[Modification of fibrin assembly as a method for studying the mechanism of this process]

A study of monomeric fibrin assembly--the process at which the ordered fibres are formed and at the definite moment there arises an elastic three-dimension net (coagulation occurs) made it possible to establish the following. Fibrinogen and high-molecular fragment D formed in fibrinogen enzymatic hydrolysis inhibit the assembly and prevent from creating the regular morphological structure of the fibres. This effect is determined by the presence in fibrinogen and fragment D. of a part of those specific binding centres by means of which the fibrin molecules recognize each other and realize the assemply. The early but not late stages of the assembly are sensitive to fibrinogen and fragment D. This fact evidences for difference in the mechanisms acting at these stages of the process. A moderate increase in the ionic strength prolongs sharply the clotting time of fibrin monomer, that is connected with both retardation in the assembly and prolongation of the pathway in the transformation itself. Transition from the high ionic strength to the low one produces the opposite effect--acceleration in the assembly and shortening of the pathway. For the subsequently appearing intermediate products of the assembly there exists a threshold at which a slow stage of growth and ordering is replaced by the fast terminal reaction of fibre formation. The threshold height is not constant, it depends on the conditions under which the assembly proceeds. The hypothetic explanations of the obtained results are advanced.