BIOSYNTHESIS OF SERINE IN ESCHERICHIA COLI AND SALMONELLA TYPHIMURIUM

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Abstract
Evidence for the operation in extracts of E. coli of a pathway from glucose to serine involving 3-phosphoglycerate, phosphohydroxypyruvate and phosphoserine as intermediates was obtained by the technic of isotopic competition. The steps of the pathway were demonstrated in extracts of E. coli and S. typhimurium. The first reaction was studied in the reverse of the biosynthetic direction by observing the disappearance of reduced nicotinamide-adenine-dinucleotide in the presence of phosphohydroxypyruvate. The enzyme catalyzing this reaction was missing in two E. coli mutants that required serine or glycine for growth and in a representative of one of two genetically distinct classes of S. typhimurmm serine-glycine auxotrophs. The second reaction, the amination of phosphohydroxypyruvate, was also studied in the reverse of the bio-synthetic direction using [alpha]-ketoglutarate as the amino-acceptor in a transamination reaction with phosphoserine. The final step, the cleavage of phosphoserine, could not be catalyzed by extracts prepared from cells of S. typhimurium serine-glycine auxotrophs of the second genetic class. It was concluded that these three reactions provide the only significant pathway to serine in these organisms.

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