SALICORTIN - A REPEAT-ATTACK NEW-MECHANISM-BASED AGROBACTERIUM-FAECALIS BETA-GLUCOSIDASE INHIBITOR

Salicortin, a natural product abundant in most members of the Salicace ae family, is a mechanism-based inactivator of Agrobacterium faecalis beta-glucosidase. Inactivation is delayed in the presence of competiti ve inhibitors, thereby demonstrating the requirement for an enzyme-bou nd salicortin before inactivation. Product studies suggest that inacti vation proceeds via a quinone methide intermediate formed by the fragm entation of the aglycone of salicortin while it is bound to the enzyme . Tryptic digest and HPLC/MS studies confirm the role of quinone methi de attack and also show that the enzyme undergoes multiple modificatio ns. In addition, when the inactivation was run in the presence of a mu tant inactive form of the enzyme, HPLC/MS analyses clearly showed no m odification of the mutant enzyme, demonstrating that the quinone methi de does not exist in free solution and suggesting that inactivation is active-site directed.