Diversity of limited oxidations accomplished by gluconobacter oxydans

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Virginia Tech

Gluconobacter oxydans is characterized by the ability to carry out rapid, single-step oxidations of many different hydroxyl-containing compounds. These oxidations are believed to be catalyzed by the membrane-bound NAD(P)-independent dehydrogenases. Experiments were designed to use G. oxydans ATCC strain 621 to determine the contribution of these dehydrogenases in whole-cell oxidations and to determine the range of substrates that can be oxidized by the membrane fraction of these cells when grown on a single substrate. My first hypothesis was that the membranes would accomplish these oxidations at the same rate as an equivalent number of whole cells. Oxidative activity data obtained from using both oxygen uptake and tetranitroblue tetrazolium assays, however, did not support this hypothesis. I attribute this to the probability that the membranes were damaged during isolation of the membrane fraction and, therefore, were unable to exhibit full oxidative potential. My second hypothesis was that the membranes from cells grown on one substrate would oxidize many other substrates. Potassium fenicyanide was used to assay the oxidative activity of the membrane fraction of cells grown on glycerol. Of 41 substrates tested all were significantly oxidized. I concluded from these data, therefore, that the enzyme(s) responsible for the oxidation of these substrates are synthesized constitutively. Unfortunately, one cannot draw any conclusions as to whether or not these enzymes are highly substrate-specific. I speculate that one or a few enzymes show a broad range of substrate specificity, as it would be inefficient for the cell to consecutively synthesize more than forty different substrate-specific enzymes for substrates it may never encounter.