Do Thiol Amino Acids Inhibit Threonine Deaminase Activity in E. coli? (Letter to the Editor).

Cysteine and homocysteine suppress the growth of Escherichia coli. It was explained by the inhibition of threonine deaminase (TD) (Harris in J Bacteriol 145(2):1031-1035, 1981). TD inhibition was detected by a decline in its product, 2-ketobutyrate (2-KB). We propose that cysteine or homocysteine may not inhibit TD activity. Instead, 2-KB binds to them forming stable cyclic adducts. This binding possibly leads to isoleucine limitation and growth inhibition.