Na+-coupled glycine transport in reticulocyte vesicles of distinct sidedness: stoichiometry and symmetry.

Sodium-coupled glycine transport has been studied using membrane vesicles of distinct sidedness, either inside-out or right side-out, prepared from sheep reticulocytes. The activity is chloride dependent and characterized by high and low apparent affinities for glycine (K'm approximately equal to 0.5 mM and greater than 10 mM) for both types of vesicles as well as intact cells. Transport is symmetrical with respect to similar apparent affinity constants for glycine, for both the high- and low-affinity systems, and for sodium. Direct measurements of the sodium/glycine coupling indicate a ratio of 2:1, consistent with kinetic data fitted to a Hill-type equation describing glycine flux as a function of sodium concentration.