A Catalytic Mechanism for Benzylamine Oxidase from Pig Plasma

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Abstract
Ammonium ion is shown to decrease the rate constants for Schiff''s base formation and formation of a reduced intermediate during the catalytic cycle of benzylamine oxidase from pig plasma. The rate constant for reoxidation of the reduced intermediate is also inhibited while the rate constant for conversion of the oxidized enzyme form back to native enzyme is stimulated by ammonium ion. Ammonium ion changes the EPR spectrum of the cupric centers in the enzyme, indicating that ammonia binds to the Cu. A catalytic mechanism for benzylamine oxidase is proposed on the basis of these and other results. This mechanism includes a novel step in which a hydroxyl coordinated to Cu acts as a nucleophile to facilitate hydride ion transfer to oxygen during the reoxidation process.