Interactions between potassium ions and glycine transport in the yeast Saccharomyces carlsbergensis

A study has been made of the effects of both varying the pH and extracellular [K + ] on the initial rate of uptake of glycine ( v ) by a strain of Saccharomyces carlsbergensis that concentrated the amino acid, with respect to the extracellular phase, by up to 1400 times. When no other substrate than glycine was provided and [glycine] was relatively small (≤0.2mm) (1) v increased fivefold when the pH was lowered from 7 to 4.5; (2) v fell by up to about 80% as [K + ] rose, K + behaving as a non-competitive inhibitor of the system, with K i 0.33mequiv./l at pH7; (3) the absorption of glycine caused up to about 2 or 3 equiv. of K + to leave the yeast cells. These three phenomena were each less evident when glucose was present. An analogy is drawn between the respective interactions of H + and K + with the yeast system and the well recognized effects of Na + and K + on amino acid transport in certain mammalian systems.