Purification of glycosylated apoprotein of tissue factor from human brain and inhibition of its procoagulant activity by a specific antibody.

The glycosylated component of tissue factor from human brain which totally retained on Concanavalin A-Sepharose was isolated by a four step procedure. The final product (6-7 S) exhibited an apparent molecular weight of approximately 45,000 under reducing conditions on SDS-gels corresponding with procoagulant activity of tissue factor after detergent removal. The optimal ratio of lipid to protein in reconstituting tissue factor activity was 500:1 (w/w) amounting to 240,000 U/mg. Peptidase activity was not detectable in the purified apoprotein or in the relipidated protein. The procoagulant activity of tissue factor was dependent on Factor VII but not on Factors VIII or IX, since in the absence of Factor VII clotting times were significantly prolonged. The activity of the reconstituted tissue factor could be reduced by a factor of 15 upon incubation with an antibody against the purified glycosylated apoprotein that was raised in the rabbit. The IgG-fraction of the antiserum neutralized the procoagulant activity of tissue factor in saline extracts from human brain and placenta in a time- and concentration-dependent manner indicating common antigenic determinants on the cofactor protein from both tissues.