Kinetics and Mechanism of the Oxidative Deamination of Amines by Coenzyme PQQ

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Abstract
Kinetic studies on the oxidative deamination of amines by coenzyme PQQ are carried out under anaerobic conditions. The reaction is first-order in the appearance of the reduced PQQ and in the total amine concentrations. A large kinetic isotope effect (kH⁄kD=7.24) in the oxidation of α,α-dideuteriobenzylamine indicates that the C–H bond cleavage is a rate-determining step. From the results of formation of two types of reduced PQQ (quinol and aminophenol) and low reactivities of secondary and tertiary amines, we propose the mechanism via covalent addition of the amine to the quinone followed by rate-limiting α-proton removal.