title: Phospholipid-binding properties of bovine factor V and factor Va.
abstract: Factor V and factor Va binding to single bilayer phospholipid vesicles was investigated by light-scattering intensity measurements. This technique allows the measurement of free and phospholipid-bound protein concentrations from which equilibrium constants can be obtained. As controls, the Ca2+-dependent phospholipid binding of prothrombin and factor X were also studied. The average values obtained for the dissociation constants (Kd) and lipid to protein ratio at saturation, moles/mole (n), for prothrombin (Kd = 2.3 X 10(-6) M, n = 104) and factor X (Kd = 2.5 X 10(-6) M, n = 46) binding to vesicles containing 25% Folch fraction III and 75% phosphatidylcholine in the presence of 2 mM Ca2+ were in agreement with those reported in the literature. The average factor V and factor Va values for the dissociation constants and lipid to protein ratio at saturation (moles/mole) were Kd = 7.2 X 10(-8) M and n = 270 for factor V and Kd = 4.4 X 10(-7) M and n = 76 for factor Va. In contrast to prothrombin and factor X, factor V and factor Va demonstrated Ca2+-independent lipid binding. In addition, the number of factor V and factor Va molecules bound per vesicle was found to be dependent both on the phosphatidylserine content of the vesicle and the ionic strength of the buffer.
mesh_terms: D000818:Animals; D002118:Calcium; D002417:Cattle; D005165:Factor V; D005170:Factor X; D007700:Kinetics; D008027:Light; D008970:Molecular Weight; D010743:Phospholipids; D011485:Protein Binding; D011516:Prothrombin; D012542:Scattering, Radiation
chemical_list: D010743:Phospholipids; D005165:Factor V; D011516:Prothrombin; D005170:Factor X; D002118:Calcium