Variability of the anticoagulant fraction of incubated fibrinogen

The spontaneous breakdown of human fibrinogen or the lysis of Laki's fibrinogen by purified human fibrinolysin and streptokinase involves at least two different reactions. Clottability by thrombin and precipitability at 25% ammonium sulfate saturation are gradually lost but although clottability disappears completely at a fairly early stage, precipitability is still retained by 4–12% of the original protein even during advanced stages. Both the amount and the antithrombic activity of the anticoagulant fraction of incubated fibrinogen (AFIF) produced vary throughout fibrinogenolysis. The changing quality of AFIF is further evidenced by changes in the electrophoretic patterns which indicate variations in concentration, mobility, and number of components. Strip electrophoresis of fractions isolated by continuous-flow paper electrophoresis showed the presence of two components in the largest fraction but only of a single one of different mobility in a second, smaller fraction. The last finding makes it unlikely that the antithrombic effect exerted by the latter fraction could be due to contamination by components of the former.

INACTIVATION OF PURIFIED AUTOPROTHROMBIN I WITH ANTITHROMBIN

Autoprothrombin Ic was obtained by activating prothrombin preparations with autoprothrombin C. Autoprothrombin Ip was obtained by activating prothrombin with the use of calcium ions and purified platelet factor 3. Both of these prothrombin derivatives were found to be inactivated by plasma and serum. Autoprothrombin Ic was studied most extensively and was found to be inactivated by purified antithrombin. When antithrombin was first combined to capacity with purified thrombin the power to neutralize autoprothrombin I was almost eliminated. Autoprothrombin II was not destroyed by antithrombin and was found in serum as the main procoagulant. Most likely it is not in plasma. Autoprothrombin Ic, autoprothrombin Ip, autoprothrombin C, and thrombin all have reactive groups that combine with antithrombin. The activity in 1 mg of purified autoprothrombin Ic was neutralized by 50 ml plasma. One milligram of autoprothrombin C was neutralized by 5 ml plasma, and 7 ml plasma was sufficient to neutralize 1 mg of thrombin. Antithrombin IV is regarded as a kinetic effect and not as a substance. From a review of the literature it is concluded that there is no adequate evidence for appreciable quantities of factor VII in serum, or that it occurs in plasma independent of prothrombin.

THE ACTION OF A PROTEOLYTIC ENZYME FROM ASPERGILLUS ORYZAE ON COMPONENTS OF THE BLOOD CLOTTING SYSTEM

CA.7, a highly purified proteolytic enzyme from Aspergillus oryzae, acts on a number of the coagulation factors. In low concentrations, immediate action is to decrease the recalcified clotting time. The evidence, as furnished by experiments on a prothrombin fraction, is that it does this by converting prothrombin to thrombin. In this regard its action is similar to that of thromboplastin. During incubation, especially with increasing concentrations, it destroys prothrombin and fibrinogen, and plasma becomes incoagulable. It destroys normal plasma antithrombin but, paradoxically, generates a thrombin–fibrinogen inhibiting activity by its proteolytic action on fibrinogen in plasma.

NEUTRALIZATION OF AUTOPROTHROMBIN C ACTIVITY WITH ANTITHROMBIN

A concentrate of antithrombin was made from bovine plasma. When examined with an analytical ultracentrifuge it was found to contain a main component and a small amount of more rapidly sedimentating material. For the main component [Formula: see text] was 4.01 S. The antithrombin concentrate destroyed the activity of purified autoprothrombin C, and most likely antithrombin and antiautoprothrombin C are one and the same substance. The antithrombin preparation was limited in its capacity to destroy autoprothrombin C activity, and equilibrium conditions were reached in 3 to 4 hours. At equilibrium the quantity of autoprothrombin C destroyed was proportional to the antithrombin added to an "excess" of autoprothrombin C. The last traces of the latter activity could only be neutralized with difficulty. Under optimum conditions 1 ml of plasma can neutralize the autoprothrombin C that might generate from 27 ml of plasma. About 0.83 ml of oxalated bovine plasma can neutralize the activity in 1 mg of purified autoprothrombin C.

ISOLATION AND PROPERTIES OF ANTICOAGULANTS FROM FIBRINOLYSED AND HUMAN HEART-PUMP PLASMAS

A method is described for the isolation from plasma of breakdown products of fibrinogen having anticoagulant properties. Intact fibrinogen is removed by addition of ether (to 11% by volume) and the anticoagulant is then precipitated by 25% ammonium sulphate saturation of the supernatant. With this method, anticoagulant fractions from in vitro lysed human plasma, human heart-pump plasma, and in vivo lysed rabbit plasma have been isolated. The electrophoretic patterns of the fractions isolated from lysed human plasma and heart-pump plasma were similar to that of AFIF and consisted of two main components, one exhibiting the same mobility as intact fibrinogen and another being more electronegative. Both fractions were found to possess antithrombin activity. The fraction isolated from plasma of rabbits injected with fibrinolysin was separated into three main components. The antithrombin activity of lysed plasmas, human and rabbit, increased with increasing pH values, while that of the heart-pump plasma, after an initial increase, seemed to decrease above pH 7.8. In further similarity to AFIF, all fractions counteracted the procoagulant effect of protamine sulphate, but only the fraction isolated from adsorbed lysed plasma showed an antithromboplastic effect as well. Measurement of optical densities at 600 mμ of mixtures of fibrinogen and the anticoagulants, after addition of thrombin, indicated that all anticoagulants: (a) delayed the beginning of polymerization; and (b) decreased the opacity of the resulting clot.No correlation could be established between the variable levels of antithrombin activity of the fraction isolated from the heart-pump plasma and the severity of the condition of the patient.