Purification and properties of Aspergillus niger beta-glucosidase

Characterization of a New Glucose-Tolerant GH1 β-Glycosidase from Aspergillus fumigatus with Transglycosylation Activity

Concern over environmental impacts has spurred many efforts to replace fossil fuels with biofuels such as ethanol. However, for this to be possible, it is necessary to invest in other production technologies, such as second generation (2G) ethanol, in order to raise the levels of this product and meet the growing demand. Currently, this type of production is not yet economically feasible, due to the high costs of the enzyme cocktails used in saccharification stage of lignocellulosic biomass. In order to optimize these cocktails, the search for enzymes with superior activities has been the goal of several research groups. For this end, we have characterized the new β-glycosidase AfBgl1.3 from A. fumigatus after expression and purification in Pichia pastoris X-33. Structural analysis by circular dichroism revealed that increasing temperature destructured the enzyme; the apparent T_m value was 48.5 °C. The percentages of α-helix (36.3%) and β-sheet (12.4%) secondary structures at 25 °C were predicted. Biochemical characterization suggested that the optimal conditions for AfBgl1.3 were pH 6.0 and temperature of 40 °C. At 30 and 40 °C, the enzyme was stable and retained about 90% and 50% of its activity, respectively, after pre-incubation for 24 h. In addition, the enzyme was highly stable at pH between 5 and 8, retaining over 65% of its activity after pre-incubation for 48 h. AfBgl1.3 co-stimulation with 50-250 mM glucose enhanced its specific activity by 1.4-fold and revealed its high tolerance to glucose (IC₅₀ = 2042 mM). The enzyme was active toward the substrates salicin (495.0 ± 49.0 U mg^-1), pNPG (340.5 ± 18.6 U mg^-1), cellobiose (89.3 ± 5.1 U mg^-1), and lactose (45.1 ± 0.5 U mg^-1), so it had broad specificity. The V_max values were 656.0 ± 17.5, 706.5 ± 23.8, and 132.6 ± 7.1 U mg^-1 toward p-nitrophenyl-β-D-glucopyranoside (pNPG), D-(-)-salicin, and cellobiose, respectively. AfBgl1.3 displayed transglycosylation activity, forming cellotriose from cellobiose. The addition of AfBgl1.3 as a supplement at 0.9 FPU/g of cocktail Celluclast^® 1.5L increased carboxymethyl cellulose (CMC) conversion to reducing sugars (g L^-1) by about 26% after 12 h. Moreover, AfBgl1.3 acted synergistically with other Aspergillus fumigatus cellulases already characterized by our research group-CMC and sugarcane delignified bagasse were degraded, releasing more reducing sugars compared to the control. These results are important in the search for new cellulases and in the optimization of enzyme cocktails for saccharification.

Novel β-Glucosidase Mibgl3 from Microbacterium sp. XT11 with Oligoxanthan-Hydrolyzing Activity

The enzymatic pathway of xanthan depolymerization has been predicted previously; however, the β-glucosidase and unsaturated glucuronyl hydrolase in this system have not been cloned and characterized. This lack of knowledge hinders rational modification of xanthan and exploration of new applications. In this work, we report on the properties of Mibgl3, a xanthan-degrading enzyme isolated from Microbacterium sp. XT11. Mibgl3 exhibits typical structural features of the GH3 family but shares low sequence identity with reported GH3 enzymes. The activity of Mibgl3 can be inhibited by Cu²⁺, Fe²⁺, Zn²⁺, and glucose. Unlike most β-glucosidases, Mibgl3 can tolerate a wide pH range and is activated by high concentrations of NaCl. This improves the commercial value of Mibgl3. In particular, Mibgl3 exhibits higher substrate specificity toward oligoxanthan than other β-glucosidases. Ion chromatography, ultrahigh-performance liquid chromatography-mass spectrometry (UPLC-MS), and GC-MS results showed that Mibgl3 could effectively hydrolyze oligoxanthan to release glucose and glucuronate. Therefore, Mibgl3 might play an important role in xanthan depolymerization by functioning as hydrolase of both the xanthan backbone and sidechains. This knowledge of the enzymatic properties and hydrolysis mechanism of a β-glucosidase will be beneficial for future applications.

Biochemical Characterization of Thermostable Carboxymethyl Cellulase and β-Glucosidase from Aspergillus fumigatus JCM 10253

Second-generation biofuel production has emerged as a prominent sustainable and alternative energy. The biochemical properties of cellulolytic enzymes are imperative for cellulosic biomass conversion into fermentable sugars. In the present study, thermostable CMCase and β-glucosidase were purified and characterized from Aspergillus fumigatus JCM 10253. The enzymes were purified through 80% ammonium sulfate precipitation, followed by dialysis and DEAE-cellulose ion-exchange chromatography. The molecular masses of the purified CMCase and β-glucosidase were estimated to be 125 kDa and 90 kDa, respectively. The CMCase and β-glucosidase demonstrated optimum activities at pH 6.0 and 5.0, respectively. Their respective maximum temperatures were 50 and 60 °C. The cellulase activities were stimulated by 10 mM concentration of Ca²⁺, Ni²⁺, Fe²⁺, Mg²⁺, Cu²⁺, Mn²⁺, Zn²⁺, and Pb²⁺ ions. The CMCase activity was enhanced by surfactant Triton X-100 but marginally influenced by most inhibitors. The β-glucosidase retained its activity in the presence of organic solvents (30%) isoamyl alcohol, heptane, toluene, and ethyl acetate, while CMCase was retained with acetone during a prolonged incubation of 168 h. The K_m and V_max values of the two cellulases were studied. The properties of high thermostability and good tolerance against organic solvents could signify its potential use in biofuel production and other value-added products.

Ligand compatibility of salacinol-type α-glucosidase inhibitors toward the GH31 family

We show that salacinol-type α-glucosidase inhibitors are ligand-compatible with the GH 31 family. Salacinol and its 3′-O-benzylated analogs inhibit human lysosomal α-glucosidase at submicromolar levels. Simple structure-activity relationship studies reveal that the salacinol side-chain stereochemistry significantly influences binding to GH31 α-glucosidases.

Salacinol-type α-glucosidase inhibitors are ligand-compatible with the GH 31 family. Salacinol and its 3′-O-benzylated analogs inhibit human lysosomal α-glucosidase at submicromolar levels.

β-Glucosidase BGL1 from Coprinopsis cinerea Exhibits a Distinctive Hydrolysis and Transglycosylation Activity for Application in the Production of 3-O-β-d-Gentiobiosyl-d-laminarioligosaccharides

We previously reported that β-glucosidase BGL1 at low concentration (15 μg mL^-1) from Coprinopsis cinerea exhibited hydrolytic activity only toward laminarioligosaccharides but not toward cellooligosaccharides and gentiobiose. This study shows that BGL1 at high concentration (200 μg mL^-1) also hydrolyzed cellobiose and gentiobiose, which accounted for only 0.83 and 2.05% of its activity toward laminaribiose, respectively. Interestingly, BGL1 at low concentration (1.5 μg mL^-1) showed transglycosylation but BGL1 at high concentration (200 μg mL^-1) did not. BGL1 utilizes only laminarioligosaccharides but not glucose, gentiobiose, and cellobiose to synthesize the higher oligosaccharides. BGL1 transferred one glucosyl residue from substrate laminarioligosaccharide to another laminarioligosaccharide as an acceptor in a β(1 → 3) or β(1 → 6) fashion to produce higher laminarioligosaccharides or 3-O-β-d-gentiobiosyl-d-laminarioligosaccharides. The BGL1-digested laminaritriose exhibited approximately 90% enhancement in the anti-oxidant activity compared to that of untreated laminaritriose, implying a potential application of BGL1-based transglycosylation for the production of high value-added rare oligosaccharides.

A Computational Method to Propose Mutations in Enzymes Based on Structural Signature Variation (SSV)

With the use of genetic engineering, modified and sometimes more efficient enzymes can be created for different purposes, including industrial applications. However, building modified enzymes depends on several in vitro experiments, which may result in the process being expensive and time-consuming. Therefore, computational approaches could reduce costs and accelerate the discovery of new technological products. In this study, we present a method, called structural signature variation (SSV), to propose mutations for improving enzymes’ activity. SSV uses the structural signature variation between target enzymes and template enzymes (obtained from the literature) to determine if randomly suggested mutations may provide some benefit for an enzyme, such as improvement of catalytic activity, half-life, and thermostability, or resistance to inhibition. To evaluate SSV, we carried out a case study that suggested mutations in β-glucosidases: Essential enzymes used in biofuel production that suffer inhibition by their product. We collected 27 mutations described in the literature, and manually classified them as beneficial or not. SSV was able to classify the mutations with values of 0.89 and 0.92 for precision and specificity, respectively. Then, we used SSV to propose mutations for Bgl1B, a low-performance β-glucosidase. We detected 15 mutations that could be beneficial. Three of these mutations (H228C, H228T, and H228V) have been related in the literature to the mechanism of glucose tolerance and stimulation in GH1 β-glucosidase. Hence, SSV was capable of detecting promising mutations, already validated by in vitro experiments, that improved the inhibition resistance of a β-glucosidase and, consequently, its catalytic activity. SSV might be useful for the engineering of enzymes used in biofuel production or other industrial applications.

An ascomycota coculture in batch bioreactor is better than polycultures for cellulase production

Efficient hydrolysis of holocellulose depends on a proper balance between cellulase (endoglucanase, exoglucanase, β-glucosidase) and xylanase activities. The present study aimed to induce the production of cellulases and xylanases using liquid cultures (one, two, three, and four fungal strains on the same bioreactor) of wild strains of Trichoderma harzianum, Aspergillus niger, and Fusarium oxysporum. The strains were identified by amplification and analysis of the ITS rDNA region and the obtained sequences were deposited in Genbank. Enzymes (endoglucanase, exoglucansae, β-glucosidase, and xylanase activities) and the profile of extracellular protein isoforms (SDS-PAGE) produced by different fungal combinations (N = 14) were analyzed by Pearson's correlation matrix and principal component analysis (PCA). According to our results, induction of endoglucanase (19.02%) and β-glucosidase (6.35%) were obtained after 4 days when A. niger and F. oxysporum were cocultured. The combination of A. niger-T. harzianum produced higher endoglucanase in a shorter time than monocultures. On the contrary, when more than two strains were cultured in the same reactor, the relationships of competition were established, trending to diminish the amount of enzymes and the extracellular protein isoforms produced. The xylanase production was sensible to stress produced by mixed cultures, decreasing their activity. This is important when the aim is to produce cellulase-free xylanase. In addition, exoglucanase activity did not change in the combinations tested.

Characterization of two extracellular β-glucosidases produced from the cellulolytic fungus Aspergillus sp. YDJ216 and their potential applications for the hydrolysis of flavone glycosides

A cellulolytic fungus YDJ216 was isolated from a compost and identified as an Aspergillus sp. strain. Two extracellular β-glucosidases, BGL1 and BGL2, were purified using ultrafiltration, ammonium sulfate fractionation, and High-Q chromatography. Molecular masses of BGL1 and BGL2 were estimated to be 97 and 45 kDa, respectively, by SDS-PAGE. The two enzymes eluted as one peak at 87 kDa by Sephacryl S-200 chromatography, and located at similar positions in a zymogram after intact gel electrophoresis, suggesting BGL1 and BGL2 might be monomeric and dimeric, respectively. Both enzymes showed similar enzymatic properties; they were optimally active at pH 4.0-4.5 and 60 °C, and had similar half-lives at 70 °C. Two enzymes also preferred p-nitrophenyl glucose (pNPG) with the same K_m and hardly hydrolyzed cellobiose, suggesting both enzymes are aryl β-glucosidases. However, V_max for pNPG of BGL1 (953.2 U/mg) was much higher than those of BGL2 (66.5U/mg) and other β-glucosidases reported. When tilianin (a flavone glycoside of acacetin) was reacted with both enzymes, inhibitory activity for monoamine oxidase, relating to oxidation of neurotransmitter amines, was increased closely to the degree obtained by acacetin. These results suggest that BGL1 and BGL2 could be used to hydrolyze flavone glycosides to improve their inhibitory activities.

The structural and functional contributions of β-glucosidase-producing microbial communities to cellulose degradation in composting

BACKGROUND

Compost habitats sustain a vast ensemble of microbes that engender the degradation of cellulose, which is an important part of global carbon cycle. β-Glucosidase is the rate-limiting enzyme of degradation of cellulose. Thus, analysis of regulation of β-glucosidase gene expression in composting is beneficial to a better understanding of cellulose degradation mechanism. Genetic diversity and expression of β-glucosidase-producing microbial communities, and relationships of cellulose degradation, metabolic products and the relative enzyme activity during natural composting and inoculated composting were evaluated.

RESULTS

Compared with natural composting, adding inoculation agent effectively improved the degradation of cellulose, and maintained high level of the carboxymethyl cellulose (CMCase) and β-glucosidase activities in thermophilic phase. Gene expression analysis showed that glycoside hydrolase family 1 (GH1) family of β-glucosidase genes contributed more to β-glucosidase activity in the later thermophilic phase in inoculated compost. In the cooling phase of natural compost, glycoside hydrolase family 3 (GH3) family of β-glucosidase genes contributed more to β-glucosidase activity. Intracellular β-glucosidase activity played a crucial role in the regulation of β-glucosidase gene expression, and upregulation or downregulation was also determined by extracellular concentration of glucose. At sufficiently high glucose concentrations, the functional microbial community in compost was altered, which may contribute to maintaining β-glucosidase activity despite the high glucose content.

CONCLUSION

This research provides an ecological functional map of microorganisms involved in carbon metabolism in cattle manure-rice straw composting. The performance of the functional microbial groups in the two composting treatments is different, which is related to the cellulase activity and cellulose degradation, respectively.

Identification and characterization of a novel β-glucosidase via metagenomic analysis of Bursaphelenchus xylophilus and its microbial flora

β-glucosidases catalyze the final step of cellulose hydrolysis and are essential in cellulose degradation. A β-glucosidase gene, cen502, was identified and isolated from a metagenomic library from Bursaphelenchus xylophilus via functional screening. Analyses indicated that cen502 encodes a 465 amino acid polypeptide that contains a catalytic domain belonging to the glycoside hydrolase family 1 (GH1). Cen502 was heterologously expressed, purified, and biochemically characterized. Recombinant Cen502 displayed optimum enzymatic activity at pH 8.0 and 38 °C. The enzyme had highest specific activity to p-nitrophenyl-β-D-glucopyranoside (pNPG; 180.3 U/mg) and had K_m and V_max values of 2.334 mol/ml and 9.017 μmol/min/mg, respectively. The addition of Fe²⁺ and Mn²⁺ significantly increased Cen502 β-glucosidase activity by 60% and 50%, respectively, while 10% and 25% loss of β-glucosidase activity was induced by addition of Pb²⁺ and K⁺, respectively. Cen502 exhibited activity against a broad array of substrates, including cellobiose, lactose, salicin, lichenan, laminarin, and sophorose. However, Cen502 displayed a preference for the hydrolysis of β-1,4 glycosidic bonds rather than β-1,3, β-1,6, or β-1,2 bonds. Our results indicate that Cen502 is a novel β-glucosidase derived from bacteria associated with B. xylophilus and may represent a promising target to enhance the efficiency of cellulose bio-degradation in industrial applications.

Characterization of a glucose-tolerant β-glucosidase from Anoxybacillus sp. DT3-1

BACKGROUND

In general, biofuel production involves biomass pretreatment and enzymatic saccharification, followed by the subsequent sugar conversion to biofuel via fermentation. The crucial step in the production of biofuel from biomass is the enzymatic saccharification. Many of the commercial cellulase enzyme cocktails, such as Spezyme(®) CP (Genencor), Acellerase™ 1000 (Genencor), and Celluclast(®) 1.5L (Novozymes), are ineffectively to release free glucose from the pretreated biomass without additional β-glucosidase.

RESULTS

In this study, for the first time, a β-glucosidase DT-Bgl gene (1359 bp) was identified in the genome of Anoxybacillus sp. DT3-1, and cloned and heterologously expressed in Escherichia coli BL21. Phylogenetic analysis indicated that DT-Bgl belonged to glycosyl hydrolase (GH) family 1. The recombinant DT-Bgl was highly active on cello-oligosaccharides and p-nitrophenyl-β-d-glucopyranoside (pNPG). The DT-Bgl was purified using an Ni-NTA column, with molecular mass of 53 kDa using an SDS-PAGE analysis. It exhibited optimum activity at 70 °C and pH 8.5, and did not require any tested co-factors for activation. The K m and V max values for DT-Bgl were 0.22 mM and 923.7 U/mg, respectively, with pNPG as substrate. The DT-Bgl displayed high glucose tolerance, and retained 93 % activity in the presence of 10 M glucose.

CONCLUSIONS

Anoxybacillus DT-Bgl is a novel thermostable β-glucosidase with low glucose inhibition, and converts long-chain cellodextrins to cellobiose, and further hydrolyse cellobiose to glucose. Results suggest that DT-Bgl could be useful in the development of a bioprocess for the efficient saccharification of lignocellulosic biomass.

Characterization of Aspergillus aculeatus β-glucosidase 1 accelerating cellulose hydrolysis with Trichoderma cellulase system

Aspergillus aculeatus β-glucosidase 1 (AaBGL1), which promotes cellulose hydrolysis by Trichoderma cellulase system, was characterized and compared some properties to a commercially supplied orthologue in A. niger (AnBGL) to elucidate advantages of recombinant AaBGL1 (rAaBGL1) for synergistic effect on Trichoderma enzymes. Steady-state kinetic studies revealed that rAaBGL1 showed high catalytic efficiency towards β-linked glucooligosaccharides. Up to a degree of polymerization (DP) 3, rAaBGL1 prefered to hydrolyze β-1,3 linked glucooligosaccharides, but longer than DP 3, preferred β-1,4 glucooligosaccharides (up to DP 5). This result suggested that there were different formation for subsites in the catalytic cleft of AaBGL1 between β-1,3 and β-1,4 glucooligosaccharides, therefore rAaBGL1 preferred short chain of laminarioligosaccharides and long chain of cellooligosaccharides on hydrolysis. rAaBGL1 was more insensitive to glucose inhibition and more efficient to hydrolyze the one of major transglycosylation product, gentiobiose than AnBGL, resulting that rAaBGL1 completely hydrolyzed 5% cellobiose to glucose faster than AnBGL. These data indicate that AaBGL1 is valuable for the use of cellulosic biomass conversion.

A mechanism of glucose tolerance and stimulation of GH1 β-glucosidases

β-Glucosidases are enzymes that hydrolyze β-glycosidic bonds to release non-reducing terminal glucosyl residues from glycosides and oligosaccharides, and thus have significant application potential in industries. However, most β-glucosidases are feedback inhibited by the glucose product, which restricts their application. Remarkably, some β-glucosidases of the glycoside hydrolase (GH) 1 family are tolerant to or even stimulated by glucose. Elucidation of the mechanisms of glucose tolerance and stimulation of the GH1 β-glucosidases will be crucial to improve their application through enzyme engineering. In this study, by comparing the primary and tertiary structures of two GH1 β-glucosidases with distinct glucose dependence, some putative glucose-dependence relevant sites were mutated to investigate their exact roles. Both biochemical and structural characterization of the mutants suggested that some sites at the entrance and middle of the substrate channel regulate the effects of glucose, and the relative binding affinity/preference of these sites to glucose modulates the glucose dependence. A mechanism was therefore proposed to interpret the glucose dependence of GH1 β-glucosidases. This research provides fresh insight into our current understanding of the properties and mechanisms of GH1 β-glycosidases and related enzymes that modulate their activity via feedback control mechanism.

Glucose-tolerant β-glucosidase retrieved from a Kusaya gravy metagenome

β-glucosidases (BGLs) hydrolyze cello-oligosaccharides to glucose and play a crucial role in the enzymatic saccharification of cellulosic biomass. Despite their significance for the production of glucose, most identified BGLs are commonly inhibited by low (∼mM) concentrations of glucose. Therefore, BGLs that are insensitive to glucose inhibition have great biotechnological merit. We applied a metagenomic approach to screen for such rare glucose-tolerant BGLs. A metagenomic library was created in Escherichia coli (∼10,000 colonies) and grown on LB agar plates containing 5-bromo-4-chloro-3-indolyl-β-D-glucoside, yielding 828 positive (blue) colonies. These were then arrayed in 96-well plates, grown in LB, and secondarily screened for activity in the presence of 10% (w/v) glucose. Seven glucose-tolerant clones were identified, each of which contained a single bgl gene. The genes were classified into two groups, differing by two nucleotides. The deduced amino acid sequences of these genes were identical (452 aa) and found to belong to the glycosyl hydrolase family 1. The recombinant protein (Ks5A7) was overproduced in E. coli as a C-terminal 6 × His-tagged protein and purified to apparent homogeneity. The molecular mass of the purified Ks5A7 was determined to be 54 kDa by SDS-PAGE, and 160 kDa by gel filtration analysis. The enzyme was optimally active at 45°C and pH 5.0-6.5 and retained full or 1.5-2-fold enhanced activity in the presence of 0.1-0.5 M glucose. It had a low KM (78 μM with p-nitrophenyl β-D-glucoside; 0.36 mM with cellobiose) and high V max (91 μmol min(-1) mg(-1) with p-nitrophenyl β-D-glucoside; 155 μmol min(-1) mg(-1) with cellobiose) among known glucose-tolerant BGLs and was free from substrate (0.1 M cellobiose) inhibition. The efficient use of Ks5A7 in conjunction with Trichoderma reesei cellulases in enzymatic saccharification of alkaline-treated rice straw was demonstrated by increased production of glucose.

Characterization of β -Glucosidase Produced by Aspergillus niger under Solid-State Fermentation and Partially Purified Using MANAE-Agarose

β-Glucosidase (BGL) is a hydrolytic enzyme with specificity for a wide variety of glycoside substrates, being an enzyme with a large range of biotechnological applications. However, enzyme properties can be different depending both on the microorganism and the cultivation procedure employed. Therefore, in order to explore potential biocatalytical applications of novel enzymes, their characterization is essential. In this work, a BGL synthesized by a selected strain of Aspergillus niger cultivated under solid-state fermentation (SSF) was partially purified and fully characterized in terms of optimum pH, temperature, and thermostability. The single-step purification using MANAE-agarose in a chromatographic column yielded an enzyme solution with specific activity (17.1 IU/mg protein) adequate for the characterization procedures. Electrophoresis SDS-PAGE and size-exclusion chromatography analysis resulted in an estimated molecular mass of 60 kDa. Higher enzyme activities were found in the range between 40 and 65°C and between pH 4 and 5.5, indicating an interesting characteristic for application in the hydrolysis of lignocellulosic biomass for biofuels production. Thermostability studies of purified BGL resulted in half-lives at 37°C of 56.3 h and at 50°C of 5.4 h. These results provide support for further studies of this enzyme towards revealing its potential biotechnological applications.

A dynamic model for cellulosic biomass hydrolysis: a comprehensive analysis and validation of hydrolysis and product inhibition mechanisms

The objective of this study is to perform a comprehensive enzyme kinetics analysis in view of validating and consolidating a semimechanistic kinetic model consisting of homogeneous and heterogeneous reactions for enzymatic hydrolysis of lignocellulosic biomass proposed by the U.S. National Renewable Energy Laboratory (Kadam et al., Biotechnol Prog 20(3):698-705, 2004) and its variations proposed in this work. A number of dedicated experiments were carried out under a range of initial conditions (Avicel® versus pretreated barley straw as substrate, different enzyme loadings and different product inhibitors such as glucose, cellobiose and xylose) to test the hydrolysis and product inhibition mechanisms of the model. A nonlinear least squares method was used to identify the model and estimate kinetic parameters based on the experimental data. The suitable mathematical model for industrial application was selected among the proposed models based on statistical information (weighted sum of square errors). The analysis showed that transglycosylation plays a key role at high glucose levels. It also showed that the values of parameters depend on the selected experimental data used for parameter estimation. Therefore, the parameter values are not universal and should be used with caution. The model proposed by Kadam et al. (Biotechnol Prog 20(3):698-705, 2004) failed to predict the hydrolysis phenomena at high glucose levels, but when combined with transglycosylation reaction(s), the prediction of cellulose hydrolysis behaviour over a broad range of substrate concentrations (50-150 g/L) and enzyme loadings (15.8-31.6 and 1-5.9 mg protein/g cellulose for Celluclast and Novozyme 188, respectively) was possible. This is the first study introducing transglycosylation into the semimechanistic model. As long as these type of models are used within the boundary of their validity (substrate type, enzyme source and substrate concentration), they can support process design and technology improvement efforts at pilot and full-scale studies.

Highly glucose tolerant β-glucosidase from Aspergillus unguis: NII 08123 for enhanced hydrolysis of biomass

Aspergillus unguis NII-08123, a filamentous fungus isolated from soil, was found to produce β-glucosidase (BGL) activity with high glucose tolerance. Cultivation of the fungus in different carbon sources resulted in the secretion of different isoforms of the enzyme. A low molecular weight isoform, which retained ~60 % activity in the presence of 1.5 M glucose, was purified to homogeneity and the purified enzyme exhibited a temperature and pH optima of 60 °C and 6, respectively. The K  m and V  max of the enzyme were 4.85 mM and 2.95 U/mg, respectively, for 4-nitrophenyl β-d-glucopyranoside. The glucose inhibition constant of the enzyme was 0.8 M, indicating high glucose tolerance, and this is the second-highest glucose tolerance ever reported from the Aspergillus nidulans group. The glucose-tolerant BGL from A. unguis, when supplemented to cellulase preparation from Penicillium, could improve biomass hydrolysis efficiency by 20 % in 12 h compared to the enzyme without additional beta glucosidase supplementation. The beta glucosidase from A. unguis is proposed as a highly potent “blend-in” for biomass saccharifying enzyme preparations.

Cloning, molecular characterization, and mRNA expression of the thermostable family 3 β-glucosidase from the rare fungus Stachybotrys microspora

The filamentous fungus Stachybotrys microspora possess a rich β-glucosidase system composed of five β-glucosidases. Three of them were already purified to homogeneity and characterized. In order to isolate the β-glucosidase genes from S. microspora and study their regulation, a PCR strategy using consensus primers was used as a first step. This approach enabled the isolation of three different fragments of family 3 β-glucosidase gene. A representative genomic library was constructed and probed with one amplified fragment gene belonging to family 3 of β-glucosidase. After two rounds of hybridization, seven clones were obtained and the analysis of DNA plasmids leads to the isolation of one clone (CF3) with the largest insert of 7 kb. The regulatory region shows multiple TC-rich elements characteristic of constitutive promoter, explaining the expression of this gene under glucose condition, as shown by zymogram and RT-PCR analysis. The tertiary structure of the deduced amino acid sequence of Smbgl3 was predicted and has shown three conserved domains: an (α/β)8 triose phosphate isomerase (TIM) barrel, (α/β)5 sandwich, and fibronectin type III domain involved in protein thermostability. Zymogram analysis highlighted such thermostable character of this novel β-glucosidase.

Bioenergy grass feedstock: current options and prospects for trait improvement using emerging genetic, genomic, and systems biology toolkits

For lignocellulosic bioenergy to become a viable alternative to traditional energy production methods, rapid increases in conversion efficiency and biomass yield must be achieved. Increased productivity in bioenergy production can be achieved through concomitant gains in processing efficiency as well as genetic improvement of feedstock that have the potential for bioenergy production at an industrial scale. The purpose of this review is to explore the genetic and genomic resource landscape for the improvement of a specific bioenergy feedstock group, the C4 bioenergy grasses. First, bioenergy grass feedstock traits relevant to biochemical conversion are examined. Then we outline genetic resources available bioenergy grasses for mapping bioenergy traits to DNA markers and genes. This is followed by a discussion of genomic tools and how they can be applied to understanding bioenergy grass feedstock trait genetic mechanisms leading to further improvement opportunities.

Purification and characterization of a ginsenoside Rb(1)-hydrolyzing β-glucosidase from Aspergillus niger KCCM 11239

Rb(1)-hydrolyzing β-glucosidase from Aspergillus niger KCCM 11239 was studied to develop a bioconversion process for minor ginsenosides. The specific activity of the purified enzyme was 46.5 times greater than that of the crude enzyme. The molecular weight of the native enzyme was estimated to be approximately 123 kDa. The optimal pH of the purified enzyme was pH 4.0, and the enzyme proved highly stable over a pH range of 5.0-10.0. The optimal temperature was 70 °C, and the enzyme became unstable at temperatures above 60 °C. The enzyme was inhibited by Cu(2+), Mg(2+), Co(2+), and acetic acid (10 mM). In the specificity tests, the enzyme was found to be active against ginsenoside Rb(1), but showed very low levels of activity against Rb(2), Rc, Rd, Re, and Rg(1). The enzyme hydrolyzed the 20-C,β-(1→6)-glucoside of ginsenoside Rb(1) to generate ginsenoside Rd and Rg(3), and hydrolyzed 3-C,β-(1→2)-glucoside to generate F(2). The properties of the enzyme indicate that it could be a useful tool in biotransformation applications in the ginseng industry, as well as in the development of novel drug compounds.

Mapping the polysaccharide degradation potential of Aspergillus niger

Background

The degradation of plant materials by enzymes is an industry of increasing importance. For sustainable production of second generation biofuels and other products of industrial biotechnology, efficient degradation of non-edible plant polysaccharides such as hemicellulose is required. For each type of hemicellulose, a complex mixture of enzymes is required for complete conversion to fermentable monosaccharides. In plant-biomass degrading fungi, these enzymes are regulated and released by complex regulatory structures. In this study, we present a methodology for evaluating the potential of a given fungus for polysaccharide degradation.

Results

Through the compilation of information from 203 articles, we have systematized knowledge on the structure and degradation of 16 major types of plant polysaccharides to form a graphical overview. As a case example, we have combined this with a list of 188 genes coding for carbohydrate-active enzymes from Aspergillus niger, thus forming an analysis framework, which can be queried. Combination of this information network with gene expression analysis on mono- and polysaccharide substrates has allowed elucidation of concerted gene expression from this organism. One such example is the identification of a full set of extracellular polysaccharide-acting genes for the degradation of oat spelt xylan.

Conclusions

The mapping of plant polysaccharide structures along with the corresponding enzymatic activities is a powerful framework for expression analysis of carbohydrate-active enzymes. Applying this network-based approach, we provide the first genome-scale characterization of all genes coding for carbohydrate-active enzymes identified in A. niger.

Characterization of a thermostable β-glucosidase from Aspergillus fumigatus Z5, and its functional expression in Pichia pastoris X33

BACKGROUND

Recently, the increased demand of energy has strongly stimulated the research on the conversion of lignocellulosic biomass into reducing sugars for the subsequent production, and β-glucosidases have been the focus because of their important roles in a variety fundamental biological processes and the synthesis of useful β-glucosides. Although the β-glucosidases of different sources have been investigated, the amount of β-glucosidases are insufficient for effective conversion of cellulose. The goal of this work was to search for new resources of β-glucosidases, which was thermostable and with high catalytic efficiency.

RESULTS

In this study, a thermostable native β-glucosidase (nBgl3), which is secreted by the lignocellulose-decomposing fungus Aspergillus fumigatus Z5, was purified to electrophoretic homogeneity. Internal sequences of nBgl3 were obtained by LC-MS/MS, and its encoding gene, bgl3, was cloned based on the peptide sequences obtained from the LC-MS/MS results. bgl3 contains an open reading frame (ORF) of 2622 bp and encodes a protein with a predicted molecular weight of 91.47 kDa; amino acid sequence analysis of the deduced protein indicated that nBgl3 is a member of the glycoside hydrolase family 3. A recombinant β-glucosidase (rBgl3) was obtained by the functional expression of bgl3 in Pichia pastoris X33. Several biochemical properties of purified nBgl3 and rBgl3 were determined - both enzymes showed optimal activity at pH 6.0 and 60°C, and they were stable for a pH range of 4-7 and a temperature range of 50 to 70°C. Of the substrates tested, nBgl3 and rBgl3 displayed the highest activity toward 4-Nitrophenyl-β-D-glucopyranoside (pNPG), with specific activities of 103.5 ± 7.1 and 101.7 ± 5.2 U mg-1, respectively. However, these enzymes were inactive toward carboxymethyl cellulose, lactose and xylan.

CONCLUSIONS

An native β-glucosidase nBgl3 was purified to electrophoretic homogeneity from the crude extract of A. fumigatus Z5. The gene bgl3 was cloned based on the internal sequences of nBgl3 obtained from the LC-MS/MS results, and the gene bgl3 was expressed in Pichia pastoris X33. The results of various biochemical properties of two enzymes including specific activity, pH stability, thermostability, and kinetic properties (Km and Vmax) indicated that they had no significant differences.

Characterization of two acidic β-glucosidases and ethanol fermentation in the brown rot fungus Fomitopsis palustris

Two acidic β-glucosidases (βGI and βGII) from the brown rot fungus Fomitopsis palustris were purified to homogeneity by several chromatographic steps. βGI and βGII had molecular weights of 130 and 213 kDa, respectively, and exhibited optimum activity at pH 2.5 and 55°C. The K(m) values of βGI and βGII for p-nitrophenyl-β-d-glucopyranoside were 0.706 and 0.971 mM, respectively. Although the effect of metal ions and inhibitors differed between the two enzymes, both β-glucosidases exhibited preferential glucose release during hydrolysis of cello-oligosaccharides, indicating that βGI and βGII possess effective exo-type activities. Notably, F. palustris was able to produce ethanol when cultured on medium containing 20 g/l of glucose, mannose, cellobiose, and maltose, in which the maximum ethanol concentrations measured were 9.2, 8.7, 9.0, and 8.9 g/l, corresponding to 90.2%, 85.3%, 88.2%, and 87.3% of the theoretical yield, respectively. These findings suggest that F. palustris has the ability not only to secrete β-glucosidase enzymes effective at low pH, but also to function as a biocatalyst, which may be suitable for the conversion of lignocellulosic materials into ethanol.

Beta-1,3-glucanase from Delftia tsuruhatensis strain MV01 and its potential application in vinification

During vinification microbial activities can spoil wine quality. As the wine-related lactic acid bacterium Pediococcus parvulus is able to produce slimes consisting of a β-1,3-glucan, must and wine filtration can be difficult or impossible. In addition, the metabolic activities of several wild-type yeasts can also negatively affect wine quality. Therefore, there is a need for measures to degrade the exopolysaccharide from Pediococcus parvulus and to inhibit the growth of certain yeasts. We examined an extracellular β-1,3-glucanase from Delftia tsuruhatensis strain MV01 with regard to its ability to hydrolyze both polymers, the β-1,3-glucan from Pediococcus and that from yeast cell walls. The 29-kDa glycolytic enzyme was purified to homogeneity. It exhibited an optimal activity at 50°C and pH 4.0. The sequencing of the N terminus revealed significant similarities to β-1,3-glucanases from different bacteria. In addition, the investigations indicated that this hydrolytic enzyme is still active under wine-relevant parameters such as elevated ethanol, sulfite, and phenol concentrations as well as at low pH values. Therefore, the characterized enzyme seems to be a useful tool to prevent slime production and undesirable yeast growth during vinification.

Production, Purification, and Properties of a Thermostable beta-Glucosidase from a Color Variant Strain of Aureobasidium pullulans

A color variant strain of Aureobasidium pullulans (NRRL Y-12974) produced beta-glucosidase activity when grown in liquid culture on a variety of carbon sources, such as cellobiose, xylose, arabinose, lactose, sucrose, maltose, glucose, xylitol, xylan, cellulose, starch, and pullulan. An extracellular beta-glucosidase was purified 129-fold to homogeneity from the cell-free culture broth of the organism grown on corn bran. The purification protocol included ammonium sulfate treatment, CM Bio-Gel A agarose column chromatography, and gel filtrations on Bio-Gel A-0.5m and Sephacryl S-200. The beta-glucosidase was a glycoprotein with native molecular weight of 340,000 and was composed of two subunits with molecular weights of about 165,000. The enzyme displayed optimal activity at 75 degrees C and pH 4.5 and had a specific activity of 315 mumol . min . mg of protein under these conditions. The purified beta-glucosidase was active against p-nitrophenyl-beta-d-glucoside, cellobiose, cellotriose, cellotetraose, cellopentaose, cellohexaose, and celloheptaose, with K(m) values of 1.17, 1.00, 0.34, 0.36, 0.64, 0.68, and 1.65 mM, respectively. The enzyme activity was competitively inhibited by glucose (K(i) = 5.65 mM), while fructose, arabinose, galactose, mannose, and xylose (each at 56 mM) and sucrose and lactose (each at 29 mM) were not inhibitory. The enzyme did not require a metal ion for activity, and its activity was not affected by p-chloromercuribenzoate (0.2 mM), EDTA (10 mM), or dithiothreitol (10 mM). Ethanol (7.5%, vol/vol) stimulated the initial enzyme activity by 15%. Glucose production was enhanced by 7.9% when microcrystalline cellulose (2%, wt/vol) was treated for 48 h with a commercial cellulase preparation (5 U/ml) that was supplemented with the purified beta-glucosidase (0.21 U/ml) from A. pullulans.

Purification and biochemical characterization of a specific beta-glucosidase from the digestive fluid of larvae of the palm weevil, Rhynchophorus palmarum

A beta-glucosidase was purified from the digestive fluid of the palm weevil Rhynchophorus palmarum L. (Coleoptera: Curculionidae) by chromatography on anion-exchange, gel filtration, and hydrophobic interaction columns. The preparation was shown to be homogeneous on polyacrylamide gels, beta-glucosidase is a monomeric protein with a molecular weight of 58 kDa based on its mobility in SDS-PAGE and 60 kDa based on gel filtration. Maximal beta-glucosidase activity occurred at 55 degrees C and pH 5.0. The purified beta-glucosidase was stable at 37 degrees C and its pH stability was in the range of 5.0-6.0. The enzyme readily hydrolyzed p-nitrophenyl-beta-D-glucoside, cellobiose, cellodextrins and required strictly beta-gluco configuration for activity. It cleaved glucose-glucose beta-(1-4) linkages better than beta-(1-2), beta-(1-3) and beta-(1-6) linkages. The catalytic efficiency (K(cat)/K(M)) values for p-nitrophenyl-beta-D-glucoside and cellobiose were respectively 240.48 mM(-1)s(-1) and 134.80 mM(-1)s(-1). Beta-glucosidase was capable of catalysing transglucosylation reactions. The yield of glucosylation of 2-phenylethanol (20 %), catalysed by the beta-glucosidase in the presence of cellobiose as glucosyl donor, is lower than those reported previously with conventional sources of beta-glucosidases. In addition, the optimum pH is different for the hydrolysis (pH 5.0) and transglucosylation reactions (pH 6.6).

Production of ascorbic acid glucoside by alginate-entrapped mycelia of Aspergillus niger

The mycelia of Aspergillus niger, cultivated in a medium containing 45 g l(-1) maltose, 66 g l(-1) yeast extract, and 5 g l(-1) K(2)HPO(4) at 30 degrees C and 200 rpm, were used as a biocatalyst in the glucosylation of ascorbic acid. Free mycelia from 3-day-old culture, when used in a 6-h reaction with maltose as the acyl donor, gave 16.07 g l(-1) ascorbic acid glucoside corresponding to a volumetric productivity of 2.68 g l(-1) h(-1) and a conversion of 67%. Mycelia from 3-day-old cultures were entrapped in calcium alginate beads and used as a catalyst in the glucosylation of ascorbic acid. An ascorbic acid-to-maltose molar ratio of 1:9 was found to be optimum, and the conversion reached 75% after 12 h. The concentration of ascorbic acid glucoside produced at this molar ratio was 17.95 g l(-1), and the productivity was 1.5 g l(-1) h(-1). The biocatalyst was repeatedly used in a fixed bed bioreactor for the synthesis of ascorbic acid glucoside and approximately 17 g l(-1) of ascorbic acid glucoside corresponding to a volumetric productivity of 1.42 g l(-1) h(-1) was produced in each use. The conversion was retained at 70% in each use. The entrapped mycelia also exhibited exceptionally high reusability and storage stability. The product was purified to 85% by anion exchange and gel permeation chromatography with a final yield of 75%.

Transglucosidic reactions of the Aspergillus niger Family 3 β-glucosidase: Qualitative and quantitative analyses and evidence that the transglucosidic rate is independent of pH

The hydrolytic and transglucosidic reactions of the Aspergillus niger Family 3 beta-glucosidase were characterized. Michaelis-Menten plots of the rates of aglycone formation were normal (hyperbolic) at low [substrate]. However, at high [substrate] the rates decreased at pH below approximately 5.5 but increased at pH above approximately 5.5. Each decrease or increase took the form of a second hyperbola adjoining the first. Thin layer chromatography, gas-liquid chromatography, and NMR analyses indicated that the substrates became transglucosidic acceptors when present at high concentrations. When pNPGlc and cellobiose reacted as acceptors, the C6 hydroxyl of the non-reducing substrate component reacted to form beta-D-glucopyranosyl-(1-6)-beta-D-glucopyranosyl-p-nitrophenol and beta-D-glucopyranosyl-(1-6)-beta-D-glucopyranosyl-(1-4)-D-glucopyranose, respectively. The acceptor action accounted for the second adjoining hyperbolas. Rate equations were derived for the production of the aglycone and the transglucosidic intermediate, and these equations described the data very well. Hydrolytic Vmax {Vmax(h)}, hydrolytic Km {Km(h)}, transglucosidic Vmax {Vmax(t)}, and transglucosidic Km {Km(t)} values were obtained by non-linear regression analysis using these equations. Vmax(h) pH profiles were bell shaped with optima between pH 4 and 4.5 but the Vmax(t) values did not change substantially between pH 3 and 7. These differences in the pH profiles explain the decreasing and increasing adjoining hyperbolas since Vmax(t) is lower than Vmax(h) at pH less than approximately 5.5 but higher than Vmax(h) at pH greater than approximately 5.5. The reason for these pH effects is that the value of the hydrolytic rate constant (k3) decreases while the value of the transglucosidic rate constant (k4) does not change between pH 3 and 7. The study also showed that gentiobiose forms by an intermolecular reaction of the C6 hydroxyl of Glc rather than an intramolecular reaction and that an equatorial orientation of the C2 hydroxyl, the presence of a C6 primary hydroxyl and beta-linkages with oligosaccharide acceptors are important for acceptor reactivity.

Purification and characterization of an extracellular β-glucosidase with high transglucosylation activity and stability from Aspergillus niger No. 5.1

An extracellular beta-glucosidase was extracted from the culture filtrate of Aspergillus niger No. 5.1 and purified to homogeneity by using ammonium sulfate precipitation, Chitopearl-DEAE chromatography, and Sephadex G-100 chromatography. The specific activity of the enzyme was enriched 6.33-fold, with a recovery of 11.67%. The enzyme was a monomer and the molecular mass was 67.5 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and 66.5 kDa by gel-filtration chromatography. The enzyme had optimum activity at pH 6.0 and 60 degrees C and was stable over the pH range of 3.0-9.0. It showed specificity of hydrolysis for p-nitrophenyl-beta-D-glucoside and cellobiose. The Km and Vmax values of the enzyme for cellobiose and salicin were 5.34 mM, 2.57 micromol/(mL.s), and 3.09 mM, 1.34 micromol/(mL.s), respectively. Both amino acid composition and N-terminal amino acid sequence of the enzyme were determined, which provides useful information for cloning of this enzyme.

Kinetics of substrate transglycosylation by glycoside hydrolase family 3 glucan (1→3)-β-glucosidase from the white-rot fungus Phanerochaete chrysosporium

To elucidate the interaction between substrate inhibition and substrate transglycosylation of retaining glycoside hydrolases (GHs), a steady-state kinetic study was performed for the GH family 3 glucan (1-->3)-beta-glucosidase from the white-rot fungus Phanerochaete chrysosporium, using laminarioligosaccharides as substrates. When laminaribiose was incubated with the enzyme, a transglycosylation product was detected by thin-layer chromatography. The product was purified by size-exclusion chromatography, and was identified as a 6-O-glucosyl-laminaribiose (beta-D-Glcp-(1-->6)-beta-D-Glcp-(1-->3)-D-Glc) by 1H NMR spectroscopy and electrospray ionization mass spectrometry analysis. In steady-state kinetic studies, an apparent decrease of laminaribiose hydrolysis was observed at high concentrations of the substrate, and the plots of glucose production versus substrate concentration were thus fitted to a modified Michaelis-Menten equation including hydrolytic and transglycosylation parameters (K(m), K(m2), k(cat), k(cat2)). The rate of 6-O-glucosyl-laminaribiose production estimated by high-performance anion-exchange chromatography coincided with the theoretical rate calculated using these parameters, clearly indicating that substrate inhibition of this enzyme is fully explained by substrate transglycosylation. Moreover, when K(m), k(cat), and affinity for glucosyl-enzyme intermediates (K(m2)) were estimated for laminarioligosaccharides (DP=3-5), the K(m) value of laminaribiose was approximately 5-9 times higher than those of the other oligosaccharides (DP=3-5), whereas the K(m2) values were independent of the DP of the substrates. The kinetics of transglycosylation by the enzyme could be well interpreted in terms of the subsite affinities estimated from the hydrolytic parameters (K(m) and k(cat)), and a possible mechanism of transglycosylation is proposed.

Beta-glycosylamidine as a ligand for affinity chromatography tailored to the glycon substrate specificity of beta-glycosidases

An affinity adsorbent for beta-glycosidases has been prepared by using beta-glycosylamidine as a ligand. beta-Glucosylamidine and beta-galactosylamidine, highly potent and selective inhibitors of beta-glucosidases and beta-galactosidases, respectively, were immobilized by a novel one-pot procedure involving the addition of a beta-glycosylamine and 2-iminothiolane.HCl simultaneously to a matrix modified with maleimido groups via an appropriate spacer to give an affinity adsorbent for beta-glucosidases and beta-galactosidases, respectively. This one-pot procedure enables various beta-glycosylamidine ligands to be formed and immobilized conveniently according to the glycon substrate specificities of the enzymes. A crude enzyme extract from tea leaves (Camellia sinensis) and a beta-galactosidase from Penicillium multicolor were chromatographed directly on each affinity adsorbent to give a beta-glucosidase and a beta-galactosidase to apparent homogeneity in one step by eluting the column with glucose or by a gradient NaCl elution, respectively. The beta-glucosidase and beta-galactosidase were inhibited competitively by a soluble form of the corresponding beta-glycosylamidine ligand with an inhibition constant (K(i)) of 2.1 and 0.80 microM, respectively. Neither enzyme was bound to the adsorbent with a mismatched ligand, indicating that the binding of the glycosidases was of specific nature that corresponds to the glycon substrate specificity of the enzymes. The ease of preparation and the selective nature of the affinity adsorbent should promise a large-scale preparation of the affinity adsorbent for the purification and removal of specific glycosidases according to their glycon substrate specificities.

Microbial cellulose utilization: fundamentals and biotechnology

Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

A direct continuous spectrophotometric assay for glycosidases with 3-nitro-2-pyridyl glycosides by tautomerization of 2-hydroxy-3-nitropyridine

Two kinds of 3-nitro-2-pyridyl glycosides were synthesized and evaluated as substrates for continuous spectrophotometric assay for glycosidases. The liberated aglycon, 2-hydroxy-3-nitropyridine, immediately tautomerized to 3-nitro-2(1H)-pyridone, causing an absorption shift of ca. 60 nm even under acidic conditions (pH 3-6). Consequently, the enzymatic hydrolysis of these glycosides was monitored continuously in the acidic to neutral pH range (pH 4-7), the optimum pH for most glycosidases. The absorbance of liberated aglycon increased linearly at 390 nm until 10% consumption of the substrate to enable the initial rate to be determined at once without terminating the reaction. The kinetic parameters for the hydrolysis of 3-nitro-2-pyridyl glycosides were obtained from the slopes of the progress curves and were compared with those obtained from the conventional discontinuous assay using p- and o-nitrophenyl glycosides as substrates. The kinetic parameters indicated that 3-nitro-2-pyridyl glycosides were more activated and specific substrates, but with less affinity to the enzymes than the corresponding nitrophenyl glycosides. Moreover, the absorbance shift by tautomerization should promise further applications to continuous spectrophotometric assays for other enzymes acting under acidic conditions, such as acid proteases and acid phosphatases.