Glycine formation during growth of Pseudomonas AM1 on methanol and succinate

1. The mechanism of regeneration of glycine during the growth of Pseudomonas AM1 on C(1) compounds has been investigated by brief incubation of bacterial suspensions with [2,3-(14)C(2)]succinate and observing the incorporation of radioactivity into various metabolites. 2. With the wild-type organism growing on methanol, radioactivity appeared rapidly in glycine and tricarboxylic acid-cycle intermediates, but there was a relatively slow labelling of serine and phosphorylated compounds. Serine became labelled predominantly in the C-2 position. 3. The proportion of radioactivity incorporated into glycine at earliest times was greatly diminished when succinate-grown cells were used. 4. Radioactivity was also incorporated from [2,3-(14)C(2)]succinate into glycine and serine by methanol-grown mutant 20S, which lacks phosphoserine phosphohydrolase. Both the glycine and serine were labelled mainly in C-2. 5. The formation of predominantly [2-(14)C]serine from [2,3-(14)C(2)]succinate in wild-type Pseudomonas AM1, and of [2-(14)C]serine and [2-(14)C]glycine in the mutant lacking the phosphorylated pathway from succinate to serine, is taken as strong evidence for a mechanism of glycine regeneration involving cleavage of a C(4) skeleton between C-2 and C-3, rather than by a direct combination of two C(1) units derived from the growth substrate. 6. The cleavage mechanism is quantitatively more significant during growth on methanol than on succinate.