Global Control of Proline Dehyrogenase in Escherichia Coli
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Proline dehydrogenase (PDH) is a membrane-bound enzyme involved in the two step degradation of L-proline in enterobacteria. Activity of PDH in E. coli was studied in a variety of growth conditions in order to investigate global controls known to influence activities of degradative enzymes. First, the effects of catabolite repression produced by glucose-6-phosphate, glucose, gluconate, mannitol, sodium succinate, fructose, glycerol, glucosamine, and sodium accetate were studied. The results showed that L-proline dehydrogenase like B-galactosidase is subject to catabolite repression. Secondly, nitrogen repression by ammonium was studied in media containing either glucose or glycerol as the carbon source. A fifty-fold increase in ammonium concentration resulted in a twofold decrease of PDH activity in glycerol and no repression in glucose. Lastly, PDH activity was measured in several independent cultures containing substrates for other membrane bound dehydrogenases. Dehydrogenases for D-alanine, L-Lactate, L-proline and fatty acids showed competitive behavior for membrane binding; PDH activity decreased over a 6-fold range with the induction of membrane-bound dehydrogenases.