Energy Generation and the Glucose Dehydrogenase Pathway in Acinetobacter

Abstract

Direct, non-phosphorylative, bacterial glucose oxidation was discovered nearly half a century ago (Barron and Friedemann, 1941; Lockwood et al., 1941). The possession of such a property was deduced from the fact that gluconic and ketogluconic acids were formed from glucose. The first step in this pathway is the oxidation of glucose at the C1 position to form 1,5-gluconolactone, which is hydrolysed by enzyme action or spontaneously to form gluconic acid; direct glucose oxidation can also occur at other positions, but these conversions are not relevant here. The reaction is catalysed by a glucose dehydrogenase, whereas glucose oxidase (EC 1.1.3.4) occurs only in yeasts and fungi. The enzyme belongs either to the category of NAD(P)-dependent dehydrogenases or to the dye-linked dehydrogenases. In the former case, NAD(P) is reduced in the reaction and then re-converted into NAD by the NADH dehydrogenase of the respiratory chain; in the latter case, the reduction equivalents on the cofactor are directly transferred in vivo to a component of the respiratory chain, and in vitro to an artificial dye. During the 1950’s, the latter type of glucose dehydrogenase was discovered in many Pseudomonas and Acetobacter strains, and also in Bacterium anitratum. It should be noted that the bacterial dehydrogenase discussed here is not the flavoprotein glucose dehydrogenase (EC 1.1.99.10) which has only been reported to occur in Aspergillus oryzae (Bak, 1967).