CONVERSION OF PROTHROMBIN TO AUTOPROTHROMBIN II

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Abstract
With thromboplastin, Ac-globulin, and calcium ions, purified prothrombin converts to biothrombin. This derivative of prothrombin is also obtained with purified platelet factor 3, Ac-globulin, calcium ions, and autoprothrombin n. Need for the latter substance by platelet factor 3 is one marked distinction that can be made between thromboplastin and platelet factor 3. Thromboplastin does not require a cofactor such as platelet cofactor I or autoprothrombin II. Ether extracts of dry brain or of purified platelet factor 3 or of whole platelets yield lipid material. The lipids obtained in this manner are active in a modified Biggs and Douglas thromboplastin generation test; but in contrast to the original thromboplastin or purified platelet factor 3 from which they are obtained do not activate purified prothrombin to thrombin. The lipid material is thus distinctly different from thromboplastin or from platelet factor 3. The lipid is also active in the conversion of prothrombin to autoprothrombin II when purified prothrombin is the substrate or when the prothrombin is in the original plasma or whole blood. Extraction of purified platelet factor 3 leaves a protein residue and it is believed that platelet factor 3 is a lipoprotein. The infrared absorption spectrum of the lipid obtained from purified platelet factor 3 shows strong absorption bands. From the general absorption pattern, we infer that the lipid is not a heterogeneous mixture, but most likely a single substance or consists of several that are nearly alike. Platelet factor 3 lipid(s) is most likely a cephalin-like compound.