Myrosinase is regarded as a defense-related enzyme in the Brassicaceae and is capable of hydrolyzing glucosinolates into various compounds, some of which are toxic. Severa1 myrosinase isoenzymes exist, and some of them have been found in association with nonmyrosinase proteins. One of these associated proteins, myrosinase-associated protein (MyAP), was purified from seeds of Brassica The myrosinase-glucosinolate system is a preformed, two-component system that is activated upon tissue damage, whereby enzymatic decomposition of glucosinolates by the myrosinase enzyme takes place. Glucosinolates and their hydrolysis products are claimed to function as a defense against generalized herbivores and are implicated as a factor in host-plant recognition by specialized consumers (Chew, 1988;Louda and Mole, 1991). Myrosinase (thioglucoside glucohydrolase, EC 3.2.3.1) consists of a group of isoenzymes capable of hydrolyzing the thioglucoside bond in glucosinolates. The resulting aglycones rearrange spontaneously and yield, in addition to sulfate, compounds such as isothiocyanates, organic thiocyanates, epithionitriles, and nitriles. Within individual plants of a species, several different types of glucosinolates exist. The exact outcome of the reaction depends on a number of factors '