A Study of Polymerization Sites in Bovine Fibrinogen

Abnormalities in bovine fibrinogen polymerization have been brought about by slight proteolysis on the native molecule by two purified aminopeptidases that we have called A and B and which come from bacteria. These degraded molecules have a molecular of between 272000 and 250000. The aminopeptidase A induces the Polymerization of fibrinogen into ordered structures, the period being 8 nm, when the ionic strength (I) is between 0.1 and 0.2. Fibrinogen modified by the aminopeptidase B precipitates at 4°C (0.075 < I < 0.2)into fibre with a major period of 45 nm. The action of thrombin on these modified fibrinogen molecules at I = 0.3 gives fibres each with two minor striations, whose distribution was however different. These structures were totally different from those of fibrin fibres with its typical major period of 23 nm and its three minor striations. The analysis of the polypeptide chains, the N-terminal-acids and the amino-acids composition of these degraded fibrinogen molecules enables us to differentiate the respective rolesof the polymerization sites in the N and C terminal parts of the Act and Bβ chains.

Therefore, according to our hypothesis the fibre structures obtained from fibrinogen depend on the type of the sites which are discovered on fibrinogen by enzymatic splits and by slight conformational changes.