K CAT Inactivation of mushroom polyphenol oxidase

Abstract

Listen

Translate article

Mushroom polyphenol oxidase is rapidly inactivated during turnover of substrate to product ( k cat inactivation). As shown by use of [U- 14C]-phenol as substrate, there is a marked nonspecific covalent binding of product to polyphenol oxidase (85 mol 14C-labeled product per mol of polyphenol oxidase subunits). In the presence of sufficient ascorbic acid to keep the product o-benzoquinone reduced to dihydroxyphenol, only 0.04 mol of 14C-labeled product per mol of polyphenol oxidase subunits was covalently bound. Therefore, k cat inactivation of mushroom polyphenol oxidase probably involves a free radical mechanism, rather than covalent binding of product at the active site proposed as one mechanism by Wood and Ingraham [5].