FATTY ACID DEGRADATION IN CAULOBACTER CRESCENTUS (LIPID METABOLISM, OXIDATION ENZYMES)
O'CONNELL, MARY ANNE
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The pathway of fatty acid utilization was investigated in Caulobacter crescentus. Two strains of C. crescentus were shown to utilize fatty acids as sole carbon source and five enzymes involved in a (beta)-oxidation degradative pathway were identified in cell extracts. These included, acyl-CoA synthase; acyl-Co dehydrogenase; enyol-CoA hydratase; 3-hydroxyacyl-CoA dehydrogenase; and 3-ketoacyl-CoA thiolase. The activities of these enzymes were higher in C. crescentus than the fully induced levels observed in Escherichia coli. Growth in glucose or glucose plus oleic acid decreased fatty acid uptake and lowered the specific activity of the enzymes involved in (beta)-oxidation by 2- to 3-fold, in contrast to the 50-fold glucose repression found in E. coli. The mild glucose repression of the acyl-CoA synthetase was reversed by exogenous dibutyryl cyclic AMP. Acyl-CoA synthetase activity was shown to be the same in oleic acid-grown cells and in cells grown in the presence of succinate. Thus, fatty acid degradation by the (beta)-oxidation pathway is constitutive in C. crescentus and is only mildly affected by growth in the presence of glucose.;Tn5 insertion mutants unable to form colonies when oleic acid was the sole carbon source were isolated. These mutants efficiently transported fatty acids and had (beta)-oxidation enzyme levels comparable with that of the wild type. Our inability to obtain fatty acid degradation mutants, coupled with the high constitutive levels of the (beta)-oxidation enzymes, suggest that fatty acid turnover might play an essential role in membrane biogenesis and cell cycle events in C. crescentus.;The enzymes of the (beta)-oxidation pathway in C. crescentus were characterized and three of the enzymes were purified. The purification scheme allowed the co-purification of crotonase, 3-hydroxyacyl-CoA dehydrogenase, and thiolase. The relative heat stability of thiolase allowed its purification to near homogeneity. These three enzymes form a multienzyme complex in E. coli, but a similar complex was not observed in C. crescentus. Instead, separate proteins are present with different enzymatic activities, in a manner similar to the (beta)-oxidation enzymes that have been isolated from higher eukaryotes. In these cells, as in C. crescentus, the individual enzymes form multimers of identical subunits.
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