The activity of human placenta microsomes and brain particles in blood coagulation.

1. Human placenta microsomes active in blood coagulation have been prepared by a combination of differential centrifugation, density gradient centrifugation, and extraction with butanol-benzene mixtures. Human brain particles have been prepared from acetone-dried brain by extraction with sodium chloride solutions, differential centrifugation, and extraction with butanol-benzene mixtures. 2. Placenta microsomes and brain particles appear to function as enzyme in the development of coagulant activity from the bovine serum fraction. 3. The coagulant activity, which develops in reaction mixtures containing placenta microsomes, calcium, and bovine serum eluate, rapidly disappeared on storage at 4”. In similar reaction mixtures containing purified brain particles, less than one-half of the coagulant activity could be recovered in the sediment after washing with buffer containing calcium, but from 75 to 100% could be recovered in the supematant fluid after washing with ethylenediamhretetraacetate. 4. Purified brain particles bind protein from the bovine serum eluate nonspecifically and. bind activated Factor X, but do not bind nonactivated Factor X.