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 (PubMed:1646200, PubMed:7592433, PubMed:8617755, PubMed:9878716, PubMed:18838797). 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) (PubMed:8617755, PubMed:9878716, PubMed:18838797). 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 (PubMed:9878716). The electrons transfer occurs from ubiquinol (QH2) to the additional heme c within subunit II (AdhB) (PubMed:8617755, PubMed:9878716). Also able to use quinone analogs such as 2,3-dimethoxy-5-methyl-6-n-decyl-1,4-benzoquinone (DB) and 2,3-dimethoxy-5-methyl-6-n-pentyl-1,4-benzoquinone (PB) (PubMed:9878716). 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. 2,6-dichloro-4-dicyanovinylphenol (PC16) and antimycin A inhibit ubiquinol oxidation activity more selectively than the ubiquinone reductase activity. Optimum pH is 5 for ubiquinol oxidation activity. The alcohol dehydrogenase multicomponent enzyme system is composed of a dehydrogenase subunit I (AdhA), a cytochrome c subunit II (AdhB) and a subunit III (AdhS). Constitutively expressed. Inactive ADH is produced under conditions of low pH and high aeration, where the bypass oxidase activity is highly elevated. In spite of having 10 times less enzyme activity than active ADH, inactive ADH is not distinguished from active ADH with respect to their subunit compositions, molecular sizes and prosthetic groups. It seems that in inactive ADH, an improper interaction between subunit II and subunit I/III complex impairs efficient intersubunit electron transport in the ADH complex. Belongs to the bacterial PQQ dehydrogenase family.