The influence of growth substrates on metabolic pathways in micrococcus denitrificans

Abstract

1. 1. Autotropically grown M. denitrificans incorporated 14C from 14CO 2 initially into phosphorylated compounds, the chief component of this fraction being 3-phosphoglyceric acid. 2. 2. Extracts of such cells catalysed the incorporation of isotope from NaH 14CO 3 into 3-phosphoglyceric acid, in the presence of ribulose 1,5-diphosphate, or of ribose 5-phosphate + ATP. 3. 3. These results show that autotrophic growth of the organism involves the Calvin cycle of assimilation of carbon dioxide. 4. 4. Extracts of the organisms grown on acetate did not catalyse the incorporations of isotope form NaH 14CO 3 described under 2 above, indicating that the Calvin cycle did not operate under these conditions. 5. 5. Extracts of M. denitrificans grown autotrophically or on a variety of carbon substrates differed in their ability to effect the component reactions of the glyoxylate cycle. Whilst all extracts were qualitatively shown to contain citrate condensing enzyme and malate synthetase, only those from acetate-grown cells contained high isocitratase activity. The activity of glyoxylate cycle enzymes in acetate-grown cells was sufficiently high to account for the growth of M. denitrificans on acetate as sole carbon source. 6. 6. These findings show that change in the mode of growth, from autotrophy to growth on acetate, was accompanied by an alteration of metabolic pathways from Calvin cycle to glyoxylate cycle, and suggest that isocitratase is under adaptive control. 7. 7. Studies on the effect of other carbon sources on the isocitratase formed by acetate-grown cells indicate that they control both the activity and formation of the enzyme by feed-back mechanisms. 8. 8. It is suggested that such feed-back mechanisms control the intracellular operation of the glyoxylate cycle.