The concentration of glycine by preparations of the yeast Saccharomyces Carlsbergensis depleted of adenosine triphosphate: Effects of proton gradients and uncoupling agents

Abstract

1. At pH 4.5 and 30degreesC, yeast preparations depleted of ATP in the presence of antimycin and deoxyglucose spontaneously lost K⁺, gaining roughly an equivalent amount of H⁺. 2. Five proton conductors including azide and 2,4-dinitrophenol accelerated this process, as did [¹⁴C]glycine, which was absorbed with two extra equivalents of H⁺. 3. The rate of glycine uptake at pH 4.5 diminished fourfold when cellular K⁺ fell by 20%. 4. The distribution of [¹⁴C]propionate indicated that the intracellular pH fell from 6.2 to 5.7 when the cellular content of K⁺ fell by 30%. 5. Glycine uptake from a 5 muM solution was about 400 times faster at pH 4.5 than it was at pH 7.4 with 100mM-KCl present ostensibly to lower the membrane potential. 6. Yeast preparations containing 2mM-[¹⁴C]glycine absorbed a further amount from a 0.1 muM solution at pH 4.5. After about 10 min a net movement of [¹⁴C]glycine out of the yeast occurred. The ratio of the cellular [14Ia1glycine concentration to the concentration outside the yeast reached 4 × 10⁴ in these assays, whereas at pH 7.4 in the presence of 100mM-KCl it did not exceed 15 in 3h. Dimitrophenol lowered the accumulation ratio at pH 4.5, apparently by causing proton conduction. 7. The observations are consistent with the notion that glycine uptake is driven by a proton symport mechanism. 8. Possible factors governing the strikingly low rate of glycine efflux as opposed to its optimum rate of influx are discussed.