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  • Title: Active site-directed modification of tryptophanase by 3-bromopyruvate.
    Author: Honda T, Tokushige M.
    Journal: J Biochem; 1985 Mar; 97(3):851-7. PubMed ID: 3894342.
    Abstract:
    Tryptophanase purified from Escherichia coli B/It7-A was irreversibly inactivated by 3-bromopyruvate following pseudo-first-order kinetics. The inactivation rate for the holoenzyme tended to saturate as the concentration f bromopyruvate increased. L-Alanine and DL-3-phenylserine, potent competitive inhibitors with respect to L-tryptophan decomposition, protected the enzyme from inactivation. Titration of SH groups in the enzyme protein with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) showed that modification of one SH group per enzyme subunit resulted in a complete inactivation. When the enzyme was subjected to bromopyruvate-modification following pretreatment with DTNB, the activity was almost completely restored upon reduction with dithiothreitol. Modification of the enzyme with bromopyruvate quenched the absorption peak near 500 nm, characteristic of a quinoidal structure formed by labilization of the alpha-proton. These results support the possibility that bromopyruvate reacts with the enzyme as an affinity labeling agent.
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