CONTINUOUS L-CYSTEINE PRODUCTION USING IMMOBILIZED CELL REACTORS AND PRODUCT EXTRACTORS

Methods to improve the stability of L-cysteine-producing enzymes from Pseudomonas sp. M-38, both as whole cells and as immobilized cells, we re investigated for the production of L-cysteine from D,L-2-amino-Delt a(2)-thiazoline-4-carboxylic acid (D,L-ATC). Among the three L-cystein e-producing enzymes only L-ATC hydrolase was unstable. However, the st ability of L-ATC hydrolase was significantly enhanced by the addition of 20% sorbitol. In continuous L-cysteine production, more than 60% of the initial activity of L-ATC hydrolase remained after 1000 hours at 37 degrees C with 40% sorbitol and at 30 degrees C with 20% sorbitol. A system involving a cascade of processes using two packed-bed reactor s with immobilized cells and two L-cysteine extractors with the ion-ex change resin Dowex 50W was developed to reduce product inhibition and unreacted substrate. The overall productivity of the system was 43% hi gher than for two reactors without an ion-exchange extractor. Copyrigh t (C) 1997 Elsevier Science Ltd.