Metabolism of serine and glycine in E. coli K12. I. The role of formate in the metabolism of serine–glycine auxotrophs

Certain auxotrophs of E. coli K12 have a nutritional requirement for serine, glycine, or sodium formate. Formate is not a precursor of either serine or glycine; serine is a precursor of some but not all glycine. These findings do not fit in with the phosphorylated pathway of serine biosynthesis frequently postulated. A hypothesis is made that formate reactivates an otherwise nonfunctional enzyme of serine biosynthesis. This is only one of several possible hypotheses. Complications of intermediary metabolism of serine and glycine are considered in some detail. The conclusion is reached that this area of metabolism is less well understood than is frequently thought.