Binding of beta 2-glycoprotein I to platelets: effect of adenylate cyclase activity
Schousboe, I.
Thrombosis Research 19(1-2): 225-237
1980
ISSN/ISBN: 0049-3848 PMID: 7444854 Document Number: 161428
.beta.2-glycoprotein I was trace-labeled with 3H by reductive methylation. It bound specifically to washed human platelets. No binding was measured to erythrocytes and only insignificantly small amounts were bound to lymphocytes. Bound and free [3H] .beta.2-glycoprotein I were measured after separation from the suspending medium by centrifugation. Maximum binding was obtained within 45 min and was proportional to the number of platelets in the incubation mixture. Equilibrium binding was established with reequilibration after dilution. Analysis of .beta.2-glycoprotein I as a function of .beta.2-glycoprotein I concentration indicates that platelets bind 6 .times. 105 .beta.2-glycoprotein I molecules/platelet at saturation with an apparent dissociation constant of 559 nM. In the presence of Ca2+, a significantly lower amount of .beta.2-glycoprotein I is bound with an apparent dissociation constant of 334 nM. Platelets treated with formalin bind more .beta.2-glycoprotein I than do untreated platelets, but the dissociation constant is unaffected by the formalin treatment. Neuraminidase treatment of the platelets has no effect on the binding. The presence of other serum proteins in binding assays performed at 25.degree. C has no effect on the binding. The binding of .beta.2-glycoprotein I to the platelets can be correlated with inhibition of adenylate cyclase activity.