The isolation of a peptide from the catalytic domain of Bacillus stearothermophilus tryptophyl-tRNA synthetase. The interaction of Brown MX-5BR with tyrosyl-tRNA synthetase.

Tryptophyl-tRNA synthetase is irreversibly inactivated by Procion Brown MX-5BR with an apparent dissociation constant (KD) of 8.8 microM and maximum rate of inactivation k3 0.192 s-1. The specificity of the interaction is supported by two previously reported observations. Firstly, Brown MX-5BR inactivation of tryptophyl-tRNA synthetase is inhibited by substrates, and secondly, the animated derivative of Brown MX-5BR is a competitive inhibitor of tryptophyl-tRNA synthetase with a Ki of 2 X 10(-4) M with respect to both tryptophan and ATP. Tryptic digestion of the dye-affinity-labelled enzyme and subsequent resolution of the peptides by h.p.l.c. yielded one major dye-peptide peak. Amino acid sequence analysis resulted in the identification of the dye-binding domain centred on lysine-178. Tyrosyl-tRNA synthetase is also inactivated by Procion Brown MX-5BR, and this inactivation is prevented by ATP but not by tyrosine. The interaction of tyrosyl-tRNA synthetase with hydroxylated Brown MX-5BR exhibited non-competitive kinetics with respect to the amino acid-binding site and competitive kinetics against ATP with a Ki of 6 X 10(-6) M.