Abstract
The α2β2 complex of tryptophan synthase from Escherichia coli catalyzes β-replacement reactions of L-serine and its derivatives (e.g., β-chloro-L-alanine and O-methyl-DL-serine) with various alkanethiols. The products from thiobenzyl alcohol and ethanethiol were isolated to demonstrate the enzymatic synthesis of the corresponding S-substituted L-cysteines. Reactivities of various S-substituent donors were examined, and thiols such as thiobenzyl alcohol, 1-propanethiol and 1-butanethiol were found to be much more efficient substituent donors than the physiological substrate, indole. In addition, tryptophan synthase catalyzes β-replacement reactions of L-threonine with thiols to form the corresponding S-substituted β-methylcysteines, which are also produced by β-addition reactions of L-vinylglycine with thiols. These enzymatic reactions facilitate the synthesis of various sulfur-containing amino acids.
