The ethanol oxidase respiratory chain of Gluconobacter suboxydan was characterized by using G. suboxydans subsp. alpha, a variant species of G. suboxydans incapable of oxidizing ethanol. The membranes of G. suboxydans subsp. alpha exhibited neither alcohol dehydrogenase, ethanol oxidase, nor glucose-ferricyanide oxidoreductase activity. Furthermore, the respiratory chain of the organism exhibited an extremely diminished amount of cytochrome c and an increased sensitivity of the respiratory activity for cyanide or azide when compared with G. suboxydans. The first-subunit quinohemoprotein and the second-subunit cytochrome c of alcohol dehydrogenase complex in the membranes of G. suboxydans subsp. alpha were shown to be reduced and deficient, respectively, by using heme-staining and immunoblotting methods. Ethanol oxidase activity, lacking in G. suboxydans subsp. alpha, was entirely restored by reconstituting alcohol dehydrogenase purified from G. suboxydans to the membranes of G. suboxydans subsp. alpha; this also led to restoration of the cyanide or azide insensitivity and the glucose-ferricyanide oxidoreductase activity in the respiratory chain without affecting other respiratory activities such as glucose and sorbitol oxidases. Ethanol oxidase activity was also reconstituted with only the second-subunit cytochrome c of the enzyme complex. The results indicate that the second-subunit cytochrome c of the alcohol dehydrogenase complex is essential in ethanol oxidase respiratory chain and may be involved in the cyanide- or azide-insensitive respiratory chain bypass of G. suboxydans.