Evaluation of D‐amino acid oxidase from Rhodotorula gracilis for the production of α‐keto acids: A reactor system

Abstract

The study reports on the development of a bioreactor for the production of α‐keto acids from D,L‐ or D‐amino acids using Rhodotorula gracilis D‐amino acid oxidase. D‐Amino acid oxidase was co‐immobilized with catalase on Affi‐Gel 10 matrix, and the reactor was operated as a continuous‐stirred tank reactor (CSTR) or stirred tank with medium recycling conditions. The optimum substrate concentration and quantity of biocatalyst were determined (5 mM and 1.2 mg/L, respectively). Under optimum operating conditions, product formation was linearly related to both substrate and enzyme concentration, showing the system to be highly flexible. Under these conditions, in a stirred tank, over 90% conversion was achieved in 30 min with a maximum production of 0.23 g of pyruvic acid/day/enzyme units. Product was recovered by ion exchange chromatography. The operational stability of the reactor was high (up to 9.5 h of operation without loss of activity) and the inactivation half‐life was not reached even after 18 h or 36 bioconversion cycles. This represents the first case of a reactor developed successfully with a D‐amino acid oxidase. © 1994 John Wiley & Sons, Inc.