SUMMARY: At pH 4-3 in the presence of 2% (w/v) glucose and 13 mm-glycine, washed cells of Saccharomyces uvurum took up and retained a maximum of about I μmol glycine per mg dry wt. A steady state was reached in which glycine influx was less than 10 % of its initial value, and was largely balanced by the rate of glycine metabolism, efflux being slow. Controlled Jysis of the plasmalemma with cytochrome c indicated that little glycine entered the main vacuole. Preliminary starvation of the yeast for 70 min in the presence of glucose without a nitrogen source led to marked changes: the initial rate of glycine uptake doubled; the amuunt of glycine retained increased to more than 2 μmol mg; glycine entered the vacuoles causing them to swell; and many of the cells swelled and burst. The observations indicated that the general amino-acid permease concentrated glycine by a factor of about 5 × 10 at the plasmalemma. The amount of glycine taken up was regulated by both osmotic factors and access to the vacuole.


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