EVALUATION OF D-AMINO-ACID OXIDASE FROM RHODOTORULA-GRACILIS FOR THE PRODUCTION OF ALPHA-KETO ACIDS - A REACTOR SYSTEM

This study reports on the development of a bioreactor for the producti on of a-keto acids from D,L- or D-amino acids using Rhodotorula gracil is 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 cont inuous-stirred tank reactor (CSTR) or stirred tank with medium recycli ng conditions. The optimum substrate concentration and quantity of bio catalyst were determined (5 mM and 1.2 mg/L, respectively). Under opti mum operating conditions, product formation was linearly related to bo th substrate and enzyme concentration, showing the system to be highly flexible. Under these conditions, in a stirred tank, over 90% convers ion was achieved in 30 min with a maximum production of 0.23 g of pyru vic acid/day/enzyme units. Product was recovered by ion exchange chrom atography. The operational stability of the reactor was high (up to 9. 5 h of operation without loss of activity) and the inactivation half-l ife was not reached even after 18 h or 36 bioconversion cycles. This r epresents the first case of a reactor developed successfully with a D- amino acid oxidase. (C) 1994 John Wiley & Sons, Inc.