SUMMARY: strain H16 formed key enzymes of autotrophic metabolism during heterotrophic growth. The formation of the soluble and membrane-bound hydrogenases, ribulose-5-phosphate kinase and ribulosebisphosphate carboxylase were investigated. In addition, selected enzymes shared by autotrophic and heterotrophic carbon metabolism were examined. Key enzymes of autotrophic metabolism were not detected during exponential growth on succinate, pyruvate or acetate, but were found at intermediate activities in cells grown on fructose, gluconate or citrate. Growth with succinate at a suboptimal pH of 7.7 resulted in a decreased growth rate and a marked increase of enzyme activities. Oxygen-limited growth with succinate also led to a derepression of the synthesis of the hydrogenases and the key enzymes of the Calvin cycle. During growth on glycerol or formate, the activities of these enzymes were comparable with those found under autotrophic conditions with H and CO.

The results indicate that both the hydrogenases and the key enzymes of the Calvin cycle were formed under conditions of limited availability of energy. Molecular hydrogen was not required for the formation of the hydrogenases. The regulation of the gluconeogenetic enzymes, common to both autotrophic and heterotrophic carbon metabolism, was more balanced. An increase of enzyme activities was observed under autotrophic conditions, in accord with the physiological role of these enzymes under autotrophic and heterotrophic growth conditions.


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