The Activation of Factor X by Extracts of Rabbit Brain

Thromboplastic preparations were obtained from rabbit brain. The dataindicate that standard acetone-dried reagent functions by activating factorX, with factor VII as an accelerator. When crude tissue reagent was fractionated by butanol treatment and saline extraction, a water-soluble materialwas obtained which similarly activated factor X. In each case, a source ofphosphatide was necessary for activated factor X to yield full clotting activity;this phosphatide was provided in the crude tissue reagent but it was lacking in the water-soluble extract.

The extract was further purified and characterized. It appears to be aprotein and it evidently activates factor X enzymatically. The data thusindicate that brain thrombloplastin contains two separable clotting activities:one of these activates factor X, the other supplies phosphatide.

Submitted on July 21, 1963 Accepted on November 16, 1963