Growth of Paracoccus denitrificans on [2,3-13C]succinate and [1,4-13C]succinate. II. Isoleucine biosynthesis.

Paracoccus denitrificans was grown on either [2,3-13C]succinate or [1,4-13C]succinate, and extracts were analysed by using gas chromatography-mass spectrometry. The distribution of label in isoleucine indicated that the 2-ketobutyrate required for isoleucine biosynthesis was mainly produced from pyruvate by 2-keto-acid chain elongation (i.e. the 'pyruvate elongation pathway'). Approximately 10% of isoleucine was produced by a second pathway involving propionyl CoA. Threonine and glutamate were not utilized by P. denitrificans as a source of 2-ketobutyrate production for isoleucine biosynthesis under the growth conditions used.