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 C₁ compounds has been investigated by brief incubation of bacterial suspensions with [2,3-¹⁴C₂]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 [2,3-¹⁴C₂]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 [2-¹⁴C]serine from [2,3-¹⁴C₂]succinate in wild-type Pseudomonas AM1, and of [2-¹⁴C]serine and [2-¹⁴C]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 C₄ skeleton between C-2 and C-3, rather than by a direct combination of two C₁ units derived from the growth substrate. 6. The cleavage mechanism is quantitatively more significant during growth on methanol than on succinate.