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Characterization of Pyridoxine Auxotrophs of Escherichia coli: Serine and PdxF Mutants

At least six phenotypically distinct classes of mutants of Escherichia 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 the pdxF5 allele. The aminotransferase isolated from this mutant has been compared to that isolated from wild-type E. coli and found to have apparently normal affinity for pyridoxal 5′-phosphate, but reduced affinity for pyridoxamine 5′-phosphate.