Growth of Paracoccus denitrificans on [2,3-13C]succinate and [1,4-13C]succinate. I. The flux of carbon in energy metabolism and the operation of the TCA cycle.

The metabolism of Paracoccus denitrificans, grown on either [2,3-13C]succinate or [1,4-13C]succinate, was investigated by using gas chromatography-mass spectrometry. The distribution of label in a group of metabolites closely related to the TCA-cycle intermediates showed that the flux of carbon from succinate in energy metabolism in vivo was via pyruvate (malic enzyme) and acetyl CoA. The labelling pattern of the carboxyl groups showed that one fifth of the succinate pool was formed by the regeneration of succinate via the TCA cycle, and four fifths was supplied externally as substrate from the medium.