Glycine synthesis in a Neurospora mutant deficient in serine hydroxymethyltransferase

概要

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Serine hydroxymethyltransferase (SHMT), commonly implicated in the glycine synthesis of eucaryotes, was examined in Neurospora crassa, wild type (FGSC 853) and a formate-requiring mutant (FGSC 9) . The mutant was SHMT-deficient, containing only 15% of the total activity found in the wild type. Differential and density gradient centrifugations showed the mutant to be deficient in soluble SHMT activity. Both strains contained particulate SHMT which sedimented with mitochondrial marker enzymes. The origins of glycine were examined by a combination of enzyme, growth and ^<14>C feeding experiments. Growth of the mutant was strongly inhibited by the isocitrate lyase-directed inhibitor itaconate. This inhibition was reduced when exogenous glycine was supplied. Itaconate (up to 30 mM) did not inhibit growth of the wild type but in both strains isocitrate lyase activities were reduced. The mutant contained more lyase and glyoxylate aminotransferase than the wild type. In feeding experiments, [2-^<14>C]acetate and [1-^<14>C]glyoxylate were more readily incorporated into glycine in the mutant than the wild type. Itaconate (30 mM) reduced the flow of acetate carbon into glycine by up to 70% in the mutant. It is concluded that deficiency in soluble SHMT necessitates glycine synthesis via an isocitrate→glyoxylate→glycine sequence.
日本植物生理学会の論文