Mechanism of inactivation and identification of sites of modification of ornithine aminotransferase by 4-aminohex-5-ynoate

The inactivation of ornithine aminotransferase by an enzyme-activated irreversible inhibitor 4-aminohex-5-ynoate was accompanied by stoichiometric binding of the radiolabeled compound. Distribution of radiolabel among separated tryptic peptides indicated that more than one amino acid residue had reacted. Lys-292 and Cys-388 were positively identified. Reduction with borohydride was necessary to stabilize the adduct formed with Lys-292, and the relevant peptide prepared after this treatment contained equimolar amounts of inhibitor and coenzyme. The coenzyme chromophore in this peptide showed strong negative circular dichroism. A mechanism consistent with these observations is proposed.