Response of the intracellular adenosine triphosphate pool of Saccharomyces cerevisiae to growth inhibition induced by excess L-methionine.

Yeast cells accumulate S-adenosyl-l-methionine (S-AM) when cultivated in the presence of l-methionine. Cell growth is inhibited by the addition of high concentrations of l-methionine. A number of investigators have attributed this to the depletion of adenosine triphosphate (ATP) as a consequence of the utilization of that mucleotide for S-AM formation. The cellular ATP pool of Saccharomyces cerevisiae was measured during growth inhibition caused by addition of excess l-methionine. Polyethylenimine thin-layer chromatography and subsequent autoradiography were used to quantitate the extracted ATP. Addition of l-methionine to a level of 5 mg/ml in a culture during exponential growth caused an increase in the doubling time of 40 to 50%. During this period, the cellular ATP level continued increasing normally and, as the cells entered stationary growth, receded to a level characteristic of an uninhibited stationary culture growth. After the addition of methionine, there was never an observed depletion of the ATP pool other than the normal fluctuation which occurs in an uninhibited culture. We have concluded that growth inhibition by excessive methionine does not result from limiting availability of ATP.