The Action of the $-Glucosidase\; of\; Staohybotrys\; Atra\; on\; P-Nitrophenyl\; P-Quinovoside$

Abstract

p-Nitrophenyl /l-D-quinovopyranoside has been prepared and found to be a substrate for S. atra /l-glucosidase. The affinity of the enzyme for this substrate was an order of magnitude less than for p-nitrophenyl /l-glucoside, but of the same order as for many ortho-substituted aryl /l-glucosides. The Michaelis constant was 3·4 X 1O-4M (3·2 X 1O-5M for p-nitrophenyl /l-glucoside); the ratio V:h.x.!V~ax. was 0 ·20 for the two p-nitrophenyl glycosides. It was rather difficult to make accurate measurements with the quinovoside since it was fairly unstable in aqueous solution. The rate of spontaneous decomposition of its solutions in distilled water (pH about 5·5) was some 20 times that of solutions of the glucoside.