Stoichiometry of the topa quinone biogenesis reaction in copper amine oxidases

The stoichiometry of the topa quinone biogenesis reaction in phenylethylami ne oxidase from Arthrobacter globiformis (AGAO) has been determined. We hav e shown that the 6e(-) oxidation of tyrosine to topa quinone (TPQ) consumes 2 mol of O-2 and produces 1 mol of H2O2/mol of TPQ formed. The rate of H2O 2 production is first-order (k(obs) = 1.0 +/- 0.2 min(-1)), a rate only sli ghtly lower than the rate of TPQ formation directly determined previously ( k(obs) = 1.5 +/- 0.2 min(-1)). This gives the following net reaction stoich iometry for TPQ biogenesis: E-Tyr + 2O(2) --> E-TPQ + H2O2. This stoichiome try is in agreement with recently proposed mechanisms for T-PQ biogenesis, and rules out several possible alternatives.