Kinetic study of soybean beta-amylase. The effect of pH

1) Beta-Amylase [EC 3.2.1.2] was prepared from defatted hawk eye soybean flour. The enzyme concentration dependence of the initial velocity for the hydrolytic reaction was investigated at pH 5.4 in the range of the enzyme concentration from 6.6 x 10(-10) M to 5.0 x 10(-6) M. It was found that the initial velocity was proportional to the enzyme concentration in this range. 2) The hydrolyses of maltodextrin (DPn = 74.4) and soluble starch catalyzed by soybean beta-amylase were investigated in the pH range from 3.0 to 9.1 at 25 degrees C, and the Michaelis constant, Km, and the maximum velocity, V, for each substrate were determined at each pH. The pH-rate profile showed a bell-shaped curve, and the pH "optimum" was at 5.85. From Dixon plots of V and V/Km, the pK values were found to be 3.5 and 8.2 for the free enzyme, and 3.5 and 8.5 for the enzyme-substrate complex. The pH-rate profile in the presence of 25% methanol (v/v) was also obtained at alkaline pH. The pKe values were the same as those in the absence of methanol. Based on these results, it was estimated that the ionizable acidic group was an amino group and the basic group was a carboxyl one.

Hydrolysis of phenyl beta-maltoside catalyzed by saccharifying alpha-amylase from Bacillus subtilis

1. The hydrolytic reaction of phenyl beta-maltoside catalyzed by saccharifying alpha-amylase [EC 3.2.1.1] of Bacillus subtilis was studied at 25 degrees C and pH 5.4, by measuring the total reducing power and the amount of phenol liberated, and by thin layer chromatography. 2. The enzyme hydrolyzed phenyl beta-maltoside at the glucosidic linkage between the two glucose residues to form D-glucose and phenyl beta-D-glucoside. Besides these products, maltose, maltotriose, and phenyl beta-maltotrioside were also observed as reaction products. The identification of phenyl beta-maltotrioside is described in detail. The formation of these products was attributed to the transglycosylation reaction of the enzyme. The time course of reaction as followed by reducing power measurement showed an induction period of several minutes.

L-amino acid dehydrogenases in Bacillus subtilis spores

The presence of two kinds of l-amino acid dehydrogenase in resting spores of Bacillus subtilis was indicated. One of them was l-alanine dehydrogenase, which used only l-alanine as a substrate, and the other was nonspecific dehydrogenase, which used l-valine, l-isoleucine, l-leucine, and l-alanine (slightly) as substrates. Several properties of these dehydrogenases were compared.