Metabolic pathways and biotechnological production of L-cysteine.

L-Cysteine is an important amino acid both biologically and commercially. Although most amino acids are commercially produced by fermentation, cysteine is mainly produced by protein hydrolysis. However, synthetic or biotechnological products have been preferred in the market. Biotechnological processes for cysteine production, both enzymatic and fermentative processes, are discussed. Enzymatic process, the asymmetric hydrolysis of DL-2-amino-Delta(2)-thiazoline-4-carboxylic acid to L-cysteine, has been developed and industrialized. The L-cysteine biosynthetic pathways of Escherichia coli and Corynebacterium glutamicum, which are used in many amino acid production processes, are also described. These two bacteria have basically same L-cysteine biosynthetic pathways. L-Cysteine-degrading enzymes and L-cysteine-exporting proteins both in E. coli and C. glutamicum are also described. In conclusion, for the effective fermentative production of L-cysteine directly from glucose, the combination of enhancing biosynthetic activity, weakening the degradation pathway, and exploiting the export system seems to be effective.