ABSTRACT
Quinoproteins are considered to be proteins with either pyrroloquinoline quinone or a similar quinone structure as prosthetic group and so will include methylamine dehydrogenase as well as the quinoprotein dehydrogenases responsible for oxidation of glucose, methanol, and ethanol. In all systems studied it has been found that soluble cytochromes c and blue copper proteins are located exclusively in the periplasm, and membrane-bound cytochrome c is most commonly part of a cytochrome bc 1 complex. When available, evidence for the involvement of the quinoprotein in establishing a protonmotive force are discussed. It is usually emphasized in discussions of electron transfer systems of methylotrophs that they contain large amounts of c-type cytochromes. The route for electron transport from ethanol depends on the type of dehydrogenase involved. The alcohol dehydrogenases from acetic acid bacteria differ from the soluble enzymes in being membrane-bound hemoquinoprotein complexes.
