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

^a Department of Microbiology and Medical Technology, The University of Arizona, Tucson, Arizona 85721

ABSTRACT

A pink, adenine-requiring yeast utilized adenine, hypoxanthine, or S-adenosylmethionine (SAM), in quantities up to 3 µmoles 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 µmole per 100 ml of medium. However, 6 µmoles 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 µmoles of the amino acid on the utilization of SAM. The presence of 400 µmoles 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-8-¹⁴C. Studies on the uptake of radioactivity from a mixture of SAM-adenine-8-¹⁴C and ³H-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 ³⁵S from ³⁵S-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 µmoles of L-methionine plus adenine even when exogenous SAM was supplied. Approximately 47% of radioactivity fixed from exogenous SAM-adenine-8-¹⁴C and 12% from ³H-labeled SAM-methyl were found in reisolated SAM.

¹ Present address: Department of Biology, New Mexico Highlands University, Las Vegas 87701.

² Present address: Department of Microbiology, Cornell University, Medical College, New York, N.Y. 10021.