Interactions of poly (L-lysine) with human platelets. Correlation of binding with induction of platelet aggregation

Abstract Poly(L-lysine) (PLL) was iodinated with 125 I by use of the Bolton and Hunter reagent. Use of 125 I-PLL permitted demonstration of the binding of this cationic polymer to platelets. 125 I-PLL binds to freshly isolated viable platelets, paraformaldehyde-fixed platelets, isolated platelet plasma membrane preparations, and fixed plasma membrane preparations. Determination of affinities of binding suggests the possibility of at least two classes of binding sites for PLL. The binding is inhibited competitively by unlabeled PLL but displacement of bound PLL is complicated by the aggregation of platelets that occurs in the presence of large amounts of added unlabeled PLL. Succinylation of ϵ-amino groups of PLL results in complete loss of binding of the polymer to platelets. Binding of 125 I-PLL is not affected by the presence of EDTA, adenosine, prostaglandin E 1 , cyclic 2′3′ AMP, or acetyl-salicyclic acid, and none of these agents have an effect on PLL-induced platelet aggregation. When studies were conducted with PLLs of different average molecular weights (MW), it was observed that 68,000 MW PLL has a significantly greater binding affinity than either 30,000 MW or 6,200 MW PLLs. When the platelet aggregation-inducing abilities of different MW PLLs were compared with their binding affinities, it was observed that the molecular size of PLL that caused maximal aggregation at minimal molar concentration also exhibited the greatest deqree of binding.