Regulation of C1 metabolism by l-methionine in Saccharomyces cerevisiae

摘要

p1. The concentrations of folate derivatives in aerobic cultures of iSaccharomyces cerevisiae/i (A.T.C.C. 9763) were determined by microbiological assay employing iLactobacillus casei/i (A.T.C.C. 7469) and iPediococcus cerevisiae/i (A.T.C.C. 8081). Cells cultured in media lacking l-methionine contained higher concentrations of folate derivatives than cells grown in the same media supplemented with 2.5μmol of l-methionine/ml. The concentrations of highly conjugated derivatives were also decreased by supplementing the growth medium with l-methionine. 2. DEAE-cellulose column chromatography of extracts prepared from cells grown under these conditions revealed that the concentrations of methylated tetrahydrofolates were drastically decreased by the methionine supplement. Smaller decreases were also observed in the concentrations of formylated and unsubstituted derivatives. 3. The concentrations of four enzymes of Csub1/sub metabolism were compared after 6h of growth in the presence and in the absence of l-methionine (2.5μmol/ml). The specific activities of formyltetrahydrofolate synthetase, methylenetetrahydrofolate reductase and serine hydroxymethyltransferase were not altered by this treatment but that of 5-methyltetrahydrofolate–homocysteine methyltransferase was decreased by approx. 65% when l-methionine was supplied. The activities of 5-methyltetrahydrofolate–homocysteine methyltransferase, serine hydroxymethyltransferase and formyltetrahydrofolate synthetase were not appreciably altered by l-methionine iin vitro/i. In contrast this amino acid was found to inhibit the activity of methylenetetrahydrofolate reductase. 4. Feeding experiments employing sodium [sup14/supC]formate indicated that cells grown in the presence of exogenous methionine, although having less ability to convert formate into methionine, readily incorporated sup14/supC into serine and the adenosyl moiety of iS/i-adenosylmethionine. 5. It is suggested that exogenous l-methionine controls Csub1/sub metabolism in iSaccharomyces/i principally by regulation of methyl-group biogenesis within the folate pool./p