Mutational and crystallographic analyses of the active site residues of the Bacillus circulans xylanase

Using site-directed mutagenesis we have investigated the catalytic residues in a xylanase from Bacillus circulans. Analysis of the mutants E78D and E172D indicated that mutations in these conserved residues do not grossly alter the structure of the enzyme and that these residues participate in the catalytic mechanism. We have now determined the crystal structure of an enzyme-substrate complex to 108 A resolution using a catalytically incompetent mutant (E172C). In addition to the catalytic residues, Glu 78 and Glu 172, we have identified 2 tyrosine residues, Tyr 69 and Tyr 80, which likely function in substrate binding, and an arginine residue, Arg 112, which plays an important role in the active site of this enzyme. On the basis of our work we would propose that Glu 78 is the nucleophile and that Glu 172 is the acid-base catalyst in the reaction.

Chemical modification of xylanase from alkalothermophilic Bacillus species: evidence for essential carboxyl group

The role of carboxyl group in the catalytic action of xylanase (M(r) 35,000) from an alkalothermophilic Bacillus sp. was delineated through kinetic and chemical modification studies using Woodward's Reagent K. The kinetics of inactivation indicated that one carboxyl residue was essential for the xylanase activity with a second order rate constant of 3300 M-1 min-1. The spectrophotometric analysis at 340 nm revealed that the inhibition was correlated with modification of 24 carboxyl residues. In the presence of protecting ligand, modification of one carboxyl group was prevented. The pH profile showed apparent pK values of 5.2 and 6.4 for the free enzyme and 4.9 and 6.9 for enzyme-substrate complex. The pH dependence of inactivation was consistent with the modification of carboxyl group. The kinetic analysis of the modified enzyme showed similar Km and lower kcat values than the native enzyme indicating that catalytic hydrolysis and not the substrate binding was affected by chemical modification. The chemical modification of xylanase from alkalothermophilic Bacillus revealed the presence of tryptophans in the active site (Deshpande, V, Hinge, J. and Rao, M. (1990) Biochim. Biophys. Acta 1041, 172-177). This finding and present studies demonstrated the experimental evidence for the participation of carboxyl as well as tryptophan groups as essential residues of xylanase from alkalothermophilic Bacillus sp.

Identification of a glutamate residue at the active site of xylanase A from Schizophyllum commune

The xylanase A (endo-1,4-beta-D-xylan xylanhydrolase) of the basidiomycete Schizophyllum commune was treated with the powerful carboxylate-modifying reagent 1-(4-azonia-4,4-dimethyl-pentyl)-3-ethylcarbodiimide iodide (EAC) in the presence of substrate. This treatment was followed by complete inactivation of the enzyme with [14c]EAC after the removal of excess reagent and protecting ligand. The inactivated enzyme was digested with endoproteinase Arg-C or trypsin, and peptides were separated and purified using reverse-phase high-performance liquid chromatography. Following sub-digestion of individual radioactive peptides with staphylococcal V8 protease and endoproteinase Lys-C, amino acid composition analysis and sequencing analysis revealed that the [14C]EAC label was bound exclusively to Glu87. Comparison of the primary sequences of related xylanase with that of xylanase A revealed that Glu87 is a highly conserved residue. Based on this similarity and the mechanism of carbodiimide action, Glu87 is proposed to act as the nucleophile in the catalytic mechanism of xylanase A. The possible environment of the putative catalytic glutamate residue was explored using hydrophobic-cluster analysis and secondary-structure prediction based on the primary sequence of xylanase.

Crystallization and preliminary diffraction analysis of the catalytic domain of xylanase Z from Clostridium thermocellum

The catalytic domain of a thermostable xylanase from Clostridium thermocellum has been expressed in Escherichia coli and crystallized from a polyethylene glycol 2000 solution by the hanging drop method. Crystals belong to the triclinic space group P1 with cell dimensions a = 46.8 A, b = 50.8 A, c = 70.3 A, alpha = 100.7 degrees, beta = 83.8 degrees, gamma = 101.6 degrees, and two molecules in the unit cell. These crystals diffract X-rays to at least 1.8 A resolution and are suitable for high-resolution X-ray analysis.

Alteration of asparagine-linked glycosylation in serum transferrin of patients with hepatocellular carcinoma

The asparagine-linked sugar chains in serum transferrin purified from patients with hepatocellular carcinoma (n = 13), healthy individuals (n = 5) and patients with liver cirrhosis (n = 6) were compared. Sugar chains released with N-glycanase from desialylated and pepsin-digested transferrin were derivatized by reductive pyridylamination. Analysis of the sugar chains by high performance liquid chromatography in combination with exoglycosidase digestion revealed an increase of a biantennary complex-type sugar chain with a fucosylated trimannosyl core; Gal beta 1-4GlcNAc beta 1-2Man alpha 1-6(Gal beta 1-4GlcNAc beta 1-2Man alpha 1-3) Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-6)GlcNAc in 7 of 13 cancer patients and an increase of a sugar chain with a fucosylated trimannosyl core and bisecting N-acetylglucosamine; Gal beta 1-4GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-4) (Gal beta 1-4GlcNAc beta 1-2Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-6)GlcNAc in one of the 13 cancer patients. Further, the fucosylated alteration of the sugar chain was detected also in alpha 1-antitrypsin, hemopexin, alpha 1-acid glycoprotein and alpha 2-HS glycoprotein from one of the patients with increased fucosylated transferrin.

Horseshoe crab (1,3)-beta-D-glucan-sensitive coagulation factor G. A serine protease zymogen heterodimer with similarities to beta-glucan-binding proteins

Horseshoe crab factor G is an intracellular serine protease zymogen that initiates the (1,3)-beta-D-glucan-sensitive hemolymph clotting pathway. Unlike other known serine protease zymogens, which are composed of a single subunit, factor G consists of two distinct subunits, alpha and beta, which are autocatalytically converted to active factor G in the presence of (1,3)-beta-D-glucan. We have now cloned and sequenced cDNAs encoding both subunits of factor G. The subunits are derived from separate mRNA species and thus encoded by different genes. Subunit beta is a serine protease zymogen which consists of 278 residues with a calculated molecular mass of 30,846 Da; it exhibits homology to the serine protease domain of horseshoe crab factor B. Subunit alpha, on the other hand, is a new type of mosaic protein with intriguing features. The mature protein consists of 654 residues with a calculated molecular mass of 73,916 Da. The NH2-terminal portion of this subunit is similar to bacterial beta-1,3-glucanases. Its 126 amino acid COOH terminus exhibits a repetitive sequence having partial homology to xylanases. Between these regions are three repeating units of 47 amino acids, whose similarity to carbohydrate-binding proteins suggests that these may be the (1,3)-beta-D-glucan-binding domain(s) of factor G. Factor G, thus, is a structurally unique heterodimeric serine protease zymogen and as such may represent a new class of active defense proteins.

alpha-L-arabinofuranosidase production by Aspergillus nidulans

The effects of some physico-chemical parameters on production of extracellular alpha-L-arabinofuranosidase by Aspergillus nidulans were examined. Highest levels of alpha-L-arabinofuranosidase were generated with cultures grown on 1% (w/v) purified beet pulp arabinan at 30 degrees C and at an initial pH of 7.0. The enzyme was shown to be very sensitive to the action of proteases. Zymogram overlay of a protein profile obtained by SDS-PAGE revealed the occurrence of a band (M(r) 36,000) exhibiting alpha-L-arabinofuranosidase activity. The isoelectric pH of the enzyme lay near 4.3. Temperature and pH optima for the activity of crude alpha-L-arabinofuranosidase preparations were 55 degrees C and 5.5, respectively. Enzyme activity was greatly reduced by thiol reagents such as Hg2+ and p-hydroxymercuribenzoate and showed a Km value of 2.7 mM on p-nitrophenyl alpha-L-arabinofuranoside as substrate.

Different effects of N-glycosylation on the thermostability of highly homologous bacterial (1,3-1,4)-beta-glucanases secreted from yeast

Genes encoding Bacillus amyloliquefaciens (1,3-1,4)-beta-glucanase (AMY), B. macerans (1,3-1,4)-beta-glucanase (MAC), and a series of hybrid enzymes containing N-terminal sequence segments of different length derived from AMY with the remaining C-terminal segment derived from MAC, were expressed in Saccharomyces cerevisiae. The cells secreted active enzyme into the medium. While the quantity of N-glycan linked to the different enzymes was similar, pronounced differences in thermotolerance were observed when the glycosylated enzymes were compared with the unglycosylated counterparts produced in Escherichia coli. Glycosylated AMY and hybrid enzyme H(A16-M), consisting of 16 N-terminal amino acids derived from AMY with the remaining C-terminal segment from MAC, exhibited a 7.5- and 1.6-fold increase in half-life at 70 degrees C, pH 6.0. N-terminal sequencing established that only two out of three sites for potential N-glycosylation of H(A16-M) secreted from yeast were actually glycosylated. Removal of N-glycans by endoglycosidase H and peptide:N-glycosidase F from H(A16-M) resulted in a 16- and 133-fold decrease of thermostability, demonstrating that N-glycans are a major determinant for the resistance of this enzyme to thermal inactivation. Glycosylated MAC and hybrid enzymes H(A36-M), H(A107-M) and H(A152-M) had increased thermostability but hybrid enzyme H(A78-M) was less thermostable. N-Glycosylation thus changes thermostability of (1,3-1,4)-beta-glucanases with similar primary structure in a variable, so far unpredictable way.

Molecular genetic analysis of the pullulanase B gene of Bacillus acidopullulyticus

A fragment from Bacillus acidopullulyticus strain 294-16 encoding a pullulanase activity has been cloned into Bacillus subtilis. The nucleotide sequence of the 3972 base pairs (bp) fragment has been determined and shown to include only one complete open reading frame (ORF) of 863 codons. The deduced amino acid sequence of this ORF, denoted pulB, shows homology to a number of amylolytic enzymes. Primary and secondary structure analysis indicates that the central region of the protein forms the catalytic domain in a characteristic (beta/alpha)8 barrel. Three carboxylic acid residues essential for catalysis were identified. Regions within the catalytic domain proposed to be involved in substrate binding have been identified by homology.

Comparative amino acid sequence analysis of Thermotoga maritima beta-glucosidase (BglA) deduced from the nucleotide sequence of the gene indicates distant relationship between beta-glucosidases of the BGA family and other families of beta-1,4-glycosyl hydrolases

The primary structure of the bglA gene region encoding a beta-glucosidase of Thermotoga maritima strain MSB8 was determined. The bglA gene has the potential to code for a polypeptide of 446 amino acids with a predicted molecular mass of 51,545 Da. The T. maritima beta-glucosidase (BglA) was overexpressed in E. coli at a level comprising approximately 15-20% of soluble cellular protein. Based on its amino acid sequence, as deduced from the nucleotide sequence of the gene, BglA can be classified as a broad-specificity beta-glucosidase and as a member of the beta-glucosidase family BGA, in agreement with the results of enzymatic characterization of the recombinant protein. Comparative sequence analysis revealed distant amino acid sequence similarities between BGA family beta-glucosidases, a beta-xylosidase, beta-1,4-glycanases of the enzyme family F (mostly xylanases), and other families of beta-1,4-glycosyl hydrolases. This result indicates that BGA beta-glucosidases may comprise one enzyme family within a large 'enzyme order' of retaining beta-glycosyl hydrolases, and that the members of these enzyme groups may be inter-related at the level of active site architecture and perhaps even on the level of overall three-dimensional fold.

An internal cellulose-binding domain mediates adsorption of an engineered bifunctional xylanase/cellulase

A chimeric xylanase/endoglucanase (XynCenA) with an internal cellulose-binding domain was constructed by fusing the Bacillus subtilis xyn gene fragment to the 5'-end of the Cellulomonas fimi cenA. A polyhistidine-encoding sequence was also fused to the 5'-end of the xyn gene. The gene fusion was overexpressed in Escherichia coli and the fusion polypeptide purified from the cell extracts using the polyhistidine tail. The hybrid protein behaved like the parental endoglucanase or xylanase when assayed on a number of soluble and insoluble cellulosic substrates or xylans. The presence of two distinct active sites and the internal cellulose-binding domain did not significantly affect the hydrolysis of any of these substrates. However, the fusion protein exhibited a strong affinity for both microcrystalline cellulose (Avicel) and regenerated chitin. Like the parental endoglucanase, bound XynCenA could not be eluted from these polysaccharides with either low or high salt buffer or distilled water. More stringent conditions, such as 1% SDS or 8 M guanidinium hydrochloride, fully desorbed the protein. The fusion protein did not adsorb significantly to insoluble xylan.

Hydrolysis of glycosylpyridinium ions by anomeric-configuration-inverting glycosidases

The hydrolyses of five beta-D-xylopyranosylpyridinium ions by the beta-D-xylosidase of Bacillus pumilus proceed with kcat values 10(8)-10(9)-fold larger than the rates of spontaneous hydrolysis of the same compounds. Log(kcat) values correlate well with aglycon pK(a) [B1g(V) = -0.52, r = 0.99], whereas the correlation of log(kcat/Km) is poor [r = 0.77; beta 1g(V/K) = approximately -0.6]. The (1-->3)-beta-D-glucanase of Sporotrichum dimorphosporum hydrolyses 4-bromo-2-(beta-D-glucopyranosyl)isoquinolinium ion with a rate enhancement of 10(8). The amyloglucosidase II of Aspergillus niger hydrolyses three alpha-D-glucopyranosylpyridinium ions with rate enhancements of 10(5)-10(8). The efficient hydrolysis of glycosylpyridinium ions by these three inverting glycosidases, the catalytic mechanism of which is unlikely to involve a nucleophile from the enzyme, makes it improbable that the hydrolysis of glycosylpyridinium ions by retaining glycosidases, discovered some years ago, is initiated by addition of a catalytic nucleophilic carboxylate group of the enzyme to the pyridinium ring.

Structure of the N-linked oligosaccharides that show the complete loss of alpha-1,6-polymannose outer chain from och1, och1 mnn1, and och1 mnn1 alg3 mutants of Saccharomyces cerevisiae

The periplasmic invertase was purified from Saccharomyces cerevisiae och1::LEU2 disruptant cells (delta och1), which have a defect in elongation of the outer chain attached to the N-linked core oligosaccharides (Nakayama, K., Nagasu, T., Shimma, Y., Kuromatsu, J., and Jigami, Y. (1992) EMBO J. 11, 2511-2519). Structural analysis of the pyridylaminated (PA) neutral oligosaccharides released by hydrazinolysis and N-acetylation confirmed that the och1 mutation causes a complete loss of the alpha-1,6-polymannose outer chain, although the PA oligosaccharides (Man9GlcNAc2-PA and Man10GlcNAc2-PA), in which one or two alpha-1,3-linked mannose(s) attached to the endoplasmic reticulumn (ER)-form core oligosaccharide (Man8GlcNAc2) were also detected. Analysis of the delta och1 mnn1 strain oligosaccharides released from total cell mannoprotein revealed that the delta och1 mnn1 mutant eliminates the alpha-1,3-mannose attached to the core and accumulates predominantly a single ER-form oligosaccharide species (Man8GlcNAc2), suggesting a potential use of this strain as a host cell to produce glycoproteins containing mammalian high mannose type oligosaccharides. The delta och1 mnn1 alg3 mutants accumulated Man5GlcNAc2 and Man8GlcNAc2 in total cell mannoprotein, confirming the lack of outer chain addition to the incomplete corelike oligosaccharide and the leaky phenotype of the alg3 mutation. All the results suggest that the OCH1 gene encodes an alpha-1,6-mannosyltransferase that is functional in the initiation of alpha-1,6-polymannose outer chain addition to the N-linked core oligosaccharide (Man5GlcNAc2 and Man8GlcNAc2) in yeast.

Crystallization and preliminary X-ray studies on the core proteins of cellobiohydrolase I and endoglucanase I from Trichoderma reesei

The catalytic core domains of cellobiohydrolase I (CBHI) and endoglucanase I (EGI) from Trichoderma reesei have been crystallized using the hanging drop vapour diffusion method. In the case of CBHI, use of polyethylene glycol 20,000, and calcium chloride at low pH produced good quality single crystals suitable for X-ray studies. The crystals belong to a primitive orthorhombic space group with unit cell dimensions a = 84.0 A, b = 86.2 A, c = 111.8 A, and diffract beyond 2.0 A resolution. Bipyramidal crystals of EGI core were grown from ammonium sulphate at pH 7.5. The crystals are tetragonal, either P4(1)22 or the enantiomorph P4(3)22, with cell dimensions a = b = 101.8 A and c = 198.0 A, and at best diffract to a resolution of 2.5 A.

Crystallization and preliminary X-ray analysis of (1,3)- and (1,3;1,4)-beta-D-glucanases from germinating barley

(1,3)-beta-D-Glucanase isoenzyme GII and (1,3;1,4)-beta-D-glucanase isoenzyme EII from barley have been crystallized by the hanging drop method in the presence of ammonium sulphate. The crystals of the (1,3)-beta-D-glucanase, which diffract to about 1.8 A resolution, belong to the trigonal space group P3(1)2(1)2 (or P3(2)2(1)2) with cell constants a = b = 86.9 A, c = 156.0 A and contain two molecules in the asymmetric unit. The crystals of the (1,3;1,4)-beta-D-glucanase which diffract to better than 1.8 A resolution, belong to the tetragonal space group P4(3)2(1)2 (or P4(1)2(1)2) with cell constants a = b = 87.4 A, c = 109.5 A and contain one molecule in the asymmetric unit.

Cloning and characterization of the abfB gene coding for the major alpha-L-arabinofuranosidase (ABF B) of Aspergillus niger

Based on amino-acid sequence data from Aspergillus niger alpha-L-arabinofuranosidase B (ABF B), and cyanogen bromide fragments derived thereof, deoxyoligonucleotide mixtures were designed to be employed as primers in a polymerase chain reaction (PCR) on A. niger genomic DNA. This resulted in amplification of three related PCR products. The abfB gene encoding ABF B was isolated from a genomic library using such an amplification product as a probe. A 5.1-kb BamHI fragment was subcloned to result in plasmid pIM991. Upon introduction by co-transformation into both A. niger and A. nidulans uridine auxotrophic strains, pIM991 was shown to contain the functional gene since prototrophic transformants overproduced ABF B upon growth on the inducing carbon source sugar beet pulp. A plate assay was developed enabling quick selection of ABF B-overproducing transformants. The sequence of a 4122-bp long BamHI/SstI fragment was determined. The abfB gene does not contain introns and codes for a protein of 499 amino acids. The mature ABF B, 481 amino acids in length, has a deduced molecular weight of 50.7 kDa. A. niger abfB is the first eukaryotic gene encoding an ABF to be characterized.

Molecular cloning and physiological analysis of an invertase isoenzyme in Helianthus tissues

A soluble acid invertase activity isolated from Helianthus tuberosus (Jerusalem artichoke) shoots and analyzed by immunochromatography using polyclonal yeast antibodies, represents around 5% of the total invertase activity. This invertase isoenzyme was also isolated from dormant tuber parenchyma. In these partially dormant tissues, the specific activity of this isoenzyme is low suggesting a partial inactivation of the invertase molecules. Polyacrylamide gel electrophoresis of immunopurified fractions yields similar levels of the 58 kDa polypeptide both in shoots and dormant tubers, but with much lower activity of the enzyme in the tubers. A cDNA library was constructed in pUEX 1 from poly (A)+ RNA extracted from Jerusalem artichoke tubers. This library was screened for invertase using (i) a Bacillus subtilis invertase DNA probe and (ii) anti-yeast invertase antibodies. A recombinant clone of approximately 1.8 kb size was selected by these two methods. Using Northern blots, a temporal sequence in the expression of invertase gene was observed during the breaking of dormancy with the main level after 8 weeks of cold treatment at 4 degrees C. A 2.5 kb transcript was detected, translation of which would yield a 97 kDa polypeptide representing the precursor of Jerusalem artichoke invertase.

Starch- and glycogen-debranching and branching enzymes: prediction of structural features of the catalytic (beta/alpha)8-barrel domain and evolutionary relationship to other amylolytic enzymes

Sequence alignment and structure prediction are used to locate catalytic alpha-amylase-type (beta/alpha)8-barrel domains and the positions of their beta-strands and alpha-helices in isoamylase, pullulanase, neopullulanase, alpha-amylase-pullulanase, dextran glucosidase, branching enzyme, and glycogen branching enzymes--all enzymes involved in hydrolysis or synthesis of alpha-1,6-glucosidic linkages in starch and related polysaccharides. This has allowed identification of the transferase active site of the glycogen debranching enzyme and the locations of beta-->alpha loops making up the active sites of all enzymes studied. Activity and specificity of the enzymes are discussed in terms of conserved amino acid residues and loop variations. An evolutionary distance tree of 47 amylolytic and related enzymes is built on 37 residues representing the four best conserved beta-strands of the barrel. It exhibits clusters of enzymes close in specificity, with the branching and glycogen debranching enzymes being the most distantly related.

Partial purification and characterization of soluble acid invertases from rice (Oryza sativa) leaves

There are three soluble acid invertases in the leaves of rice. They could be separated by DEAE1-Sephacel chromatography, and named IT1, IT2 and IT3. The molecular weights of IT1, IT2 and IT3, determined by HPLC gel filtration chromatography, were 220 kD, 59 kD and 67 kD, respectively. Their pI values were 6.2, 5.2 and 4.9, respectively. The pH optima of IT1, IT2 and IT3 were 3.5, 6.0 and 5.5 respectively. All of them could hydrolyze sucrose and raffinose but not maltose, therefore they are all beta-fructofuranosidases. The apparent Km values for sucrose and raffinose of IT3 were 7.0 and 14.5 mM, respectively. Exogenous protein BSA could activate IT3. IT3 was inhibited by metal ions--Pb2+, Zn2+, Cu2+, Hg2+ and Ag+. The sulfhydryl group inhibitor, PCMB, and serine protease inhibitor, PMSF, had no effects on IT3 activity. It might indicate that cysteine and serine did not participate directly the active site catalytic reaction of IT3.

Immobilization and stabilization of invertase using specific polyclonal antibodies

Antisera raised in rabbits to baker's-yeast invertase significantly activated the enzyme in vitro. The antisera contained precipitating antibodies, a significant fraction of which appeared to be directed against the glycosyl residues of the enzyme. Invertase could be immobilized as insoluble enzyme antibody adducts or by binding to a Sepharose matrix precoupled with the gamma-globulin fraction derived from the antisera. The immobilized invertase preparations exhibited high enzyme activity and had markedly enhanced thermal stability, which could be further improved by cross-linking with glutaraldehyde.

Amino acid sequence and thermostability of xylanase A from Schizophyllum commune

The amino acid sequence (197 residues) of xylanase A from the fungus, Schizophyllum commune, was determined by automated analysis of peptides from proteolytic and acid cleavage. The sequence is similar to two Trichoderma xylanases (approximately 56% identical amino acids), but also shows at least 40% identities with xylanases from Bacillus subtilis, B. pumilus and B. circulans. The conserved regions of the enzyme contain only two glutamic acid residues which implicates their possible involvement in catalysis. The disulfide bond in xylanase A is not conserved in this family. In spite of this, the B. subtilis xylanase was found to be more thermostable than xylanase A.

Kinetics of folding and association of differently glycosylated variants of invertase from Saccharomyces cerevisiae

A core-glycosylated form of the dimeric enzyme invertase has been isolated from secretion mutants of Saccharomyces cerevisiae blocked in transport to the Golgi apparatus. This glycosylation variant corresponds to the form that folds and associates during biosynthesis of the protein in vivo. In the present work, its largely homogeneous subunit size and well-defined quaternary structure were utilized to characterize the folding and association pathway of this highly glycosylated protein in comparison with the nonglycosylated cytoplasmic and the high-mannose-glycosylated periplasmic forms of the same enzyme encoded by the suc2 gene. Renaturation of core-glycosylated invertase upon dilution from guanidinium-chloride solutions follows a unibimolecular reaction scheme with consecutive first-order subunit folding and second-order association reactions. The rate constant of the rate-limiting step of subunit folding, as detected by fluorescence increase, is k1 = 1.6 +/- 0.4 x 10(-3) s-1 at 20 degrees C; it is characterized by an activation enthalpy of delta H++ = 65 kJ/mol. The reaction is not catalyzed by peptidyl-prolyl cis-trans isomerase of the cyclophilin type. Reactivation of the enzyme depends on protein concentration and coincides with subunit association, as monitored by size-exclusion high-pressure liquid chromatography. The association rate constant, estimated by numerical simulation of reactivation kinetics, increases from 5 x 10(3) M-1 s-1 to 7 x 10(4) M-1 s-1 between 5 and 30 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of beta-fructofuranosidase from Aspergillus japonicus TIT-KJ1

A beta-fructofuranosidase (EC 3.2.1.26) was purified to homogeneity from Aspergillus japonicus TIT-KJ1. The enzyme had an optimum pH for activity of 5.4 and pH stability at 7.0-8.4. The optimum temperature at pH 5.4 was 60 degrees C. The enzyme had a molecular weight of 236,000 with two subunits and an isoelectric point of pH 4.0. The enzyme was inactivated by 5 mM Hg2+ and Ag+. The enzyme had a high transfructosylating activity. Treatment of 50% (w/v) sucrose with the enzyme under optimum conditions afforded more than 55% fructooligosaccharides.

Purification and characterization of two 1,4-beta-xylan endohydrolases from the rumen fungus Neocallimastix frontalis

Two beta-endoxylanases produced by Neocallimastix frontalis have been purified by ammonium sulfate precipitation, gel filtration, and ion-exchange chromatography. Xylanase I is a nonglycosylated protein with an apparent molecular mass of 45 kDa. Xylanase II is a glycoprotein with an apparent molecular mass of 70 kDa. The pH optima of these enzymes were 5.5 and 6, respectively, and the temperature optimum was 55 degrees C for each enzyme. The endo mode of action of the enzymes was revealed by thin-layer chromatography of xylan hydrolysates. Antibodies raised against each purified protein exhibited no cross-reaction, confirming the biochemical specificities of the enzymes. Both enzymes exhibited carboxymethyl cellulase activity, and xylanase I was absorbed on crystalline cellulose, indicating that these enzymes might belong to the F family of beta-1,4-glycanases.