The Concentration of Glycine by Saccharomyces uvarum: Role of the Main Vacuole and Conditions Leading to the Explosive Absorption of the Amino Acid

Abstract

At pH 4.3 in the presence of 2% (wt/vol) glucose and 13 mM-glycine, washed cells of S. uvarum took up and retained a maximum of about 1 .mu.mol glycine/mg dry wt. A steady state was reached in which glycine influx was < 10% of its initial value and was largely balanced by the rate of glycine metabolism, efflux being slow. Controlled lysis 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 an N source led to marked changes: the initial rate of glycine uptake doubled; the amount of glycine retained increased to > 2 .mu.mol mg-1; glycine entered the vacuoles causing them to swell; and many of the cells swelled and burst. The general amino-acid permease apparently concentrated glycine by a factor of about 5 .times. 104 at the plasmalemma. The amount of glycine taken up was regulated by osmotic factors and access to the vacuole.