On the Inactivation of Ascorbic Acid Oxidase by Wendell H. Powers and Charles R. Dawson

An outstanding characteristic of the enzymatic oxidation of ascorbic acid by highly purified preparations of ascorbic acid oxidase, is the pronounced inactivation of the enzyme that occurs during the course of the reaction (1). I t is the purpose of this communication to present data showing that the enzyme inactivation occurring during the reaction, is due to causes which, for the purposes of discussion and clarification, may be divided into two categories: (1) Inactivation due to environmental conditions during the reaction; i.e., pH, substrate concentration, dilution, rate of shaking, etc., and (2) inactivation due to some factor inherent in the ascorbic acid-ascorbic acid oxidase-oxygen reaction. The first type of inactivation may be minimized by the use of the inert protein gelatin in the enzyme dilution under a prescribed set of environmental conditions (1). The second type of inactivation is not minimized to any great extent by the use of added gelatin. The groundwork for a study of the latter type of inactivation of ascorbic acid oxidase was laid by Steinman and Dawson (2), when they reported that catalase, peroxidase, and methemoglobin markedly protect ascorbic acid oxidase against inactivation. Inactivation encountered under various environmental conditions will be discussed first.