Effect of extracellular pH on the respiratory chain and energetics of Gluconobacter suboxydans.

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Abstract
Gluconobacter suboxydam contains a large amount of cytochrome c in addition of cytochrome o in the respiratory chain of the membrane. The content of cytochrome c was found to be influenced by the extracellular pH in growth which is lowered by oxidation products of several sugars or sugar alcohols in the growth medium. Lowering of the external pH caused an increase in cytochrome c content concomitantly with an increase in alcohol dehydrogenase activity, while neither cytochrome o content nor glucose dehydrogenase activity is increased. The increase in cytochrome c content was also accompanied by an increase in KCN-insensitivity for the respiratory activity. The change in cytochrome c content appeared to be mainly due to the change of a cytochrome c corresponding to the second subunit of alcohol dehydrogenase. Furthermore, the extracellular pH of G. suboxydans also affected a respiration-driven proton translocation; the H+ /O ratio of the cells grown at lower pH was much lower than the value, about 2, of the cells grown at higher pH. In the presence of KCN, however, both the cells grown at high and low pHs could not generate a membrane potential. Thus, this study indicates that G. suboxydans produces a KCN-insensitive and non-energy-generating respiratory bypass, which may be related to a cytochrome c associated with alcohol dehydrogenase, concomitant with a decrease of the extracellular pH during growth.

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