Interaction of prothrombin and its fragments with monolayers containing phosphatidylserine. 1. Binding of prothrombin and its fragment I to phosphatidylserine-containing monolayers

Abstract

The adsorption isotherms of prothrombin and its fragment I on phosphatidylserine monolayers and on mixed monolayers of phosphatidylcholine and phosphatidylserine were determined by measuring surface radioactivity emanating from the tritium-labeled absorbed proteins at 0.1 N NaCl and between 0 and 10 mM Ca2+. The proteins were absorbed from very dilute solutions, about 10 times more than in previous investigations on bilayer vesicles. The binding constants as obtained from the Scatchard plots were between 3 X 10(6) and 3 X 10(8) mol/L, depending on the experimental conditions. These values are between 2 and 50 times larger, respectively, than the binding constants obtained on bilayer vesicles. Prothrombin absorbs appreciably also in the absence of Ca2+. The significance of these results is discussed.

Topology of the binding site of blood‐clotting factors in model membranes

“…However, our results clearly show that the transfer process occurs without calcium and with membranes of physiological composition. This result emphasizes the binding scheme proposed by Lecompte et al [34], in which the factor first binds to the membrane by a calcium-free mechanism and then the factor-phopholipid complex binds to calcium with high affinity. As this Ca2+-independent binding type is PtdSer selective, electrostatic forces between the basic residues of the proteins (arginine and lysine) and the negative charges of the membranes (PO.…”

Electrochemistry of mercury supported phospholipid monolayers and bilayers

“…Adsorption of prothrombin from solution to the phospholipid was based on increases in the monolayer specific capacitance. This data was compared with data obtained on the adsorption of prothrombin on phospholipid monolayers at the air/ water interface using prothrombin labeled with tritium [27]. In the work with the phospholipid layer on Hg [26], the following equation was used to interpret the penetration of the protein into the lipid monolayer:…”

Electrochemical analysis of a phospholipid phase transition

“…It has been established that the transference to mercury of a monolayer of coverage (h = 1) is independent of the fact that there is excess phospholipid on the solution surface [2,11,12]. This excess coverage at the gas-solution interface is not homogeneous and consists of islands of collapsed lipid within a monolayer [19,20]. The transfer ratio from the gas-solution interface to the mercury electrolyte interface is thus always less than one.…”