Characteristics and lipid requirements of coagulant proteins extracted from lung and brain: the specificity of the protein component of tissue factor

Abstract

Soluble proteins were prepared from bovine lung and brain which, when combined with phospholipids, had the biological characteristics of tissue factor. The proteins were solubilized from delipidated (heptane; butanol-extracted) acetone powders with deoxycholate, and precipitated by (NH₄)₂SO₄ (30-60% saturation). These soluble proteins, which contained less than 1% phospholipid, were essentially inert in an assay for tissue factor. When they were recombined with phospholipids, however, activity increased by a factor of 500-1000. Phosphatidylethanolamine was the most active specific phospholipid, followed by phosphatidylcholine. Phosphatidylserine was inert. Mixed phospholipids were from two to four times more active than phosphatidylethanolamine. Maximum activity was obtained at phospholipid to protein ratios of 1.5:1 (wt/wt), and when relipidation was performed in deoxycholate followed by dialysis against 0.05 M imidazole-0.375 M NaCl, pH 7.2. The proteins were characterized by gel filtration on Sephadex G-200; the activity eluted as a single peak with an apparent mol wt of 425,000. The brain and lung activities were recovered from chromatography on triethyl-aminoethyl-cellulose as single peaks, although the salt concentration required for elution was different for each protein. This suggests that within each organ there is one tissue factor-protein, but there may be molecular differences between brain and lung tissue factor. Alternatively, the chromatographic differences may simply reflect charge differences imparted to the proteins by residual lipids.