Dehydrogenase component of the alcohol dehydrogenase multicomponent enzyme system which is involved in the production of acetic acid and in the ethanol oxidase respiratory chain. Quinohemoprotein alcohol dehydrogenase (ADH) catalyzes the oxidation of ethanol to acetaldehyde by transferring electrons to the ubiquinone embedded in the membrane phospholipids. The electrons transfer from ethanol to membranous ubiquinone occurs from pyrroloquinoline quinone (PQQ) to one heme c in subunit I (AdhA), and finally to two heme c in subunit II (AdhB). Besides ubiquinone reduction, ADH also has a ubiquinol (QH2) oxidation reaction which mediates electron transfer from ubiquinol to the non-energy generating bypass oxidase system. The electrons transfer occurs from ubiquinol (QH2) to the additional heme c within subunit II (AdhB). a ubiquinone + ethanol = a ubiquinol + acetaldehyde Binds 1 PQQ group per subunit. Binds 1 Ca(2+) ion per subunit. Binds 1 heme c group covalently per subunit. The alcohol dehydrogenase multicomponent enzyme system is composed of a dehydrogenase subunit I (AdhA) and a cytochrome c subunit II (AdhB). Belongs to the bacterial PQQ dehydrogenase family.