Quinoprotein oxidoreductases for the oxidation of alcohols, sugars and amines

Summary

Quinoproteins are enzymes containing a quinone cofactor, that is the non-covalently bound PQQ or the protein-chain-integrated TPQ or TTQ. Quinoprotein dehydrogenases play a role in non-phosphorylative degradation of sugars, alcohols, aldehydes, ketones, and amines by Gram-negative bacteria, providing useful energy to the organism by their capacity to transfer electrons to the respiratory chain. Since the quinoprotein dehydrogenase mostly occurs in high quantity or has a high turnover number, very efficient substrate conversions can be achieved with it, as observed in Pseudomonads, Acetobacters and Gluconobacters. However, since the quinoprotein dehydrogenase always catalyzes the first step and subsequent steps in the route are sometimes lacking or are less efficient, in these cases incomplete oxidation or overproduction occurs, as exemplified by the production of vinegar or gluconic acid. Progress in the enzymology and bioenergetics of these quinoproteins as well as applicational aspects related to enantioselective kinetic resolutions and electrode-directed electron transfer are discussed.

TPQ-containing amine oxidases are widely distributed among prokaryotes and eukaryotes. An efficient method for the isolation of TPQ or hydrazine-derivatizatable cofactors is described.