LIPID BINDING PROPERTIES OF HIGHLY PURIFIED rDNA FACTOR VIII

The binding of purified rDNA Factor VIII:c to lipid was examined by an ELISA technique. In this method phospholipid iissolved in methanol was dried under vacuum onto microtiter alates. Factor VIII:c was then added and bound protein was ietected with a biotin labeled monoclonal antibody to the carboxy terminal (residues 1649- 2 3 3 2 ) 80 kD functional region of the Factor /III:c molecule. This was followed by strepavidin-peroxidase and substrate addition. Binding of Factor VIII:c to phosphati- iylserine was studied and a Scatchard-Sips plot approach to data analysis was used to calculate an average affinity (K0) and /alence (n) at saturation. The binding constants for rDNA Factor VIII:c binding to phosphatidylserine were determined to be: K_o = 1 × 10¹⁰ M⁻¹, n = 2,900 (moles lipid/moles protein). Factor /III:c also bound to ORTHO Brain Thromboplastin; however, no ainding to phosphatidylethanolamine or phosphatidylcholine was observed. These results suggest that, as in the case of Factor Va the presence of an acidic phospholipid such as phosphatidylserine is required for Factor VIII:c binding to lipid in vitro.