ON VARIOUS PROPERTIES OF THROMBOPLASTIN (AQUEOUS TISSUE EXTRACTS)

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Abstract
Thromboplastin was prepared by macerating brain, lung, or thymus, freed of blood, extracting with 0.85% NaCl, and heating the extract at 60[degree]C. Its activity was quantitatively detd. by mixing 0.1 cc. with 0.1 cc. of pxalated plasma, adding 0.1 cc. of 0.1 [image] CaCl2, and noting the clotting time. Tissue extract possesses the following properties: (1) It produces a minimum clotting time which cannot be further reduced by additional tissue extract, and no appreciable difference in activity is found in preparations made from brain, lung, or thymus of the same animal; (2) it fails to clot purified fibrinogen, or plasma deprived of pro-thrombin by means of aluminum hydroxide; (3) it loses most of its activity when extracted with a lipid solvent, but the extract shows little thromboplastic activity; (4) its activity is diminished but not completely lost when heated to 100[degree]C for 1 hr.; (5) it exhibits selective activity suggesting species specificity. This is most marked in the case of the guinea pig, tissue extracts of which are very active in accelerating the clotting of guinea pig blood, but practically inactive for cat, dog, rabbit or human blood. The relatively less active response of human blood, however, to thromboplastin is due probably to a smaller concentration of prothrombin. The results suggest that thromboplastin is not free cephalin, but more probably a phospho-lipid complex of which the non-lipid component is an equally essential constituent.

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