

and an optimal pH of 4.2 for CMC hydrolysis, respectively.

Fig. 4. SDS-PAGE of purified enzyme. Lane S indicate standard proteins: Phos-phorylase b (97.4 kDa), bovine serum albumin (66.2 kDa), ovalbumin (45 kDa),carbonic anhydrase (31 kda), soybean trypsin inhibitor (21.5 kda), lysozyme(14.4 kDa). Lanes 1 and 2 indicate purified enzyme with proteins of 164.4 and364 �g/ml, respectively.

When the enzyme was kept at 30 ◦C in a universal buffer, pH3.0–8.0 for 24 h, the enzyme stability was at pH 3–7 for bothactivations.

3.1.4. Effect of temperature on the enzyme activity andthemostability

The purified enzyme had an optimum temperature of 60 ◦Cfor chitosan hydrolysis and 50 ◦C for CMC hydrolysis. Theenzyme was stable in the range of 30–70 ◦C when it was incu-bated at 30–80 ◦C for 30 min to 2 h although enzyme activitywas nearly lost after 15 min at 80 ◦C.

3.1.5. Effect of metal ions, EDTA on enzyme activityAs shown in Table 2, the activity for chitosan hydrolysis was

not affected by K+, Na+, Ba2+ and EDTA. Co2+, and Mn2+ ionssignificantly increased the activity while Hg2+, Ag2+, Pb2+, andCu2+ decreased it. This result was similar to those for otherchitosanolytic enzymes and suggested the metal ions were notessential for the catalytic action of the enzyme.

Table 1Purification of chitosanase from cellulose

S ) Specific activity (units/mg) Recovery (%) Purification (fold)

CMCase Chitosanase CMCase Chitosanase

C 0D 0

P00

P00

equential step Total activity (units) Total protein (mg

CMCase Chitosanase

rude enzyme 12.5 6.53 51.2EAE-Sepharose CL-6B 3.58 3.88 22.5

eak 1Phenyl Sepharose CL-4B 0.98 2.91 5.81Sephacryl S-200 0.00 3.56 5.62

eak 2Phenyl Sepharose CL-4B 1.44 2.27 5.46Sephacryl S-200 1.38 2.15 5.34

.244 0.127 100.0 1.00 1.00

.159 0.172 44.1 1.35

.168 0.502 11.4 3.95

.00 0.635 11.0 0.00 5.00

.264 0.416 10.7 1.08 3.27

.258 0.402 10.5 1.05 3.16

86 J. Liu, W. Xia / Biochemical Engineering Journal 30 (2006) 82–87

Fig. 5. Thin layer chromatography of chitosan hydrolysates. Lanes A1–A8 denoted chitosan hydrolysates, which were hydrolyzed by the crude enzyme at 60 ◦C for0.5, 1,2, 4, 6, 8, 10, and 12 h, respectively. Lanes B1–B8 denoted hydrolysates of DD 73, 75,78, 83, 85, 87, 90 chitosan by crude enzyme at 60 ◦C for 6 h. Lane Sdenoted standard chitooligosaccharides: glucosamine, chitobiose, chitotriose, chitotetraose, chitopentaose, and chitohexose.

3.1.6. Michaelis constant and maximal velocityThe substrate concentration effect on the hydrolase rate

for chitosan and CMC was determined. The Michaelis con-stant (Km) and maximum velocity (Vmax) were calculated fromLineweaver–Burk plots. The enzyme had a Km of 0.10 mg/mland Vmax of 0.164 �mol glucosamine/min/ml for chitosanhydrolysis, and it had Km of 0.88 mg/ml and a Vmax of 3.50 �molof glucose/min/ml for CMC hydrolysis.

3.1.7. Effect of the deacetylation degree (DD) on theenzyme activity

As shown in Table 3 and Fig. 5 (B1–B8), chitosan polymerexhibiting different deacetylation degree were all susceptible tothe crude enzyme, and released the same chitooligosaccharidesproducts.

3.1.8. Chitosan hydrolysates and chitooligosaccharidehydrolysis

As shown in Fig. 5, the products of chitosan hydrolysis bycrude enzyme for 0.5–12 h were chitobiose, chitotriose, chitote-

Table 2Effect of metal ions, EDTA, DTT on the enzyme activity

Metal ion Content (mmol/l) Relative activity (%)

None – 100.0BSAAHPCMCMMMCZFED

traose, and some chitooligasaccharides with long chain length.The shorter oligomer of d-glucosamin increased as digestiontime increased (lanes A1–A8). Hydrolysis products generatedby the actions of the purified enzyme on chitooligosaccharidesare shown in Fig. 6. After reaction for 1 and 6 h, chitobiose,chitotriose, chitotetraose and chitopentaose were hydrolyzed bythe purified enzyme and released glucosamine and other shorterchitooligosaccharides.

Table 3Effect of the degree of chitosan deacetylation on the crude enzyme activity

Substrate (0.5%) Relative activity (%)

Chitosan (90% DD) 96Chitosan (85% DD) 90Chitosan (83% DD) 90Chitosan (75% DD) 100CMC 800

Fig. 6. Thin layer chromatography of chitooligosaccharide hydrolysates. Lanes1, 3, 5, 7, 9 denoted glucosamine, chitobiose, chitotriose, chitotetraose and chi-topentaose hydrolysis by the purified enzyme at 60 ◦C for 1 h. Lanes 2, 4, 6, 8,10denoted glucosamine, chitobiose, chitotriose, chitotetraose and chitopentaosehydrolysis by the purified enzyme at 60 ◦C for 6 h. Lane S denoted standardchitooligosaccharide: glucosamine, chitobiose, chitotriose, chitotetraose, chi-topentaose and chitohexose.

aCl2 2.50 100.0 ± 0.8nCl2 2.50 109.4 ± 0.6gCl 1.00 80.6 ± 2.3gCl 2.50 62.0 ± 2.2gCl2 1.00 20.7 ± 2.2b(CH3COO)2 1.00 24.5 ± 0.8oSO4 2.50 116.5 ± 1.3gSO4 2.50 119.7 ± 2.5uSO4 2.50 21.9 ± 1.6nSO4 0.50 110.8 ± 1.4nSO4 1.00 114.0 ± 1.6nSO4 3.00 118.6 ± 2.0a(CH3COO)2 5.00 106.7 ± 1.4n(CH3COO)2 5.00 85.6 ± 1.2e2(SO4)3 5.00 86.5 ± 1.2DTA 0.10 100.0 ± 1.3TT 0.10 100.0 ± 0.9

J. Liu, W. Xia / Biochemical Engineering Journal 30 (2006) 82–87 87

3.2. Discussion

Cellulase capable of hydrolyzing chitosan was searched for invarious commercially available enzyme preparations. One cel-luase specimen, T. viride, was found to exhibit high activityand was thus selected as a source for purification. This paperdescribed the purification and characterization of bifunctionalenzyme with both chitosanase and CMCase activity from T.viride. The molecular mass of the purified enzyme was 64 kDaby gel filtration, and 66 kDa, a similar value as estimated bySDS-PAGE. This suggested that the purified enzyme was a sin-gle protein. Though most microbial chitosanases had molecularmass in the range of 23–43 kDa, the molecular mass of thisenzyme was bigger than the reported value [19]. This significantdifference might have been caused by the cellulase structure,which has a linker combine catalytic domain and cellulose-binding domain [20]. The enzyme had an optimum pH of 5.2,temperature of 60 ◦C for chitosan hydrolysis, and had an opti-mum pH of 4.2 and temperature of 55 ◦C for CMC hydrolysis.Taking into account the differential behavior of this purifiedhydrolase in attacking �-1,4 linked polysaccharides of differ-ent chemical structures, it could be speculated that this enzymepossesses different catalytic sites for attacking the glycosidiclinkages of those two polysaccharides. The effects of DD onchitosanase activity have been described previously for enzymesfrom Penicillium islandium [21], Bacillus circulans MH-K1 [22]ahwtthpoohbtpmhacifv

A

e

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[

[

[

[

[

[

[

[

[

[

[

[

nd Bacillus sp. 7I-7S [23]. The fungal enzyme was less active inydrolyzing chitosan that less than 40% or more than 70% DD,hereas bacillus chitosanase was most active in hydrolyzing chi-

osan with a high DD. Analysis of the reaction products from chi-osan with different DD indicated that this bifunctional enzymead broad specificity for deacetylated chitosan and the majorroducts were dimmer, trimmer oligomers together with someligomers with longer chain lengths. However, a minor amountf monosaccharide was also present when chitosan underwentydrolysis for a long time. The crude enzyme split chitosan inoth exo-manner and endo-manner as indicated by the composi-ion of chitosan hydrolysates. The purified enzyme, one magicalart of the crude enzyme, split chitooligosaccharides in an exo-anner as indicated by the composition of chitooligosaccharides

ydrolysates, and had high glycosidase activity (data not shown)s well but no transglycosylation activity. This property wasonsistent with the enzyme from Myxobactor AL-1 that exhib-ted both �-1,4-glucanase and chitosanase activities. However,urther investigation is required for the enzyme bifunctional acti-ation mechanism.

cknowledgement

This project was financially supported by the National Sci-nce Foundation of China.

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