Summary
Human blood platelets resuspended in calcium-free Krebs solution accumulated radioactive
L-leucine and L-arginine. The tissue/medium concentration ratio (Ci/Co) was greater than 10:1 when Co was 10–7 M or lower. Accumulation was inhibited by incubation at 4° C, the presence of metabolic
inhibitors or platelet soniñcation at the beginning of the experiment. It is considered
that these compounds are accumulated by energy-dependent processes against a concentration
gradient.
In the presence of 19 other amino acids accumulation of leucine or arginine was greatly
reduced. Under these conditions some incorporation of radioactivity into proteins
occurred. However, incorporation was small. Both compounds were incorporated similarly
despite the fact that arginine is metabolized to ornithine, whilst leucine has no
detectable metabolites. This fact is discussed in relation to the possible physiological
significance of platelet protein synthesis.
