Significant enhancement in the binding of p-nitrophenyl-beta-D-xylobioside by the E128H mutant F/10 xylanase from Streptomyces olivaceoviridis E-86.

Mutagenesis studies were carried out to examine the effects of replacement of either the nucleophile Glu-236 or the acid/base Glu-128 residue of the F/10 xylanase by a His residue. To our surprise, the affinity for the p-nitrophenyl-beta-D-xylobioside substrate was increased by 10(3)-fold in the case of the mutant E128H enzyme compared with that of the wild-type F/10 xylanase. The catalytic activity of the mutant enzymes was low, despite the fact that the distance between the nucleophilic atom (an oxygen in the native xylanase and a nitrogen in the mutant) and the alpha-carbon was barely changed. Thus, the alteration of the acid/base functionality (Glu-128 to His mutation) provided a significantly favorable interaction within the E128H enzyme/substrate complex in the ground state, accompanying a reduction in the stabilization effect in the transition state.

Substrate specificity of alpha-glucuronidase isolated from snail acetone powder.

The substrate specificity of a p-nitrophenyl alpha-D-glucopyranosyl-uronic acid-hydrolyzing enzyme (PNP-GAase) isolated from snail acetone powder has been investigated with various substrates, such as p-nitrophenyl alpha-D-glucopyranosyluronic acid (PNP-GA), 2-O-alpha- D-glucopyranosyluronic acid-D-xylose (GA-2X), 2-O-(4-O-methyl-alpha-D-glucopyranosyluronic acid)-D-xylose (MeGA-2X), and O-alpha-D-glucopyranosyluronic acid-alpha-D-glucopyranosiduronic acid (GA-GA). The Km (mM) and Vmax (mumol of glucuronic acid formed/mg of enzyme protein/min) toward these substrates were as follows; 0.13 and 3.21 for PNP-GA, 0.33 and 0.089 for GA-2X, 17.6 and 0.094 for MeGA-2X, and 0.36 and 0.015 for GA-GA, respectively. The results indicate that the PNP-GAase specifically hydrolyzed PNP-GA, however, the enzyme had broad substrate specificity.

Synthesis of regioisomeric methyl alpha-L-arabinofuranobiosides.

The three regioisomers of methyl alpha-L-arabinofuranobioside, namely methyl O-alpha-L-arabinofuranosyl-(1-->2)-alpha-L-arabinofuranoside, methyl O-alpha-L-arabinofuranosyl-(1-->3)-alpha-L-arabinofuranoside, and methyl O-alpha-L-arabinofuranosyl-(1-->5)-alpha-L-arabinofuranoside, were synthesized for use as substrates in studies of the specificity of alpha-L-arabinofuranosidase. The regiospecifically protected precursors, namely methyl 3,5-di-O-benzoyl-alpha-L-arabinofuranoside, methyl 2,5-di-O-benzyl-alpha-L-arabinofuranoside, and methyl 2,3-di-O-benzoyl-alpha-L-arabinofuranoside, were prepared from 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl chloride (4) and methyl 5-O-trityl-alpha-L-arabinofuranoside, respectively, and glycosylated with 4 in the presence of silver trifluoromethanesulfonate and s-collidine. 1H and 13C NMR data for all compounds are presented.

Stereoselective synthesis of regioisomers of aldobiouronic acid.

alpha-Glucuronidase is a very important enzyme for the complete hydrolysis of plant hemicellulose, but the substrate specificity of the enzyme has not previously been reported. In this connection, the three regioisomers of O-(alpha-D-glucopyranosyluronic acid)-D-xylose (aldobiouronic acid), 2-O-(alpha-D-glucopyranosyluronic acid)-D-xylose (13), 3-O-(alpha-D-glucopyranosyluronic acid)-D-xylose (14), and 4-O-(alpha-D-glucopyranosyluronic acid)-D-xylose (15), were stereoselectively synthesized to clarify the substrate specificity.

A study of chemoreception based on membrane fluidity and circular dichroism of a membrane assembly model--role of protein penetrating into the lipid bilayer.

We attempted to reconstitute a chemical sensing assembly by mimicking the natural constituents of cell membranes. This liposomal arrangement is able to recognize chemical stimulants by detecting perturbation of the ordered lipid bilayer due to penetration by protein molecules. It was ascertained by measuring membrane fluidity using ESR that this assembly may be able to detect individually added chemical stimulants such as short-chain-bearing odorants (isovaleric acid, isovaleraldehyde, and isoamyl alcohol etc) at a concentration of 3 x 10(-4) parts to 1 part water. This recognition mechanism may clarify both the affinity of chemical stimulants for the liposomal arrangement and the trigger action of conformational changes in poly-L-lysine (PLL) due to the penetration of the bilayer of the PLL and sodium octylsulfate complex.