Purification and characterisation of two extremely halotolerant xylanases from a novel halophilic bacterium

The present work reports for the first time the purification and characterisation of two extremely halotolerant endo-xylanases from a novel halophilic bacterium, strain CL8. Purification of the two xylanases, Xyl 1 and 2, was achieved by anion exchange and hydrophobic interaction chromatography. The enzymes had relative molecular masses of 43 kDa and 62 kDa and pI of 5.0 and 3.4 respectively. Stimulation of activity by Ca(2+), Mn(2+), Mg(2+), Ba(2+), Li(2+), NaN(3) and isopropanol was observed. The K(m) and V(max) values determined for Xyl 1 with 4- O-methyl- d-glucuronoxylan are 5 mg/ml and 125,000 nkat/mg respectively. The corresponding values for Xyl 2 were 1 mg/ml and 143,000 nkat/mg protein. Xylobiose and xylotriose were the major end products for both endoxylanases. The xylanases were stable at pH 4-11 showing pH optima around pH 6. Xyl 1 shows maximal activity at 60 degrees C, Xyl 2 at 65 degrees C (at 4 M NaCl). The xylanases showed high temperature stability with half-lives at 60 degrees C of 97 min and 192 min respectively. Both xylanases showed optimal activity at 1 M NaCl, but substantial activity remained for both enzymes at 5 M NaCl.

Xylanase production by Penicillium canescens 10-10c in solid-state fermentation

Filamentous fungi have been widely used to produce hydrolytic enzymes for industrial applications, including xylanases, whose levels in fungi are generally much higher than those in yeast and bacteria. We evaluated the influence of carbon sources, nitrogen sources, and moisture content on xylanase production by Penicillium canescens 10-10c in solid-state fermentation. Among agricultural wastes tested (wheat bran, untreated wheat straw, treated wheat straw, beet pulp, and soja meal), untreated wheat straw gave the highest production of xylanase. Optimal initial moisture content for xylanase production was 83%. The addition of 0.4 g of xylan or easily metabolizable sugar, such as glucose and xylose, at a concentration of 2 % to wheat straw enhanced xylanase production. In solid-state fermentation, even at high concentrations of glucose or xylose (10%), catabolic repression was minimized compared to the effect observed in liquid culture. Yeast extract was the best nitrogen source among the nitrogen sources investigated: peptone, ammonium nitrate, sodium nitrate, ammonium chloride, and ammonium sulfate. A combination of yeast extract and peptone as nitrogen sources led to the best xylanase production.

Effect of dose of xylanase on bleachability of sugarcane bagasse ethanol/water pulps

Pulps obtained from the ethanol/water cooking of sugarcane bagasse were bleached with the xylanase enzyme obtained from the fungus Thermomyces lanuginosus IOC-4145 and with the commercial enzyme Cartazyme HS from Sandoz. By changing the enzyme dose from 4.3 to 36 IU/g of pulp, kappa number and viscosity were maintained when the xylanase from T. lanuginosus was used. On the other hand, by using Cartazyme HS, kappa number decreased by 17%, reaching 35.5. This pulp was further extracted with NaOH without a decrease in viscosity (10 cP), and pulp with a kappa number of 13 was obtained. Xylanases had no significant effect on the ethanol/water pulps.

Purification and characterization of ginsenoside Ra-hydrolyzing beta-D-xylosidase from Bifidobacterium breve K-110, a human intestinal anaerobic bacterium

Beta-D-Xylosidase (EC 3.2.1.37) has been purified from ginsenoside Ra-metabolizing Bifidobacterium breve K-110, which was isolated from human intestinal microflora. beta-D-Xylosidase was purified to apparent homogeneity by a combination of ammonium sulfate precipitation, QAE-cellulose, butyl-toyopearl, hydroxyapatit and Q-Sepharose column chromatographies with the final specific activity of 51.8 micromol/min/mg. Molecular weight of beta-D-xylosidase is 49 kDa by SDS-PAGE and gel filtration, which consisted of a single subunit. beta-D-Xylosidase showed optimal activity at pH 5.0 and 37 degrees C. The purified enzyme was potently inhibited by PCMS. beta-D-Xylosidase acted to the greatest extent on p-nitrophenyl-beta-D-xylopyranoside, followed by ginsenoside Ra1 and ginsenoside Ra2. This enzyme hydrolyzed xylan to xylose, but did not act on p-nitrophenyl-beta-glucopyranoside, p-nitrophenyl-beta-galactopyranoside or p-nitrophenyl-beta-D-fucopyranoside. These findings suggest that this is the first reported purification of ginsenoside-hydrolyzing beta-D-xylosidase from an anaerobic Bifidobacterium sp.

Purification and characterization of a novel cellulase-free xylanase from Acrophialophora nainiana

A beta-xylanase (XynIII) of Acrophialophora nainiana was purified to homogeneity from the culture supernatant by ultrafiltration and a combination of ion exchange and gel filtration chromatographic methods. It was optimally active at 55 degrees C and pH 6.5. XynIII had molecular masses of 27.5 and 54 kDa, as estimated by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively. The purified enzyme hydrolyzed preferentially xylan as the substrate. The half-lives of XynIII at 50 and 60 degrees C were 96 and 1 h, respectively. It was activated by L-tryptophan, dithiothreitol, 5,5-dithio-bis(2-nitrobenzoic acid, L-cysteine and beta-mercaptoethanol and strongly inhibited by N-bromosuccinimide. The presence of carbohydrate was detected in the pure XynIII.

Xylan-hydrolyzing enzyme system from Bacillus pumilus CBMAI 0008 and its effects on Eucalyptus grandis kraft pulp for pulp bleaching improvement

The extracellular productions of beta-xylanase, beta-xylosidase, beta-glucosidase, beta-mannanase, arabinosidase, alpha-glucuronidase, alpha-galactosidase and Fpase from Bacillus pumilus CBMAI 0008 were investigated with three different xylan sources as substrate. The enzymatic profiles on birchwood, Eucalyptus grandis and oat were studied at alkaline and acidic pH conditions. B. pumilus CBMAI 0008 grown on the three carbon sources produced mainly beta-xylanase. At pH 10, the levels of xylanase were 328, 160 and 136 U/ml, for birch, oat and E. grandis, respectively. beta-Mannanase production was induced on E. grandis (5 U/ml) and arabinofuranosidase on oat (5 U/ml). Although small quantities of alpha-glucuronidase had been produced at pH 10, activity at pH 4.8 was 1.5 U/ml, higher than observed for Aspergillus sp. in literature reports. Preliminary assays carried out on E. grandis kraft pulp from an industrial paper mill (RIPASA S.A. Celulose e Papel, Limeira, SP, Brazil) showed a reduction of 0.3% of chlorine use in the pulp treated with the enzymes, resulting in increased brightness, compared to conventional bleaching. The enzymes were more efficient if applied before the initial bleaching sequence, in a non-pre-oxygenated pulp.

Characterization of a Paenibacillus cell-associated xylanase with high activity on aryl-xylosides: a new subclass of family 10 xylanases

The sequence of gene xynB encoding xylanase B from Paenibacillus sp. BP-23 was determined. It revealed an open reading frame of 999 nucleotides encoding a protein of 38,561 Da. The deduced amino acid sequence of xylanase B shows that the N-terminal region of the enzyme lacks the features of a signal peptide. When the xylan-degrading system of Paenibacillus sp. BP-23 was analysed in zymograms, it revealed that xylanase B was not secreted to the extracellular medium but instead remained cell-associated, even in late stationary-phase cultures. When xynB was expressed in a Bacillus subtilis secreting host, it also remained associated with the cells. Sequence homology analysis showed that xylanase B from Paenibacillus sp. BP-23 belongs to family 10 glycosyl hydrolases, exhibiting a distinctive high homology to six xylanases of this family. The homologous enzymes were also found to be devoid of a signal peptide and seem to constitute, together with xylanase B, a separate group of enzymes. They all have two conserved amino acid regions not found in the other family 10 xylanases, and cluster in a separate group after dendrogram analysis. We propose that these enzymes constitute a new subclass of family 10 xylanases, that are cell-associated, and that hydrolyse the xylooligosaccharides resulting from extracellular xylan hydrolysis. Xylanase B shows similar specific activity on aryl-xylosides and xylans. This can be correlated to some, not yet identified, trait of catalytic activity of the enzyme on plant xylan.

Production, purification, and characterization of a low-molecular-mass xylanase from Aspergillus sp. and its application in baking

An extracellular xylanase produced by a Mexican Aspergillus strain was purified and characterized. Aspergillus sp. FP-470 was able to grow and produce extracellular xylanases on birchwood xylan, oat spelt xylan, wheat straw, and corncob, with higher production observed on corncob. The strain also produced enzymes with cellulase, amylase, and pectinase activities on this substrate. A 22-kDa endoxylanase was purified 30-fold. Optimum temperature and pH were 60 degrees C and 5.5, respectively, and isoelectric point was 9.0. The enzyme has good stability from pH 5.0 to 10.0, retaining >80% of its original activity within this range. Half-lives of 150 min at 50 degrees C and 6.5 min at 60 degrees C were found. K(m) and activation energy values were 3.8 mg/mL and 26 kJ/mol, respectively, using birchwood xylan as substrate. The enzyme showed a higher affinity for 4-O-methyl-D-glucuronoxylan with a K(m) of 1.9 mg/mL. The enzyme displayed no activity toward other polysaccharides, including cellulose. Baking trials were conducted using the crude filtrate and purified enzyme. Addition of both preparations improved bread volume. However, addition of purified endoxylanase caused a 30% increase in volume over the crude extract.

Characterisation and application of glycanases secreted by Aspergillus terreus CCMI 498 and Trichoderma viride CCMI 84 for enzymatic deinking of mixed office wastepaper

Two enzymatic extracts obtained from xylan-grown Aspergillus terreus CCMI 498 and cellulose-grown Trichoderma viride CCMI 84 were characterised for different glycanase activities. Both strains produce extracellular endoxylanase and endoglucanase enzymes. The enzymes optimal activity was found in the temperature range of 45-60 degrees C. Endoglucanase systems show identical activity profiles towards temperature, regardless of the strain and inducing substrate. Conversely, the endoxylanases produced by both strains showed maximal activity at different pH values (from 4.5 to 5.5), being the more acidic xylanase produced by T. viride grown on cellulose. The endoglucanase activities have an optimum pH at 4.5-5.0. The endoxylanase and endoglucanase activities exhibited high stability at 50 degrees C and pH 5.0. Mannanase, beta-xylosidase, and amylase activities were also found, being the first two activities only present for T. viride extract. These two enzymatic extracts were used for mixed office wastepaper (MOW) deinking. When the enzymatic extract from T. viride was used, a further increase of 24% in ink removal was obtained by comparison with the control. Both enzymes contributed to the improvement of the paper strength properties and the obtained results clearly indicate that the effective use of enzymes for deinking can also contribute to the pulp and paper properties improvement.

Enzymatic synthesis of beta-xylanase substrates: transglycosylation reactions of the beta-xylosidase from Aspergillus sp

A beta-D-xylosidase with molecular mass of 250+/-5 kDa consisting of two identical subunits was purified to homogeneity from a cultural filtrate of Aspergillus sp. The enzyme manifested high transglycosylation activity in transxylosylation with p-nitrophenyl beta-D-xylopyranoside (PNP-X) as substrate, resulting in regio- and stereoselective synthesis of p-nitrophenyl (PNP) beta-(1-->4)-D-xylooligosaccharides with dp 2-7. All transfer products were isolated from the reaction mixtures by HPLC and their structures established by electrospray mass spectrometry and 1H and 13C NMR spectroscopy. The glycosides synthesised, beta-Xyl-1-->(4-beta-Xyl-1-->)(n)4-beta-Xyl-OC6H4NO2-p (n=1-5), were tested as chromogenic substrates for family 10 beta-xylanase from Aspergillus orizae (XynA) and family 11 beta-xylanase I from Trichoderma reesei (XynT) by reversed-phase HPLC and UV-spectroscopy techniques. The action pattern of XynA against the foregoing PNP beta-(1-->4)-D-xylooligosaccharides differed from that of XynT in that the latter released PNP mainly from short PNP xylosides (dp 2-3) while the former liberated PNP from the entire set of substrates synthesised.

Simultaneous measurement of protein one-bond and two-bond nitrogen-carbon coupling constants using an internally referenced quantitative J-correlated [(15)N,(1)H]-TROSY-HNC experiment

A quantitative J-correlation pulse sequence is described that allows simultaneous determination of one-bond and two-bond nitrogen-carbon coupling constants for protonated or deuterated proteins. Coupling constants are calculated from volume ratios between cross peaks and reference axial peaks observed in a single 3D spectrum. Accurate backbone (1)J(NC'), (1)J(NCalpha), and (2)J(NCalpha) coupling constants are obtained for the two [(15)N;(13)C]-labeled, medium-sized proteins flavodoxin and xylanase and for the [(2)H;(15)N;(13)C]-labeled, large protein DFPase. A dependence of one-bond and two-bond J(NCalpha) values on protein backbone psi torsion angles is readily apparent, in agreement with previously found correlations. In addition, the experiment is performed on isotropic as well as aligned protein to measure associated (15)N-(13)C residual dipolar couplings.

Production of recombinant bleaching enzymes from thermophilic microorganisms in fungal hosts

Cost-effective production of enzymes for industrial processes makes the appropriate selection of the host-vector expression system critical. We have developed two systems for the bulk production of bleaching enzymes from thermophiles. Kluyveromyces lactis has been developed as a secretion host employing expression vectors based on the 2mu-like plasmid pKD1 of Kluyveromyces drosophilarium. Our second system involves the filamentous fungus Trichoderma reesei. Fusion and nonfusion vectors have been constructed using the strong cellobiohydrolase 1 (cbh1) promoter. The KEX2 protease cleavage site and a 6 x HIS-tag have been incorporated to facilitate both cleavage and purification of the mature foreign proteins.

Macroaffinity ligand-facilitated three-phase partitioning (MLFTPP) for purification of xylanase

It is shown that eudragit S-100, a copolymer of methylacrylic acid and methylmethacrylate, undergoes three-phase partitioning. It was found that 95% eudragit S-100 could be recovered as the interfacial precipitate by using 30% (w/v) ammonium sulfate, 1:1 ratio of t-butanol to polymer solution at 40 degrees C. Three-phase partitioning of proteins uses simultaneous addition of ammonium sulfate and t-butanol to precipitate proteins in an interfacial layer separating the aqueous phase and organic solvent. Exploiting the affinity of xylanases towards eudragit S-100, it was possible to purify xylanase from Aspergillus niger; 60% recovery of activity with 95-fold purification could be obtained by this process. The purified enzyme showed A single band on SDS-PAGE. The technique shows promise to develop into a general method that could be termed "macroaffinity ligand-facilitated three-phase partitioning (MLFTPP).

Biotechnology of microbial xylanases: enzymology, molecular biology, and application

Xylanases are hydrolases depolymerizing the plant cell wall component xylan, the second most abundant polysaccharide. The molecular structure and hydrolytic pattern of xylanases have been reported extensively and the mechanism of hydrolysis has also been proposed. There are several models for the gene regulation of which this article could add to the wealth of knowledge. Future work on the application of these enzymes in the paper and pulp, food industry, in environmental science, that is, bio-fueling, effluent treatment, and agro-waste treatment, etc. require a complete understanding of the functional and genetic significance of the xylanases. However, the thrust area has been identified as the paper and pulp industry. The major problem in the field of paper bleaching is the removal of lignin and its derivatives, which are linked to cellulose and xylan. Xylanases are more suitable in the paper and pulp industry than lignin-degrading systems.

Characterization of alkaline thermoactive cellulase-free xylanases from alkalophilic Bacillus (NCL 87-6-10)

Two alkaline xylanases designated as "A" and "C", respectively, were isolated from the culture filtrates of the alkalophilic Bacillus grown on a wheat bran-yeast extract medium. The two xylanases occurred in the culture filtrate in a ratio of 10:90. These xylanases were purified to homogeneity on a CM-Sephadex matrix followed by further separation of Xylanase "A" on a phenyl sepharose column and preparative electrophoresis. The two xylanases differed considerably in their physico-chemical properties, kinetics and in their mode of action. Xylanase "C" had a molecular weight of 25,000 as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and was a cationic protein with a pI of 8.9. In contrast xylanase "A" had a molecular weight of 45,000 with a pI of 5.3. The two xylanases showed distinct differences in their hydrolysis pattern. Xylanase "A" produced comparatively larger amounts of small molecular weight oligosaccharides and xylose namely xylotriose (X(3)), xylobiose (X(2)) and xylose even in the initial stages of hydrolysis (2 and 5 h) while xylanase "C" produced negligible amounts of X(2) and no xylose for the same period of incubation. At 24 h only traces of xylose was produced by xylanase "C" while substantial amounts of the monomer was produced by xylanase A in 24 h. Xylanase "A" had a broad pH optimum ranging from pH 6.0-10.0 at 40-60 degrees C while xylanase "C" had an optimum pH of 8.0 at 40-60 degrees C. Xylanases "A" and "C" differed in their K(m) and V(max) values. Xylanase "A" had a K(m) of 1.67 mg/ml and a V(max) of 3.85 x 10(2) micromol/ml/min, whereas xylanase "C" had a K(m) of 10 mg/ml and a V(max) of 1.43 x 10(4) micromol/ml/min.

Properties and application of a partially purified alkaline xylanase from an alkalophilic fungus Aspergillus nidulans KK-99

An alkalophilic Aspergillus nidulans KK-99 produced an alkaline, thermostable xylanase (40 IU/ml) in a basal medium supplemented with wheat bran (2% w/v) and KNO3 (at 0.15% N) pH 10.0 and 37 degrees C. The partially purified xylanase was optimally active at pH 8.0 and 55 degrees C. The xylanase was stable in a broad pH range of 4.0-9.5 for 1 h at 55 degrees C, retaining more than 80% of its activity. The enzyme exhibited greater binding affinity for xylan from hardwood than from softwood. The xylanase activity was stimulated (+25%) by Na+ and Fe2+ and was strongly inhibited (maximum by 70%) by Tween-20, 40, 60, SDS, acetic anhydride, phenylmethane sulphonyl fluoride, Triton-X-100. The xylanase dose of 1.0 IU/g dry weight pulp gave optimum bleach boosting of Kraft pulp at pH 8.0 and temperature 55 degrees C for 3 h reaction time.

A novel family 8 xylanase, functional and physicochemical characterization

Xylanases are generally classified into glycosyl hydrolase families 10 and 11 and are found to frequently have an inverse relationship between their pI and molecular mass values. However, we have isolated a psychrophilic xylanase that belongs to family 8 and which has both a high pI and high molecular mass. This novel xylanase, isolated from the Antarctic bacterium Pseudoalteromonas haloplanktis, is not homologous to family 10 or 11 enzymes but has 20-30% identity with family 8 members. NMR analysis shows that this enzyme hydrolyzes with inversion of anomeric configuration, in contrast to other known xylanases which are retaining. No cellulase, chitosanase or lichenase activity was detected. It appears to be functionally similar to family 11 xylanases. It hydrolyzes xylan to principally xylotriose and xylotetraose and is most active on long chain xylo-oligosaccharides. Kinetic studies indicate that it has a large substrate binding cleft, containing at least six xylose-binding subsites. Typical psychrophilic characteristics of a high catalytic activity at low temperatures and low thermal stability are observed. An evolutionary tree of family 8 enzymes revealed the presence of six distinct clusters. Indeed classification in family 8 would suggest an (alpha/alpha)(6) fold, distinct from that of other currently known xylanases.

[Isolation of endo-1,4-beta-xylanase from Geotrichum candidum 3C with various ability of sorption on an insoluble substrate]

Culture liquid from Geotrichum candidum 3C was shown to contain three endoxylanase types: endoxylanase I that binds to cellulose, endoxylanase II that sorbs to insoluble xylan, and endoxylanase III that cannot sorb to dissoluble substrate. The catalytic and substrate-binding domains of endoxylanase II were isolated.

A family 11 xylanase from Penicillium funiculosum is strongly inhibited by three wheat xylanase inhibitors

Steady-state kinetic approaches were used to investigate the binding of a novel Penicillium funiculosum xylanase, XYNC, with three known xylanase inhibitor proteins from wheat (Triticum aestivum). The xylanase gene (xynC) was cloned from a P. funiculosum genomic library and the deduced amino acid sequence of XYNC exhibited high sequence similarity with fungal family 11 xylanases. xynC was overexpressed in P. funiculosum and the product (XYNC: M(r)=23.6 kDa; pI=3.7) purified and shown to efficiently degrade birchwood xylan [K(m)=0.47% w/v, Vmax=2540 micromol xylose min(-1) (mg protein)(-1) at pH 5.5 and 30 degrees C] and soluble wheat arabinoxylans [K(m)=1.45% w/v, Vmax=7190 micromol xylose min(-1) mg protein)(-1) at pH 5.5 and 30 degrees C]. The xylanase activity of XYNC was inhibited strongly by three xylanase inhibitor proteins from wheat; XIP-I, TAXI I and TAXI II. The inhibition for each was competitive, with very tight binding (K(i)=3.4, 16 and 17 nM, respectively) equivalent to free energy changes (deltaG degrees ) of -49, -45 and -45 kJ mol(-1). This is the first report describing a xylanase that is inhibited by all three wheat xylanase inhibitor proteins described to date.

Screening of variables in beta-xylosidase recovery using cetyl trimethyl ammonium bromide reversed micelles

Beta-xylosidase recovery by micelles using cetyl trimethyl ammonium bromide (CTAB) cationic surfactant was verified under different experimental conditions. A 2(5-1) fractional factorial design with center points was employed to verify the influence of the following factors on enzyme extraction: pH (x1), CTAB concentration (x2), electrical conductivity (x3), hexanol concentration (x4), and butanol concentration (x). Statistical analysis of the results shows that of the five variables studied only hexanol and electrical conductivity did not have significant effects on the recovery of beta-xylosidase. The other factors had significant effects in increasing order: (x1) > (x2) > (x5). The model predicts a recovery value of about 45%, which is similar to that obtained experimentally (43.5%).

A xylanase from roots of sanchi ginseng (Panax notoginseng) with inhibitory effects on human immunodeficiency virus-1 reverse transcriptase

A xylanase with a molecular weight of 15 kDa, which is lower than those of previously reported xylanases, was isolated from the roots of the medicinal herb Panax notoginseng. The xylanase exhibits a temperature optimum of 50 degrees C and a pH optimum between 5 and 6. It inhibits HIV-1 reverse transcriptase with an IC(50) of 10 microM, but does not affect translation in a cell-free rabbit reticulocyte system when tested up to 70 microM. The enzyme is adsorbed on CM-cellulose, Affi-gel blue gel and Mono S. Previously xylanases have been isolated from seeds and not from roots, and have not been demonstrated to inhibit HIV-1 reverse transcriptase.

Purification and characterization of two endo-1,4-beta-xylanases and a 3-xylosidase from phlebia radiata

Two different endo-1,4-beta-xylanases, designated XA-1 and XA-2, and one beta-xylosidase (XD-1) have been purified by column chromatography to apparent homogeneity from the extracellular culture fluid of Phlebia radiata grown on wheat bran. The molecular masses of XA- 1, XA-2 and XD-1 were 18.6, 15.8 kDa, and 27 kDa, respectively. The isoelectric points for the xylanases were 6.7 and 4.1 and for the xylosidase - 5.9. The Km and Vmax values with larchwood xylan as substrate were 4.86 mg ml(-1) and 0.17 micromol min(-1) mg(-1) for XA-1; 2.7 mg ml(-1) and 3.91 micromol min(-1) mg(-1) for XA-2, whereas with pNPK as a substrate the Km and Vmax for XD-1 was 1.28 mM and 7.41 micromol min(-1) mg(-1). All the above enzymes are glycoproteins and the carbohydrate contents are for- XA-1 and XA-2 (6.70%, 3.58%) and for XD-1 (12.8%). Endoxylanase XA-1 and XA-2 were not able to release arabinose from rye arabinoxylan and birch xylan. Both enzymes were endo-acting, as revealed by their hydrolysis product profiles on xylan substrates.

Enzymatic properties of a neutral endo-1,3(4)-beta-xylanase Xyl II from Bacillus subtilis

A Bacillus sp. CCMI 966, characterised as Bacillus subtilis, has a duplication time of about 24 min. It produces at least two extracellular xylanases, Xyl I and Xyl II. The extracellular xylanase activity seems to be strongly correlated with the biomass growth profile. The Xyl II isoenzyme was purified by ammonium sulphate precipitation and anionic exchange chromatography, with a purification factor of 8.3. The molecular weight of the isoenzyme was estimated by SDS-PAGE revealing that Xyl II is a multimeric enzyme with a catalytic subunit of about 20 kDa. Under non-denaturing conditions, a molecular weight of about 340 kDa was obtained by native PAGE gel and of 20 kDa by gel filtration chromatography. The enzyme showed an optimum pH and temperature of 6.0 at 60 degrees C. Xyl II was stable at 40 degrees C for 180 min at pH 6.0. The specificity of Xyl II for different substrates was evaluated. Xyl II presents a higher affinity towards OSX, with a K(m) of 1.56 g l(-1) and showed the ability to hydrolyse laminarin, with a K(m) of 1.02 g l(-1). Xylotetraose is the main product of xylan degradation. The Xyl II ability for binding to cellulose and/or xylan was also studied.

A beta-glucosidase/xylosidase from the phytopathogenic oomycete, Phytophthora infestans

An 85-kDa beta-glucosidase/xylosidase (BGX1) was purified from the axenically grown phytopathogenic oomycete, Phytophthora infestans. The bgx1 gene encodes a predicted 61-kDa protein product which, upon removal of a 21 amino acid leader peptide, accumulates in the apoplastic space. Extensive N-mannosylation accounts for part of the observed molecular mass difference. BGX1 belongs to family 30 of the glycoside hydrolases and is the first such oomycete enzyme deposited in public databases. The bgx1 gene was found in various Phytophthora species, but is apparently absent in species of the related genus, Pythium. Despite significant sequence similarity to human and murine lysosomal glucosylceramidases, BGX1 demonstrated neither glucocerebroside nor galactocerebroside-hydrolyzing activity. The native enzyme exhibited glucohydrolytic activity towards 4-methylumbelliferyl (4-MU) beta-D-glucopyranoside and, to lesser extent, towards 4-MU-D-xylopyranoside, but not towards 4-MU-beta-D-glucopyranoside. BGX1 did not hydrolyze carboxymethyl cellulose, cellotetraose, chitosan or xylan, suggesting high substrate specificity and/or specific cofactor requirements for enzymatic activity.

The performance of fungal xylan-degrading enzyme preparations in elemental chlorine-free bleaching for Eucalyptus pulp

Cellulase-free xylan-degrading enzyme preparations from Acrophialophora nainiana, Humicola grisea var. thermoidea and two Trichoderma harzianum strains were used as bleaching agents for Eucalyptus kraft pulp, prior to a chlorine dioxide and alkaline bleaching sequence. In comparison to the control sequence (performed without xylanase pretreatment), the sequence incorporating enzyme treatment was more effective. Removal of residual lignin was indicated by a reduction in kappa number. Overall, enzyme preparations from T. harzianum were marginally more effective in reducing pulp viscosity and chlorine chemical consumption and improving the brightness of the kraft pulp. However, the highest reduction in pulp viscosity was mediated by the xylanase preparation from A. nainiana. Xylanase pretreatment compares very favorably with that of chemical pulping.