The Role of Collagen Quaternary Structure in the Platelet:Collagen Interaction

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RESUMO

We have investigated whether collagen queternary structure is required for the platelet: collagen interaction. Quaternary structure refers to the assembly of collagen monomers (tropocollagen) into polymers (native-type fibrils). Purified monomeric collagen was prepared from acetic acid extracts of fetal calfskin. Polymeric collagen was prepared by dispersion of bovine Achilles tendon collagen and by incubation of monomeric collagen at 37°C and pH 7.4. The state of polymerization was confirmed by electron microscopy. Release of platelet serotonin in the absence of platelet aggregation was used to determine the effectiveness of the platelet: collagen interaction. All forms of collagen produced serotonin release only after a lag period, but polymeric collagen gave a shorter lag period than did monomeric collagen. Monomeric collagen was also quanidinated selectively to convert collagen lysine groups to homoarginine, while leaving the arrangement of polar groups intact. Guanidination of monomeric collagen increased the rate of polymerization and reduced the lag time in serotonin release. Glucosamine (17 mM) retarded polymerization and inhibited the release of platelet serotonin by monomeric collagen but had little effect on release produced by thrombin or polymeric collagen. At the same concentration, glucosamine did not reduce the sensitivity of platelets to stimulation by collagen or block the platelet: collagen interaction. The only effect of glucosamine was on the collagen: collagen interaction. Galactosamine had a similar effect, but glucose, galactose, and N-acetylglycosamine had no effect. We conclude from this data that collagen monomers cannot effectively interact with platelets and that, therefore, collagen quaternary structure has a role in the recognition of collagen by platelets.

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