Platelet-reactive sites in collagen. Collagens I and III possess different aggregatory sites

Collagen type III possesses a highly reactive platelet-aggregatory site at a locus which in type I is essentially inactive whilst the latter collagen possesses reactive sites absent in type III. It is proposed that platelet aggregation by collagen involves the sequence GK[or R]PG(EY)GPK[or R]G(EY) or, less favourably, GPK[or R]G(EY)G(XY)GK[or R]PG(EY), one basic residue acting in combination with the second in an adjacent alpha-chain.