Effect of l -Methionine and S -Adenosylmethionine on Growth of an Adenine Mutant of Saccharomyces cerevisiae

Abstract

methionine (SAM), in quantities up to 3 Amoles per 100 ml of medium, as equivalent sources of purine for cell growth, but not methylthioadenosine or S-adenosylhomocysteine. Utilization of SAM for growth was inhibited by the presence of L-methionine in quantities greater than 0.6 ,mole per 100 ml of medium. However, 6 ,umoles of L-methionine had no effect on growth when adenine or hypoxanthine was the source of purine. These sources also reversed the inhibitory effects of 6 ,umoles of the amino acid on the utilization of SAM. The presence of 400 ,umoles of the amino acid resulted in some inhibition of growth when the organisms were grown with adenine, hypoxanthine, or adenine plus SAM but had no effect on the total uptake of adenine-8-'4C. Studies on the uptake of radioactivity from a mixture of SAM-adenine-8-'4C and 8H-labeled SAM-methyl indicated that these components were taken into the cells at different rates which were altered by the presence of L-methionine. The fixation of I'S from "5S-labeled adenosylmethionine into the cells was inhibited by the presence of the amino acid. The cells synthesized and accumulated SAM in the presence of 400 ,umoles of L-methionine plus adenine even when exogenous SAM was supplied. Approximately 47% of radioactivity fixed from exogenous SAM-adenine-8-'4C and 12% from 8H-labeled SAM-methyl were found in reisolated SAM. Yall (12) reported that an adenineless mutant of Saccharomyces cerevisiae (SC-10-80-3-5) and its parent strain (SC-10) accumulated relatively large amounts of S-adenosylmethionine (SAM) when grown in a synthetic medium containing 400 0,moles ("excess" amounts) of L-methionine

Active Transport of Exogenous S -Adenosylmethionine and Related Compounds into Cells and Vacuoles of Saccharomyces cerevisiae

“…However, S-adenosyl-D-homocysteine, in contrast to S-adenosyl-D-methionine, is taken up at a much lower rate. The rapid assimilation of S-adenosyl-L-homocysteine is in agreement with earlier observations on other strains of S. cerevisiae (4,22). S-adenosyl-L-homocysteine was degraded very fast, and no conclusion could be drawn concerning its penetration into the vacuole.…”

“…The examination of C. utilis in this respect was disappointing; the uptake and accumulation remained low (12). More encouraging results were obtained with Saccharomyces cerevisiae by Yall (4,22) and by Spence (5,18) and their co-workers who studied several features of the specificity and mechanism of active transport by the cytoplasmic membrane. It was not possible, however, to draw conclusions on the intracellular distribution or accumulation of the material in the vacuole, because the level remained too low to permit conclusive ultraviolet micrography.…”

Response of the Intracellular Adenosine Triphosphate Pool of Saccharomyces cerevisiae to Growth Inhibition Induced by Excess l -Methionine

“…In the presence of excess L-methionine, there is a large accumulation of S-AM in yeast (10,11). Since ATP is required for the conversion (2), previous investigators have suggested that depletion of the intracellular ATP pool due to overproduction of S-AM causes the observed inhibition (5,(13)(14)(15). Thus far, however, no direct evidence has been presented showing that the ATP pool is depleted.…”

Biological Uptake of Phosphorus by Activated Sludge 1

“…Determinations of pH were made with a pH meter (Leeds and Northrup Co., Philadelphia, Pa.). Radioactive assays were made in a Tri-Carb liquid scintillation counting system (model 314 (Packard Instrument Co., Downers Grove, Ill.)), using techniques that have been described (10). All counts were corrected for decay.…”