The Triton X - 100 - Insoluble Residue ( “ Cytoskeleton ” ) of Aggregated Platelets Contains Increased Lipid Phosphorus as Well as ‘ 251 - Labeled Glycoproteins

When ‘25l-labeled blood platelets were lysed with an equal volume of 2% Triton X-100, 10 mM EGTA, and 100 mM Tris, pH 7.4. the Triton-insoluble residue (“cytoskeleton”) contained about 1 1 % of the platelet protein. predominantly actin and actin-binding protein, 3.5% of the platelet radioactivity, and less than 2% of the platelet lipid phosphorus. Radioautographs of polyacrylamide gels of this residue (reduced samples) differed markedly from those of whole platelets. Glycoprotein lIb (mol wt 1 21 .000) was not detected and GP Ill (mol wt 107.000) was seen in trace amounts if at all. The amounts of the other labeled glycoproteins in the Triton-insoluble residue were estimated by scanning the radioautographs and comparing the area for each band with that of the similar band in whole platelet samples. In 1 1 experiments. 38% of GP IV (mol wt 89.000). 8% of the GP at mol wt 132,000 and 56% of the GP at mol wt 1 58.000 were insoluble in Triton. Since no glycoproteins were evident between about mol wt 90,000 and 1 70,000 in unreduced samples of these residues, the identity of the most abundant Triton-insoluble glycoprotein was unclear. In platelets stimulated with thrombin. Tritoninsoluble protein increased to 1 6.7%, due at least in part to the formation of fibrin from platelet fibrinogen; it did not increase in platelets stimulated with ADP. The amount of Triton-insoluble radioactivity and lipid phosphorus, and the gel pattern of Triton-insoluble radioactive proteins was