ABSTRACT
This chapter describes the structures and functions of the two bacterial quinoproteins, glucose dehydrogenase and alcohol dehydrogenase. Therefore, the dehydrogenase subunit is considered a quinohemoprotein, and alcohol dehydrogenase of acetic acid bacteria should be referred to as a quinohemoprotein-cytochrome c alcohol dehydrogenase complex. Thus, the quinohemoprotein dehydrogenase subunit of alcohol dehydrogenase of acetic acid bacteria is considered a conjugated product of a quinoprotein part and a cytochrome c part. However, the enzyme shows a lower optimum pH of 4-6 and relatively restricted substrate specificity compared with quinoprotein or quinohemoprotein alcohol dehydrogenase; it oxidizes only primary alcohols from ethanol to hexanol, but not methanol or secondary or tertiary alcohols, and shows some activity for formaldehyde and acetaldehyde. There are several other enzymes related to the quinoprotein alcohol dehydrogenase described, which include aromatic alcohol, polyethylene glycol, and polyvinyl alcohol dehydrogenases. There is little information on the coupling of alcohol dehydrogenases to the respiratory chain.
