Effect of high oxygen tension on potassium retentivity and colony formation of baker's yeast

The ability of yeast cells to retain potassium and to form colonies was studied after exposure to pressures ranging from 2 to 143 atmospheres of oxygen. The investigations allow comparison of these responses with those found after x-ray exposure. Exposure to 2 to 8 atmospheres of oxygen for 2, 20, and 40 hours showed decreased potassium leakage as measured by an elution technique. Further experiments using 0.5 to 22 hour exposures to 10 to 143 atmospheres of oxygen showed decreased potassium leakage when glucose was present in the test media, but increased leakage (as did x-ray effects) in the absence of substrate. There was increased potassium leakage into the suspending media (distilled water) during oxygen exposure but this usually did not affect the leakage rates measured subsequently. Marked inability to form colonies was observed after 20 hour exposures to 100 atmospheres of oxygen, with a much smaller response at lower pressures. Increased oxygen concentrations, not pressure, evidently caused these effects, since comparable pressures of nitrogen produced almost no change. The ratio of potassium leakage to survival sensitivity was found to be approximately unity when comparing exposures causing 50 per cent damage. This is quite different from that seen with x-ray or ultraviolet irradiation.

Biosynthesis of S-adenosylmethionine by Saccharomyces cerevisiae. I. Adenine and methionine requirments

Yall, Irving (University of Arizona, Tucson, Ariz.). Biosynthesis of S-adenosylmethionine by Saccharomyces cerevisiae. I. Adenine and methionine requirements. J. Bacteriol. 83:1336-1340. 1962.-Both a parent strain (SC-10) and an adenineless mutant strain (SC-10-80-3-5) of Saccharomyces cerevisiae accumulated S-adenosylmethionine (AM) in the presence of "excess" l-methionine (400 mumoles/100 ml of medium). Relatively small amounts of AM were found when the organisms were grown in the absence of methionine, in the presence of "normal" amounts of l-methionine (3.35 mumoles/100 ml of medium), or in the presence of 400 mumoles of d-methionine. Adenine and hypoxanthine were equally effective in promoting cell growth and AM production in the mutant. S-adenosylmethionine permitted some cell growth. Other purines (guanine and xanthine) and nucleosides such as adenosine and methylthioadenosine did not serve as growth factors. The cell permeability to adenosine was tested by growing the parent strain in the presence of adenosine-8-C(14) and the mutant in adenine and the labeled nucleoside. Both of these experiments were performed in the absence and presence of "excess" l-methionine. Under all conditions, more than 25% of the radioactivity introduced as adenosine-8-C(14) was found in the cells. About 40% of the radioactivity taken up by the mutant cells in the prescene of "excess" l-methionine was fixed in AM. Adenine-8-C(14) was readily taken up by cells of both strains when grown in the absence and presence of "excess" l-methionine. About 17% of the radioactivity taken up by the mutant cells in the presence of "excess" l-methionine was found in the AM fraction.