Isolation of a platelet membrane protein which binds the platelet-activating factor...

The phospholipid platelet-activating factor 1-0-hexadecyl-2-acetyl-SN-glycero-3-phosphorylcholine (AGEPC) initiates platelet function by interacting specifically with 1399 +/- 498 (mean +/- SD) high-affinity membrane receptors per platelet. In studies designated to characterize the high affinity binding site, AGEPC-human serum albumin-Sepharose was employed to isolate a 180,000 mol. wt. protein from human platelet plasma membranes. Platelet plasma membranes were isolated by adsorption of sonicated human platelets to a column of wheat germ agglutinin-Sepharose and elution with N-acetyl-glucosamine. The plasma membranes were solubilized in 5% sodium dodecyl sulphate and applied to a column of AGEPC-human serum albumin-Sepharose. After washing the column extensively, the specifically bound material was eluted with a five-fold molar excess of AGEPC. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of the eluted material revealed a single protein with an apparent molecular weight of 180,000. This protein was not recovered from solubilized platelet membranes when chromatography was performed with a column of human serum albumin-Sepharose lacking AGEPC. The capacity of this protein to bind AGEPC suggests that it represents a constituent of the human platelet receptor for AGEPC.