Physicochemical Studies on Human Plasminogen (Profibrinolysin) and Plasmin (Fibrinolysin)

SUMMARY 1. Preparations of human plasminogen and plasmin have been examined for ultracentrifugal and electrophoretic homo- geneity. The proenzyme contained about 70 to 80 per cent of a single sedimenting component. Preparations of plasmin were qualitatively similar, although some preparations showed an additional slow peak. By electrophoretic examination, the pro- enzyme revealed a double boundary at low pH, but plasmin showed a single peak. 2. The molecular weight for plasminogen was found to be 143,000, based on a sedimentation constant of 4.28 S - 0.41~ and a diffusion constant of 2.92 X low7 cm.2 sec.+. A molecular weight of 108,000 was estimated for glycerol-activated plasmin, based on a sedimentation constant of 3.56 S - 0.74~. The sedi- mentation rates and the probable molecular weights of strepto- kinase-activated and urokinase-activated plasmins are inter- mediate between these values. 3. The molecular asymmetry of plasminogen was indicated as 8, according to the intrinsic viscosity of 0.08; a higher asym- metry, 22, was calculated from the frictional ratio.