The Activity of Lung Microsomes in Blood Coagulation.

1. Factor VII, essentially free of Factor X but containing traces of prothrombin, and Factor X, very low in Factor VII, have been prepared by a combination of adsorption to and elution from barium sulfate and chromatography on diethylaminoethyl cellulose. 2. The activation of Factor X by lung microsomes is due to contamination of Factor X with Factor VII rather than to a direct attack on the Factor X molecule by lung microsomes. 3. Factor VII, lung microsomes, and calcium react to form a complex which is able to act as enzyme in activating Factor X. Indirect evidence has been obtained indicating the enzymatic activity of the complex is due to activated Factor VII.