AUTOPROTHROMBIN C FROM A COMMERCIAL THROMBIN PRODUCT

The isolation of factor V from bovine plasma

1. A technique for the isolation of factor V from bovine plasma is described. 2. Some of the physicochemical properties of the protein have been measured and the amino acid composition has been determined.

Increased plasminogen activator (urokinase) in tissue culture after fibrin deposition

Lysis of fibrin in tissue culture has been shown to be due to plasminogen activator identified immunologically as urokinase. The present study examines fibrinolytic events in culture, particularly mechanisms leading to increased urokinase levels and accelerated fibrinolysis. Deposition of fibrin on cells in culture was followed by a two- to six-fold increase in urokinase in the supernates and rapid disappearance of the fibrin. Investigation of factors that might be responsible for these events (including fibrin, fibrinogen, vasoactive stimuli, and the enzymes thrombin and plasmin) indicated that the enhanced urokinase yields were mediated through plasmin and thrombin. Study of the possible modes of action of thrombin and plasmin indicated that these enzymes are capable of acting on the cells themselves as well as on cell-produced material. The effect on cells was manifested by mitotic activity or, occasionally, cell injury and death. Although these effects influenced urokinase levels, enhanced yields were explained best by the action of enzymes on cellproduced material. Studies with plasmin and thrombin, and also trypsin, indicated that proteolytic enzymes may act in various ways-affect the stability of urokinase, interfere with inhibition of urokinase by naturally occurring inhibitor(s), and induce urokinase activity from inactive material. Plasma and thrombin appeared to act primarily through the latter mechanism. Inactive material, which gave rise to urokinase upon exposure to proteolytic enzymes and which may represent urokinase precursor, was found in cultures of kidney, lung, spleen, and thyroid. Urokinase in such inactive state appears to be readily accessible to activation by enzymes, particularly plasmin and thrombin, thus facilitating removal of fibrin and possibly also providing pathways to excessive fibrinolysis.

The hydrolysis of phenylalanine methyl ester by bovine thrombin

Thrombin, usually regarded as a trypsin-like enzyme capable of hydrolyzing only esters of the amino acids arginine and lysine, was found to hydrolyze certain other amino acid esters which are considered specific chymotrypsin substrates. L-Phenylalanine methyl ester inhibited the activation of purified bovine prothrombin by autoprothrombin C, Ac-globulin, phospholipid, and calcium. It was subsequently shown that thrombin is capable of hydrolyzing L-phenylalanine methyl ester or L-tyrosine ethyl ester. This activity developed simultaneously with fibrogen clotting activity during activation of purified bovine prothrombin in 25% sodium citrate solutions. Moreover, the activity was closely associated with clotting activity on subsequent chromatography on DEAE-cellulose and Amberlite IRC-50 resin columns. All preparations of bovine thrombin, representing a wide range of purity, which have been examined, exhibited this hydrolyzing activity toward L-phenylalanine methyl ester. Further evidence linking this esterase activity with fibrinogen clotting activity was obtained when both activities were inhibited by 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate, an inhibitor of chymotrypsin.

INTERACTION OF BOVINE AUTOPROTHROMBIN C WITH PHOSPHOLIPIDS AND DIVALENT CATIONS

A thromboplastic enzyme, autoprothrombin C, can be complexed to different phospholipids and removed from solution in the form of such complexes. A technique for dissociating these complexes was developed, resulting in the recovery of the thromboplastic enzyme essentially free of phospholipid and in a higher degree of purity. Calcium ions are required for the formation of the complex, but strontium can replace calcium not only as the metal ion in the phospholipid-complexing system, but also as an autoprothrombin C cofactor in a prothrombin activation mixture. Magnesium was not effective in either system. The role of different phospholipids in the complexing phenomenon was studied and compared with the suitability of the same phospholipids as prothrombin-activating cofactors of autoprothrombin C. All phospholipid preparations studied complexed with autoprothrombin C to some degree, but the most efficient complexing agents were found to be asolectin and a commercial phosphatidyl ethanolamine preparation, both materials being among the ones which demonstrated the highest prothrombin conversion activity. Since thrombin was not complexed under the same conditions, autoprothrombin C could be isolated from commercial thrombin preparations also containing autoprothrombin C.