The role of the telopeptide region of collagen in the platelet-collagen interaction

Removal of the telopeptide regions by pepsin inhibits platelet aggregation and release by monomeric collagen in PRP. This inhibitory effect appears to be due to the inability of pepsin modified collagen to form fibrils in plasma, since fibrils formed in buffer cause aggregation and [ 14C] serotonin release in PRP. Fibrils formed from pepsin modified collagen appear to be quantitatively more effective in causing platelet aggregation and serotonin release than normal fibrils. When pepsin modified collagen is studied as a function of time of digestion, there is a dissociation between platelet aggregation and release. Fibrils formed from pepsin modified collagen become quantitatively more effective the longer the duration of digestion. Platelet aggregation but not release by fibrillar collagen can be inhibited by a 14 fold excess of pepsin soluble collagen. This effect can be overcome by increasing the concentration of fibrillar collagen. Pepsin modified soluble collagen appears to cause serotonin release of gel filtered platelet but not aggregation. These data suggest that the telopeptide regions play a role in collagen quaternary structure and that the atelopeptide tropocollagen may bind to the platelet but is not sufficient to produce platelet aggregation.