Studies on the proteins of human platelet membranes.

Isolated human platelet membranes which have been analyzed by sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis have been shown to contain a heterogeneous group of polypeptides of different molecular weight classes ranging from 10,000 to over 250,000. Three major glycoproteins have been identified in the platelet membrane. Some of the architectural relationships of the platelet membrane polypeptides were probed by analysis of the residual protein gel patterns following incubation of the intact cells with proteolytic enzymes. The membrane polypeptides in their native state in intact cells were relatively resistant to low dose Pronase digestion in contrast to the high sensitivity of the isolated membrane fragments to enzyme digestion. The membrane glycoproteins in intact cells were particularly susceptible to trypsin and papain action. Acetylcholinesterase was a readily accessible membrane constituent which was rapidly inactivated by small amounts of Pronase. N-Ethyl[W]maleimide and [203Hg]p-chloromercuribenzene sulfonate labeling of intact whole platelets revealed three major membrane polypeptides with reactive sulfhydryl groups. Isotopic labeling of one of these membrane polypeptides was partially blocked by prior incubation of washed platelets with anti-F(ab’)z thrombosthenin fragments.