Summary
Human blood platelets were suspended in plasma or Krebs solution and incubated with radiolabeled glycylglycine or glycylproline in order to study cellular uptake. Platelets accumulated radioactivity against a concentration gradient. In the case of glycylglycine, uptake was not inhibited by cold, or metabolic inhibitors. Uptake of radioactivity derived from glycylglycine or glycylproline did not appear to involve saturable mechanisms since the platelet content of radioactivity was directly related to medium concentration even at high concentrations.
Chromatographic identification of radioactivity in cells and incubation media showed the glycylglycine was not extensively hydrolysed; 80 per cent of platelet radioactivity was intact dipeptide. With glycylproline, cellular radioactivity was entirely 14C-glycine. There was no direct evidence that this dipeptide actually entered the cells, and we could not determine whether entry did occur with subsequent hydrolysis, or whether hydrolysis preceded uptake.
