A Smaller Molecule SK-Reactive Protein (Plasminogen-Proactivator) Derived from the Macromolecule of Human Plasma Fraction I.

The SK-reactive plasminogen-proactivator reported in detail by previous workers assumed a macromolecule protein though still impure. A smaller molecule proactivator highly purified is described in the present paper.

Fraction I of human plasma was chosen as staring material after preliminary studies. The macromolecule obtained by gel filtration had low specific activity of SK-reactive protein (proactivator) but little UK-reactivity, showing constantly a large molecular weight by repeating gel filtration. The successful purification of proactivator was achieved by Lysine-Sepharose affinity chromatography, using as eluant t-AMCHA (fibrinolysis inhibitor) which was found suitable.

The proactivator fraction thus obtained showed the high sensitivity to SK, other proteins being removed satisfactorily and the specific activity being increased extremely. Even a trace of plasminogen was not detected. Molecular weight of the proactivator was found 98,000 by gel filtration.

The results indicate that the smaller molecule proactivator described is a basic entity of SK-reactive proactivator of plasminogen.