This family consists of several bacterial Malate:quinone oxidoreductase (Mqo) proteins (EC:1.1.99.16). Mqo takes part in the citric acid cycle. It oxidises L-malate to oxaloacetate and donates electrons to ubiquinone-1 and other artificial acceptors or, via the electron transfer chain, to oxygen. NAD is not an acceptor and the natural direct acceptor for the enzyme is most likely a quinone. The enzyme is therefore called malate:quinone oxidoreductase, abbreviated to Mqo. Mqo is a peripheral membrane protein and can be released from the membrane by addition of chelators [1].

1: Biochemical and genetic characterization of the membrane-associated malate dehydrogenase (acceptor) from Corynebacterium glutamicum. Molenaar D, van der Rest ME, Petrovic S; Eur J Biochem 1998;254:395-403. PMID:9660197