Cyanogenesis in Sorghum vulgare—III. : Partial purification and characterization of two β-glucosidases from Sorghum tissues

Abstract

Two β- D-glucopyranosidase activities with distinct aglycone specificities were characterized in Sorghum vegetative tissues and seeds. Glucosidase I, which was assayed with p-nitrophenyl α- D-glucopyranoside, also hydrolyzes salicin, but not dhurrin ( p-hydroxy- L-mandelonitrile β- D-glucopyranoside). It was concentrated 10-fold and obtained free of β-glucosidase II. Glucosidase II was assayed with dhurrin; it hydrolyzes other mandelonitrile and benzyl β-glucosides as well. Glucosidase II was purified 85-fold from vegetative tissues and 4-fold from seeds, in which it occurs in higher concentrations, but it was not obtained free of glucosidase 1. The pH optima and Michaelis constants of the two glucosidases for their respective assay substrates are reported, as well as K i values for several competitive inhibitors. Sorghum oxynitrilase decomposes the L-isomer of p-hydroxymandelonitrile.