Multiple Active Forms of Thrombin

Abstract The two major molecular weight classes of thrombin have been resolved chromatographically on sulfoethyl Sephadex. The larger thrombin is a molecule of 39,000 daltons, composed of two disulfide-linked chains of 33,000 and 6,000 daltons. The smaller thrombins have an intact molecular weight of 28,000. At least two molecular species are contained in this class with the proposed disulfide-linked chain structure (a) 18,000 and 10,000 daltons and (b) 14,000, 4,000, and 10,000 daltons. All the thrombins isolated have identical specific activities toward tosyl-l-arginine methyl ester. The clotting specific activity of the larger thrombin is 2,700 NIH units per mg while those of the two smaller thrombins appear to be about 0.50 and 0.25 of this value, respectively. Studies conducted with Parke-Davis topical thrombin and partially purified prothrombin indicate that the smaller thrombins are sequentially produced from the larger thrombin.