STOPPED-FLOW STUDIES OF THE AEROBIC REDUCTION OF ASCORBIC-ACID OXIDASE

A stop-flow spectrophotometric kinetic investigation of ascorbic acid oxidase using reductic acid as substrate under aerobic conditions at pH 7.0 is presented. The reduction of type-1 (at 610 nm) as well as of type-3 copper (at 330 nm) has been monitored over a wide concentration range of substrate (from 15μM to 3mM). In particular, data are compared with three different substrate concentrations, viz.: (a) under conditions of limiting substrate concentration; (b) under conditions by which the substrate concentration is comparable with the oxygen present in solution; (c) with large excess of substrate. The time course of the reaction is analyzed both in terms of rate and amplitude of the initial fast step(s). Several analogies with laccase (which has already been reported on in the literature) are apparent, despite the different distribution of copper ions in the two cases. However, there are significant differences whose mechanistic significance is not, as yet, understood. © 1979.