Interaction of a Chick Skin Collagen Fragment (all-CB5) with Human Platelets

The denatured al(I) chain and the cyanogen bromide peptide, @l(I)-CB5, of chick skin collagen cause the release of serotonin and leakage of lactic dehydrogenase from human platelets in a manner similar to the release reaction mediated by adenosine diphosphate and native collagen. These peptides also cause a decrease in the level of adenosine 3’:5’-monophosphate (CAMP) in platelets. Adenylate cyclase activity of platelets is partially inhibited by these peptides as well as by native collagen, ADP, and epinephrine, but CAMP phosphodiesterase activity is unaltered by these substances. In contrast, the level of platelet guanosine 3’:5’-monophosphate (cGMP) is increased by the collagen peptides as well as the other aggregating agents. The increase is associated with increased guanylate cyclase, but normal cGMP phosphodiesterase activities of platelets. Optical rotatory and viscometric measurements of the cul chains and al-CB5 of chick skin in 0.01 M phosphate/O.15 M sodium chloride, pH 7.4, at various temperatures as a function of time indicate that no detectable renaturation occurs at 37” for at least 30 min of observation. Molecular sieve chromatography of cul-CB5 in the phosphate buffer at 37” shows that its elution position is identical to that performed under denaturing conditions (at 45”) with no evidence of higher molecular weight aggregates, and the c~l-CB5 glycopeptide fraction eluting from the column at the position of its monomer retains the platelet aggregating activity. Additionally, electron microscopic examination of the platelet-rich plasma that had been reacted with these peptides fail to show any ordered collagen structures. These data indicate that the denatured cul chain and al-CBS glycopeptide of chick skin collagen mediate platelet aggregation through the “physiologic” release reaction in a manner similar to that induced by other aggregating agents such as ADP, epinephrine, or native collagen, and support the conclusion that the aggregating activity of the otl chain and otl-CB5 is not likely to be due to the formation of polymerized products.