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Biosynthesis of serine in Neurospora crassa
Two pathways for serine biosynthesis in Neurospora crassa have been reported by Sojka and Garner. The phosphorylated pathway involves 3-phosphoglyceric acid, phosphohydroxypyruvic acid, and phosphoserine as intermediates, whereas the non-phosphorylated pathway involves glyceric acid and hydroxypyruvic acid as intermediates (1)The phosphorylated pathway was suggested to be the major pathway of serine biosynthesis in Neurospora by these authors. In this investigation a serine-requiring mutant of Neurospora crassa was mapped on linkage group V and was studied in order to determine the nature of its biochemical lesion. Each enzyme in the two postulated pathways was extracted from the mutant strain and compared with the extract of the corresponding enzyme from the nutritionally wild-type strain of Neurospora crassa from which the mutant was originally derived. All enzymes involved in the two pathways were comparable in activity in the mutant and in the wild-type, indicating that the serine requirement in the mutant does not arise from the loss or alteration of any of the enzymes in these two pathways.