чyвcтвитeльнocть к cпeцифичecким ингибитopaм paннич и пoзднич cтaдии caмocбopки фибpинa

Fibrinogen and its degradation products - specific inhibitors of fibrin polymerization, were added to dissolved fibrin prior to or during polymerization. Inhibitor additions were timed so as to cover the whole period of polymerization up to the outset of clotting. The results clearly demonstrated that when the addition delay was gradually increased the inhibitory effect decreased much sharper than expected, i.e. the actual retardation of clotting proved less than the value calculated on the admission that all the polymerization stages were equally susceptible. (In the Table I figures represent seconds of clotting retardation; column 3 - found, column 4 - calculated). At the latest polymerization stages the inhibitory effect vanished altogether. Both of the manifestations of the inhibitory activity, prolonged clotting time and deminished gel turbidity, subsided in parallel as the moment of inhibitor introduction was moving towards the moment of clotting. FIG. 1 shows turbidity increase during the clotting of two fibrin monomer preparations one of which (A) had been preliminarily activated (14); the upper curve corresponds to the inhibitor-free controle, the lowest curve - to the sample containing the inhibitor from the very beginning of the polymerization, the intermediate curve - a sample to which the inhibitor was added with a delay equal to 50% of the controle clotting time. Fibrinogen labelled with fluoresceineisothiocyanate was found to be incorporated into fibrin clot more readily at early polymerization stages. Electron microscopic examination revealed striking structural defects in fibrin fibres whose formation was influenced by the inhibitor throughout the polymerization process. If added at later stages the inhibitor caused little or no structural damage (FIG. 2–5). Thus, the susceptibility to specific inhibitors disappeares to a great extent during the early polymerization stages. In contrast with the specific inhibitors other inhibitors, like urea or hexamethylene glycol, are fully effective even if applied just before clotting would began. This striking difference suggest that the early and late polymerization stages differ from each other in respect to molecular mechanisms involved.     

Кoличecтвeннoe oпpeдeлeниe cпeцифичecкич ингибитopoв пoлимepизaции фибpинa. Eдиницы тopмoзящeй aктивнocти

Fibrinogen and its degradation products are to be regarded as specific inhibitors of fibrin polymerization because of the protein-protein recognizing manner of their action. Some effects of specific inhibitors, e.g. prolongation of clotting time are easily measurable, yet, a proper quantitative presentation of the inhibitory activity is a separate problem requiring consideration. No series of direct measurements of inhibitory effects can adequately reflect the relative activities of inhibitors in question as the inhibitor concentration - effect dependence is non-linear. In Figure 1 curves for fibrinogen and fragment D are shown. Ordinate - relative prolongation of pure fibrin monomer clotting, abscissa - inhibitor concentration. The curves suggest some cooperativity in fibrin-inhibitor interactions. Dotted lines indicate a striking change in relative activity of the two inhibitors due to altering the concentration chosen for the activity-comparison test. Thus, the mere values of the inhibitory effects can give hardly more than semi-quantitative hints on the intrinsic inhibitory activities. To gain true values we made resort to the estimated weight quantities of inhibitors producing the same effect. As these quantities are obviously inversely proportional to the specific activity values of the respective inhibitors they immediately provide the information wanted. An arbitrary standard was chosen: 10-fold retardation of fibrin monomer clotting at definite medium conditions. So it became possible to express activities of specific inhibitors in terms of special units. In mixtures of inhibitors the overall activity (the total amount of activity units) was found equal or near to the sum of unit contents of all the components present. Consequently, the behaviour of components is virtually additive (Tables 2 and 3). This additivity means that the effects of individual components enhance each other in the same co-operative manner as the effectiveness of a single inhibitor is raised by its concentration increase (Figure 1). The arithmetical sum of separately exerted effects of components generally proved far below the actual effect of the corresponding mixture. This difference, as expected theoretically, was maximal if the components were represented in equivalent amounts, and it was less for a two-component system than for a three-component one. These results warrant the adequacy of the new method. Following determinations were carried out with this method. In fibrinogen solutions subjected to tryptic hydrolysis the activity unit content increased by about 300 per cent under optimal conditions, i.e. in the presence of Ca²⁺ and at 1:2250 trypsin-fibrinogen weight ratio. Specific activities of fibrinogen and purified fragment D were found to amount to 1.4 and 10.9 units per mg respectively. Throughout our work on fragment D isolation from tryptic fibrinogen digests activity yields were determined to check the procedure under trial.