The effect of chemical or enzymatic modifications upon the ability of collagen to form multimers and to initiate platelet aggregation

Abstract

The previous paper (1) presented some correlations between collagen multimer formation and platelet aggregation. The present study investigates the effect of chemical or enzymic modification upon its melting temperature and rate of multimerization, and therefore upon platelet aggregation. Digestion of collagen with tadpole or bacterial collagenase led to a decreased melting point of the collagen fragments and prevented their initiation of platelet aggregation. In contrast, the absence of interchain crosslinks, in lathyritic collagen, had no effect on these parameters and thus these crosslinks are not required for collagen multimer formation and induction of platelet aggregation. Oxidation of the galactoses alone with galactose oxidase, or of all the sugars by periodate, led to a perturbed melting curve featuring two melting points, ∼ 28° and 37°. These treated collagen preparations were thus unable to form multimers at platelet aggregation (> 29°) temperatures, and they could not initiate the aggregation of platelets. Reduction with sodium borohydride regenerated a normal melting curve, multimerization, and platelet aggregation initiation. Thus the carbohydrate residues, and a majority of the intact tropocollagen chains, are required for the maintenance of native structure and of multimerization at 37° which, in turn, are necessary for initiation of platelet aggregation by guinea pig skin collagen.