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T Fukamizo

Publications and source records attributed to T Fukamizo.

At least 37 records · Page 2Linked to original sources
PubMed1995

Site-directed mutagenesis of evolutionary conserved carboxylic amino acids in the chitosanase from Streptomyces sp. N174 reveals two residues essential for catalysis.

The comparison of four sequences of prokaryotic chitosanases, belonging to the family 46 of glycosyl hydrolases, revealed a conserved N-terminal module of 50 residues, including five invariant carboxylic residues. To verify if some of these residues are important for catalytic activity in the chitosanase from Streptomyces sp. N174, these 5 residues were replaced by site-directed mutagenesis. Substitutions of Glu-22 or Asp-40 with sterically conservative (E22Q, D40N) or functionally conservative (E22D, D40E) residues reduced drastically specific activity and kcat, while Km was only slightly changed. The other residues examined, Asp-6, Glu-36, and Asp-37, retained significant activity after mutation. Circular dichroism studies of the mutant chitosanases confirmed that the observed effects are not due to changes in secondary structure. These results suggested that Glu-22 and Asp-40 are directly involved in the catalytic center of the chitosanase and the other residues are not essential for catalytic activity.

Amino Acid Sequence↗
PubMed1995

Reaction mechanism of chitosanase from Streptomyces sp. N174.

Chitosanase was produced by the strain of Streptomyces lividans TK24 bearing the csn gene from Streptomyces sp. N174, and purified by S-Sepharose and Bio-Gel A column chromatography. Partially (25-35%) N-acetylated chitosan was digested by the purified chitosanase, and structures of the products were analysed by NMR spectroscopy. The chitosanase produced heterooligosaccharides consisting of D-GlcN and GlcNAc in addition to glucosamine oligosaccharides [(GlcN)n, n = 1, 2 and 3]. The reducing- and non-reducing-end residues of the heterooligosaccharide products were GlcNAc and GlcN respectively, indicating that the chitosanase can split the GlcNAc-GlcN linkage in addition to that of GlcN-GlcN. Time-dependent 1H-NMR spectra showing hydrolysis of (GlcN)6 by the chitosanase were obtained in order to determine the anomeric form of the reaction products. The chitosanase was found to produce only the alpha-form; therefore it is an inverting enzyme. Separation and quantification of (GlcN)n was achieved by HPLC, and the time course of the reaction catalysed by the chitosanase was studied using (GlcN)n (n = 4, 5 and 6) as the substrate. The chitosanase hydrolysed (GlcN)6 in an endo-splitting manner producing (GlcN)2, (GlcN)3 and (GlcN)4, and did not catalyse transglycosylation. Product distribution was (GlcN)3 >> (GlcN)2 > (GlcN)4. Cleavage to (GlcN)3 + (GlcN)3 predominated over that to (GlcN)2 + (GlcN)4. Time courses showed a decrease in rate of substrate degradation from (GlcN)6 to (GlcN)5 to (GlcN)4. It is most likely that the substrate-binding cleft of the chitosanase can accommodate at least six GlcN residues, and that the cleavage point is located at the midpoint of the binding cleft.

Acetylation↗
PubMed1995

Hen-egg-white lysozyme modified with histamine. State of the imidazolylethyl group covalently attached to the binding site and its effect on the sugar-binding ability.

The chemical modification of Asp101 which is located at the upper end-most site (site A) of the binding cleft of hen egg white lysozyme affects the sugar residue binding of the midmost site (site C) in addition to that of site A, and results in the considerable decrease in the enzymic activity [Fukamizo, T., Hayashi, K. & Goto, S. (1986) Eur. J. Biochem. 158, 463-467]. In the present study, Asp101 was modified with histamine and converted to [2-imidazol-4(5)-ylethyl]asparagine. Contrary to the findings described above, the specific activity of the modified lysozyme was higher than that of the native lysozyme by a factor of about two, and the loss of sugar residue binding ability caused by the modification was found to be restricted to site A. From the H-NMR spectra of the modified lysozyme, the pKa value of the imidazolylethyl group covalently attached to Asp101 was 7.1, and was higher than that of N-acetylhistidinemethylamide (6.65). This indicates that the imidazolylethyl moiety is not exposed to the solvent but adheres to the surface of the lysozyme molecule in an unidentified manner. When N-acetylglucosamine trisaccharide [GlcNAc)3] was added to the modified lysozyme, the 1H-NMR signals of H2 and H4 of the imidazolylethyl group were strongly affected. This indicates that the imidazolylethyl moiety is located near (GlcNAc)3 binding region. When the H gamma signal of Ile98 was saturated, nuclear Overhauser effects were observed on H2 and H4 resonances of the imidazolylethyl moiety. NOE was also observed on the signal of Trp63 H6 upon the saturation of the H4 signal of the imidazolylethyl moiety. Thus, the imidazolylethyl moiety should be located near Trp63 and Ile98, which are in the hydrophobic box most proximal to the sugar binding cleft. This situation of the imidazolylethyl moiety did not result in steric hindrance to the sugar residue binding at sites B and C. The modification affected only the sugar residue binding at site A, and resulted in the enhanced activity.

Acetylglucosamine↗
PubMed1995

Binding mode of N,N',N",N"'-tetraacetylchitotetraitol to hen egg white lysozyme.

The binding of N,N',N",N"'-tetraacetylchitotetraitol [(GlcNAc)4-ol] to hen egg white lysozyme was investigated by fluorescence and 1H NMR spectroscopy. From observation of changes in the fluorescence intensity, the association constants of (GlcNAc)4-ol and (GlcNAc)3 were found to be 0.70 x 10(5) and 1.07 x 10(5) M-1, respectively, at pH 5.0 and 30 degrees C. The lack of a substantial difference between the association constants suggests that the binding mode of the (GlcNAc)3 moiety of (GlcNAc)4-ol is basically similar to that of (GlcNAc)3, but that the N-acetylglucosaminitol residue of (GlcNAC)4-ol does not interact significantly with lysozyme. On the other hand, 1H NMR spectroscopy revealed a minor difference in the binding modes of the two saccharides. For most of the 1H signals responding to saccharide binding, such as those of Trp 63 H2, Trp 28 H5, and Ile 98 H gamma 1, the chemical shift changes induced by (GlcNAc)4-ol were almost identical to those induced by (GlcNAc)3. However, the effect of binding on the signals of Asn 59 H alpha and Trp 108 indole N1H, which are located near subsite C, was different for (GlcNAc)4-ol and (GlcNAc)3. Thus it is inferred that the binding mode of the first sugar residue of (GlcNAc)4-ol to subsite C is somewhat different from that of (GlcNAc)3.

Animals↗
PubMed1994

Specificity of chitosanase from Bacillus pumilus.

Partially (25-35%) N-acetylated chitosan was digested by chitosanase from Bacillus pumilus BN-262, and structures of the products, partially N-acetylated chitooligosaccharides, were analyzed in order to investigate the specificity of the chitosanase. The chitosanase produced glucosamine (GlcN) oligosaccharides abundantly, indicating that the chitosanase splits the beta-1,4-glycosidic linkage of GlcN-GlcN. The chitosanase also produced hetero-oligosaccharides consisting of glucosamine and N-acetyl-D-glucosamine (GlcNAc). Three types of the hetero-oligosaccharides purified by cation-exchange chromatography and HPLC were found to have GlcNAc residue at their reducing end and GlcN residue at their non-reducing end, indicating that the chitosanase can also split the linkage of GlcNAc-GlcN. The determination of the mode of action toward partially N-acetylated chitosan enables a classification of chitosanases according to their specificities and a more precise definition of chitosanases.

Bacillus↗
PubMed1992

1H-NMR study on the chitotrisaccharide binding to hen egg white lysozyme.

Interaction between hen egg white lysozyme and chitotrisaccharide was investigated by 1H-NMR spectroscopy using partially acetylated chitotrisaccharides and chemically modified lysozyme. Monoacetyl (GlcN-GlcN-GlcNAc), diacetyl (GlcN-GlcNAc-GlcNAc), or triacetyl chitotrisaccharide [(GlcNAc)3] was added to the lysozyme solution, and the changes in the 1H-NMR signals of the lysozyme were analyzed. Although many of the resonances were affected by addition of the saccharide, the most remarkable effect was seen on the signal of Trp28 C5H which is in a hydrophobic box adjacent to the saccharide-binding site. The signal shifted upfield by 0.2 ppm upon (GlcNAc)3 binding, whereas the chemical shift change of the signal resulting from binding of GlcN-GlcNAc-GlcNAc or GlcN-GlcN-GlcNAc was smaller than that resulting from (GlcNAc)3 binding. When the Asp101-modified lysozyme was used instead of the native lysozyme, the chemical shift change of the Trp28 C5H signal resulting from (GlcNAc)3 binding was also smaller than that for the native lysozyme. The chemical shift change of the signal reflects the conformational change of the hydrophobic box region which should synchronize with the movement of the binding site resulting from the saccharide binding. Therefore, the conformational change resulting from the saccharide binding might be reduced when the sugar residues located at binding subsites A and B of the lysozyme are deacetylated, as well as when Asp101 interacting with the sugar residues at the same subsites is modified.

Animals↗
PubMed1992

Chitinous components of the cell wall of Fusarium oxysporum.

The cell wall of Fusarium oxysporum f. sp. lycopersici was digested with chitinase to analyze the structure of its chitinous components. In spite of a similar acetylation degree of the cell wall components to that of 25-35% acetylated chitosan, only N-acetylglucosamine disaccharide [(GlcNAc)2] was obtained from chitinase hydrolyzate of the fungal cell wall by CM-Sephadex C-25 column chromatography, while (GlcNAc)2 and several types of deacetylated chitooligosaccharides were separated from that of 25-35% acetylated chitosan. The results indicate that N-acetylglucosamine residues in the polysaccharide chains of the fungal cell wall are most likely condensed into some region, while acetylated residues are more scattered in 25-35% acetylated chitosan.

Carbohydrate Sequence↗
PubMed1991

Lysozyme-catalyzed reaction in continuous flow system.

The lysozyme-catalyzed reaction of chitooligosaccharide was carried out in a continuous flow system in which the solution of substrate, chitooligosaccharide [(GlcNAc)n], flowed into the lysozyme solution in an ultrafiltration apparatus and the products were filtered off. The filtrate was continuously collected in test tubes with the aid of a fraction collector. The product distribution in each fraction was analyzed by high performance gel filtration. Using (GlcNAc)5 as the substrate, the concentrations of products, (GlcNAc)1----4, increased gradually and came to the steady state when the volume of the outflow amounted to sixfold of the inside volume. Before reaching the steady state, the product distribution was quite different from that observed in the closed reaction system, in which the reaction species are not exchangeable through the boundary of the system. The outflows of (GlcNAc)3-5 were delayed in comparison with those of GlcNAc and (GlcNAc)2. The delay period increased with the decrease in substrate concentration, and was shortened by using the [Asp 101 or Trp 62]-modified lysozyme instead of the native lysozyme. These results suggest that the delay in the (GlcNAc)3-5 outflows is caused by the nonproductive binding of the oligosaccharide to the lysozyme molecule. The profile of the flow reaction yields information not only on the catalytic efficiency but also on the substrate binding efficiency of the lysozyme.

Acetylglucosamine↗
PubMed1991

1H-NMR study on the structure of lysozyme from guinea hen egg white.

The structure of lysozyme from guinea hen egg white (GEWL), which differs from hen egg white lysozyme (HEWL) by ten amino acid substitutions, was investigated by nuclear magnetic resonance (NMR) spectroscopy. GEWL and HEWL were very similar to each other in their tertiary structure as judged from the profile of 1H-NMR spectra, pH titration, and an N-acetylglucosamine trisaccharide [(GlcNAc)3 binding experiment. However, we have noticed several characteristics which distinguish GEWL from HEWL. The signal of Trp 108 indole N1H of GEWL was shifted upfield by about 0.3 ppm when compared with that of HEWL, and its hydrogen exchange was faster than that of HEWL. The pKa values of Glu 35 estimated from the pH titration curve of Trp 108 indole N1H were different between GEWL and HEWL. From a careful examination of spectral changes caused by (GlcNAc)3 binding, the changes in the chemical shift values of Trp 28 C5H and Asn 59 alpha CH of GEWL were found to be slightly larger than those of HEWL. Ile 55 of HEWL is replaced by valine in GEWL. Such a replacement may affect the neighboring hydrogen bonding between the main chain C = O of Leu 56 and Trp 108 indole N1H, resulting in a change in the microenvironment of the substrate-binding site near Trp 108.

Acetylglucosamine↗
PubMed1990

State of binding subsites in Asp 101-modified lysozymes.

The environments of the binding subsites in Asp 101-modified lysozyme, in which glucosamine or ethanolamine is covalently bound to the carboxyl group of Asp 101, were investigated by chemical modification and nuclear magnetic resonance spectroscopy. Trp 62 in each of the native and the modified lysozymes was nitrophenylsulfenylated. The yield of the nitrophenylsulfenylated derivative from the lysozyme modified with glucosamine at Asp 101 (GlcN-lysozyme) was considerably lower than those from native lysozyme and from the lysozyme modified with ethanolamine at Asp 101 (EtN-lysozyme). These results suggest that Trp 62 in GlcN-lysozyme is less susceptible to nitrophenylsulfenylation. Kinetic analyses of the [Trp 62 and Asp 101]-doubly modified lysozymes indicated that the nitrophenylsulfenylation of Trp 62 in the native lysozyme, EtN-lysozyme, or GlcN-lysozyme decreased the sugar residue affinity at subsite C while increasing the binding free energy change by 2.7 kcal/mol, 1.5 kcal/mol, or 0.1 kcal/mol, respectively. Although the profile of tryptophan indole NH resonances in the 1H-NMR spectrum for EtN-lysozyme was not different from that for the native lysozyme, the indole NH resonance of Trp 62 in GlcN-lysozyme was apparently perturbed in comparison with that of native lysozyme. These results suggest that the environment of subsite C in GlcN-lysozyme is considerably different from those in native lysozyme and EtN-lysozyme. The glucosamine residue attached to Asp 101 may contact the sugar residue binding site of the lysozyme, affecting the environment of subsite C.

Amino Acid Sequence↗
PubMed1990

Action pattern of Aeromonas hydrophila chitinase on partially N-acetylated chitosan.

Oligosaccharides from the digestion of 34% N-acetylated chitosan by Aeromonas hydrophila chitinase were separated by CM-Sephadex C-25 column chromatography. Sugar compositions and the sequences of main oligosaccharides were identified through their N-acetylation, their cleavage with exo-glycosidases, and their degradation with nitrous acid. Hetero-chitooligosaccharides such as GlcN.GlcNAc, GlcN.GlcNAc.GlcNAc, GlcNAc.GlcN.GlcNAc, and GlcNAc.GlcN.GlcNAc.GlcNAc, together with GlcNAc and (GlcNAc)2, were detected. The structure of GlcN.GlcNAc was confirmed by the analysis with proton and carbon NMR spectroscopy. These studies indicate that Aeromonas hydrophila chitinase is more specific toward the N-acetyl-beta-D-glucosaminidic bonds in partially N-acetylated chitosan.

Acetylation↗
PubMed1987

Retention of anomeric form in lysozyme-catalyzed reaction.

A lysozyme-catalyzed reaction is initiated by a cleavage of the beta-1, 4-glucosaminide linkage, followed by hydration and transglycosylation. Since all glycosides produced by transglycosylation have beta-glycosidic linkages between the sugar and the acceptor moieties, the lysozyme-catalyzed reaction has been classified as an anomer-retention reaction. However, there is no experimental evidence on the anomer retention of the new reducing residue produced by the hydrolysis of the substrate. In the present study, an attempt was made to determine the anomeric form of the GlcNAc residue at the reducing end in nascent hydrolytic products. The anomeric forms of the enzymatic products were separated and quantitatively analyzed by high-performance liquid chromatography. The amounts of alpha- and beta-anomers in the product were plotted against the reaction time. Computer analysis of the experimental data indicated that the nascent hydrolytic product takes only the beta-anomeric form and that the alpha-anomer is formed from beta-anomer by mutarotation.

Acetylglucosamine↗
PubMed1986

Substrate size dependence of lysozyme-catalyzed reaction.

In the study of the mechanism of lysozyme-catalyzed reactions, it has been assumed that the rate constants in the catalytic process, the catalytic activity of catalytic group Glu 35, are independent of the degree of polymerization (size) of the substrate. The characteristics of substrate binding subsite F have recently been reexamined and the substrate binding mode at this subsite has been demonstrated to be more complex than expected from a model based on an X-ray analysis of the lysozyme-substrate complex. In the present study, the time courses of the lysozyme-catalyzed reactions with the substrates chitotetraose [(GlcNAc)4], chitopentaose [(GlcNAc)5], and chitohexaose [(GlcNAc)6], of 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc), were obtained experimentally with high-performance liquid chromatography. From the experimental time courses, the values of the rate constants, k+1 (the cleavage of glycosidic linkage) and k-1/k+2 (relative efficiency of transglycosylation), were obtained by a data-fitting method with computer simulation of the lysozyme-catalyzed reaction (A. Masaki et al. (1981) J. Biochem. 90, 1167-1175). As a result, it was found that the k+1 value is dependent on the substrate size and the value of the binding free energy of subsite F is considerably smaller than previously estimated. The substrate size dependence of the k+1 value is considered to relate closely to the fine structure of the binding and catalytic sites.

Animals↗
PubMed1986

Analysis of chitin structure by nuclear magnetic resonance spectroscopy and chitinolytic enzyme digestion.

Solid-state 13C-NMR analysis of chitin prepared from cuticle of the tobacco hornworm, Manduca sexta (L.), and of crab yielded spectra that demonstrate a high degree of chemical homogeneity (greater than 95%) for the preparations. The chemical shifts of the well-resolved carbon signals from both samples matched closely those of the monomeric unit 2-acetamido-2-deoxy-D-glucopyranoside (GlcNAc). Chromatographic analysis of products from the digestion of chitin by the binary chitinase system (endo splitting chitinase and exo splitting beta-N-acetylglucosaminidase) isolated from M. sexta molting fluid showed that the major product from both chitin preparations is GlcNAc. Also detected was a minor product (product U) that had a chromatographic retention time on the carbohydrate analysis column intermediate between those of chitin penta- and hexasaccharides. Gel filtration chromatography of U indicated that U had an apparent molecular weight intermediate between that of GlcNAc and of N,N'-diacetylchitobiose. Cation-exchange chromatography of U after acid hydrolysis revealed the presence of glucosamine only. Derivatization with trinitrobenzenesulfonate showed the presence of a free amino group in U. Solution proton and carbon NMR spectroscopy were used to identify U as a N-monoacetylchitobiose [O-beta-D-2-amino-2-deoxyglucopyranosyl- (1----4)-2-acetamido-2-deoxy-beta-D-glucopyranose] with the residue at the nonreducing end deacetylated. These studies showed that chitin prepared from alkali- and heat-treated insect or crab cuticle contains trace levels of deacetylated residues that are released as a dead-end product, N-monoacetylchitobiose, after digestion by the binary enzyme system.

Acetylglucosamine↗
PubMed1986

The role of binding subsite A in reactions catalyzed by hen egg-white lysozyme.

The role of binding subsite A, located at the terminal of the six binding subsites of hen egg-white lysozyme, in substrate binding and catalytic reactions was investigated by kinetic studies using a chemical modification method. Computer simulation showed that, although subsite A participates in the binding of the substrate, a decrease in the affinity of subsite A to the sugar residue does not cause a lowering of the rate of substrate consumption but changes the mode of the reaction by changing the distribution of the products formed. The binding free energies of subsites for Asp-101-modified lysozymes were estimated by data-fitting from the experimental time-courses. The contribution of Asp-101 in hen egg-white lysozyme to the substrate binding at subsite A was estimated to correspond to a binding free energy of about -3 kJ/mol, 30% of the total binding free energy of subsite A. Modification of Asp-101 affected not only the binding free energy of subsite A but also that of subsite C.

Animals↗
PubMed1983

Enzymatic activity of avian egg-white lysozymes.

The experimental time-courses of eight avian lysozymes, seven hen-type lysozymes and one goose-type lysozyme, were measured with a substrate of chitopentaose (GlcNAc)5 at pH 5.0 and 50 degrees C. Chitooligosaccharides in the reaction mixture were analyzed by high-performance gel-filtration. From the experimental time-courses, the overall reaction rates represented by the disappearance of the initial substrate and the values of reaction parameters were estimated by computer analysis. With taking hen lysozyme as the reference, the values of reaction parameters estimated were correlated to the replaced amino acid residue in the binding site of the lysozyme, and the roles of some amino acid residues in the binding site were discussed.

Animals↗
PubMed1982

Separation and mutarotation of anomers of chitooligosaccharides.

In the course of a study on the lysozyme-catalyzed reaction of chitooligosaccharides, it was found that each chitooligosaccharide gave two completely separated peaks on high-performance liquid chromatography with a partition column. Synthetic 2-acetamido-2-deoxy-beta-D-glucopyranose gave [alpha] D14 = -18.1 degrees (c = 0.51, H2O) and a large second peak with a minor first peak on high-performance liquid chromatography. When an aqueous solution of the beta-anomer was allowed to stand, the area of the first peak on high-performance liquid chromatography increased, together with a decrease in the area of the second peak and an increase in [alpha] D value. It was concluded that the two peaks of each chitooligosaccharide on high-performance liquid chromatography were due to the separation of alpha- and beta-anomers. The mutarotation of 2-acetamido-2-deoxy-beta-D-glucopyranose was followed by monitoring the [alpha] D value and in the peak area of the two peaks on high-performance liquid chromatography. It was found that the ratios of alpha- and beta-anomers of chitooligosaccharides produced by the lysozyme-catalyzed reaction of chitopentose were different from those of the corresponding authentic chitooligosaccharides which were allowed to stand in the absence of the enzyme under the conditions used for the enzymatic reaction.

Catalysis↗