Metabolism of Aromatic Compounds in Higher Plants

Abstract

In 1908, Rosenthaler (1) described an enzyme in almonds which under appropriate conditions catalyzes the asymmetric synthesis of dextrorotatory benzaldehyde cyanohydrin.This enzyme, which he named oxynitrilase, was subsequently shown to occur in other higher plants (2, 3).Other workers (4, 5) did not accept the existence of an enzyme of this nature.Instead they attributed the asymmetric synthesis to the presence of nonprotein impurities bearing asymmetric centers.Albers and Hamann (6) subsequently established that the enzymatic formation of the dextrorotatory cyanohydrin from benzaldehyde and HCN occurred in the presence of crude enzyme preparations from almonds.They stressed, however, that nonenzymatic synthesis of the racemic mixture occurred simultaneously.The early literature on the occurrence of oxynitrilase and its relation to the general problem of asymmetric synthesis has been reviewed (7, 8).During a study of the biosynthesis of dhurrin, the cyanogenic glycoside (p-hydroxymandelonitrile-/3-n-glucoside)of Sorghum vulgure (9, lo), an enzyme was observed which catalyzes the following reaction:The enzyme has been purified approximately 175-fold from etiolated sorghum seedlings.Some of its properties will be described.