Tryptophanase and amino acids. Amino acids that have an asymmetric C at the .beta.-position (L-threonine, L-allothreonine, L-isoleucine, .beta.-methyl-L-tryptophan) and some other amino acids (L-valine, phenylglycine, glycine) did not evoke this 500 nm peak. Bromopyruvate was a very potent inactivator of TPase. PLP completely prevented this inactivation, but inhibitor amino acids did not. One SH group per subunit of TPase was blocked by treatment with bromopyruvate. The cysteine residue that reacts is probably located in the peptide T-18-1 isolated by others. TPCK inactivated TPase in a manne similar to bromopyruvate.