Mechanism of inactivation of monoamine oxidase by trans-2-phenylcyclopropylamine and the structure of the enzyme-inactivator adduct

Mitochondrial monoamine oxidase was inactivated with 2-[2-¹⁴C]phenylcyclopropylamine, dialyzed, and treated with acidic 2,4-dinitrophenylhydrazine. Contrary to the report of Paech et al. (Paech, C., Salach, J.I., and Singer, T.P. (1980) J. Biol. Chem. 255, 2700-2704), the 2,4-dinitrophenylhydrazone obtained was not that of 2-phenylcyclopropanone, but rather of cinnamaldehyde. Furthermore, denaturation of the labeled enzyme in the presence of sodium borohydride resulted in retention of 5.6 times more radioactivity than in its absence. Based on these results, a mechanism of inactivation of monoamine oxidase by 2-phenylcyclopropylamine and the structure of the enzyme-inactivator adduct are proposed.