Enhanced Biological Production of L-Cysteine at Ultra-high Substrate Concentrations of D,L-2-amino-Δ2-thiazoline-4-carboxylic acid

L-Cysteine is often used in drug, cosmetics and food industries. The amino acid has been usually produced via acid-hydrolysis of hairs from animals or human. Since there are some problems with chemical methods, such as environmental pollutions and low yield, biological methods are to be developed. There have been reports about biological productions of L-cysteine1),2). However, the substrate concentration levels were so low that the industrial process of L-cysteine production could be not accomplished. In this study, D,L-2-amino-Δ2-thiazoline-4-carboxylic acid (D,L-ATC) was used as the starting substrate of enzymatic reactions for L-cysteine productions. The eutectic melting technique was applied to prepare extremely high concentrated D,L-ATC solutions. Various salts were added for both enzyme stability and formation of eutectic mixtures. Among them, magnesium chloride and sodium carbonate were effective, leading to a eutectic mixture of 2.6 M. And the conversion of D,L-ATC to L-cysteine at ultra-high substrate concentration levels was performed using the whole cells ofZoogloea ramigera as an enzyme source. Approximately 75% conversion was achieved at a substrate level of 0.5 M.