Masao Shimada

Enzymatic Production of L-Cysteine with Tryptophan Synthase of Escherichia coli

Abstract Tryptophan synthase of Escherichia coli catalyzes the synthesis of l -cysteine from various β-substituted- l -alanines (e.g., l -serine) and sulfides (e.g., sodium hydrosulfide). Not only l -serine but also O- methyl- l -serine , O- acetyl- l -serine , β-chloro- l -alanine, l -serine O-sulfate, S- methyl- l -cysteine , O- benzyl- l -serine and S- benzyl- l -cysteine could be used as a substrate for l -cysteine synthesis. l -Serine was the best substrate. The rate of l -cysteine formation from l -serine and sodium hydrosulfide with tryptophan synthase was 47% of that of tryptophan formation from l -serine and indole. Under optimum conditions established for l -cysteine production, 114 g/l of l -cysteine was formed in a molar yield of 94% based on l -serine added. Enzymatically synthesized l -cysteine was confirmed to be L-form after isolation and identification of the product.

Production of S-(carboxymethyl)-L-cysteine from L-serine with tryptophan synthase

Abstract Synthesis of S -carboxymethyl)- l -cysteine ( l -CMC) from L-serine with tryptophan synthase was studied. In the β-replacement reaction l -serine catalyzed by tryptophan synthase of Escherichia coli , thioglycolic acid was a poor substrate but alkylthioglycolates were good substrates. S -(2-Ethylhexyloxycarbonylmethyl)- l -cysteine was synthesized from l -serine and 2-ethylhexylthioglycolate using intact cells of recombinant E. coli with high tryptophan synthase activity, and subsequently hydrolyzed to l -CMC with alkali in one reactor. Under optimum conditions established for l -CMC synthesis, 159 g. l −1 of l -CMC was formed at a molar yield of 94% based on when both l -serine and 2-ethylhexylthioglycolate were added. Synthesized l -CMC was confirmed to be l -form after isolation and identification of the product.