Mechanism of amine oxidation by coenzyme PQQ

Abstract

Chemical behavior of coenzyme PQQ and its analogues toward several amines is reviewed. Product analyses and kinetic studies so far reported indicate that the oxidation of primary amines by pyrroloquinoline quinone derivatives proceeds via the ionic mechanism through the carbinolamine intermediate from which two competing reaction pathways, direct α-proton abstraction and transamination, occur to give the quinol and the aminophenol products, respectively. The similar ionic mechanism through the carbinolamine-type intermediate is proposed for the reactions between PQQ and α,ϵ-diaminoalkanes, hydrazines, and aminoguanidine, where the redox reaction (quinol formation) and adduct formation reactions are controlled by alkylene chain length, electronic nature of the substituents, and pH conditions of the solution, respectively. PQQ catalyzes oxidative decarboxylation and oxidative dealdolation (C αC β bond fission) of α-amino acids, which can be also interpreted by the similar ionic mechaism.