Studies on human platelets. I. Synthesis of platelet protein in a cell-free system

A reproducible cell-free system, active in protein synthesis, has been prepared from human blood platelets. The ability of this system to incorporate 14 C-labeled amino acids, is dependent on the presence of ribosomes, a soluble enzyme fraction (S-150), and ATP plus an ATP-generating system. Both puromycin and ribonuclease have the ability to inhibit amino acid incorporation. A major soluble protein product of this system has been characterized; the solubility properties, sucrose gradient patterns, and fingerprint patterns of the 14 C-labeled soluble product appear identical to the [ 14 C]actomyosin-like contractile protein isolated from labeled, intact platelets.