Abstract
Acetic acid bacteria are able to oxidize various sugars and sugar alcohols and such oxidative reactions are called "oxidative fermentation", since they catalyze incomplete oxidation of individual substrates accompanied by accumulation of the corresponding oxidation products in huge amounts in the growth medium. Many numbers of cytosolic NAD(P)-dependent enzymes and membrane-bound NAD(P)-independent enzymes were purified to clarify the mechanism of the oxidative fermentation. As the results, the oxidative fermentation is catalyzed only by the membrane-bound dehydrogenases accompanying bioenergy generation. Unexpectedly, NAD(P)-dependent cytosolic enzymes have no relation to the oxidative fermentation. Pyrroloquinoline quinone (PQQ), a novel coenzyme was discovered from various membrane-bound dehydrogenases and the total figure of the oxidative fermentation was depicted based on the results obtained as the periplasmic oxidation system. An interesting physiological property of PQQ as the growth stimulating substance for microorganisms is also briefly described.
