Characterization of Pyridoxine Auxotrophs ofEscherichia coli: Serine and PdxF Mutants

At least six phenotypically distinct classes of mutants ofEscherichia coli which require serine or pyridoxine or both can be isolated. Three of the six classes lack 3-phosphoserine-2-oxoglutarate aminotransferase. One of these classes contains WG5, a mutant previously characterized as containing thepdxF5 allele. The aminotransferase isolated from this mutant has been compared to that isolated from wild-typeE. coli and found to have apparently normal affinity for pyridoxal 5′-phosphate, but reduced affinity for pyridoxamine 5′-phosphate.