Membrane fluidity and platelet fibrinogen receptor exposure by proteolytic enzymes

Incubation of platelets with pronase or chymotrypsin results in the exposure of fibrinogen receptors. We determined that these enzymes did not affect the membrane fluidity as evaluated by the depolarization of the fluorescence of 1,6-diphenyl-1,3,5 hexatriene (DPH). There was no significant difference in either the depolarization or in its temperature dependence for control, pronase or chymotrypsin-treated platelets. Thus, it can be concluded that the exposure of fibrinogen receptors on the platelet surface by proteolytic enzymes does not depend on the changes of membrane fluidity. We also propose that the proteolytic enzymes do not cause a major alteration in the extent of protein chains embedded in the lipid layers of the platelet membranes.