A method for demonstrating the heterogeneity of pigeon red cell membrane vesicles based on their glycine transport activity.

A procedure is described which is capable of detecting the changes in size and/or density of small membrane vesicles resulting from solute uptake. Vesicles which have taken up solute sediment more slowly in a density gradient, the ratio of glycine uptake/vesicle-trapped space is not uniform in the vesicle population, and vesicles with higher uptake/space ratios are preferentially retarded upon centrifugation. Alanine transport activity is associated with glycine transport activity in that retardation of vesicles due to glycine uptake equally retards vesicles possessing alanine uptake activity.