The influence of the surface charge of phospholipids on the activity of the prothrombin converting complex

Abstract

<h2>Abstract</h2> During blood coagulation factor V is converted into its activated form, factor Va, by the action of thrombin. In the presence of Ca⁺⁺-ions, phospholipids, factor Xa and factor Va, a complex is formed, prothrombinase, which converts prothrombin into thrombin. The influence of the surface charge of various phospholipid micelles on the formation of this complex was studied. As phospholipids purified phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidic acid (PA), phosphatidylinositin (PI), phosphatidylcholine (PC) and mixed micelles of some of these phospholipids were used. The experiments revealed that after the addition of phospholipids to factors Va, Xa, II and Ca⁺⁺-ions two reaction phases could be distinguished. During the first phase a fall of factor Va activity occurred, which was faster as the negative charge of the micelles increased. The presence of factors II and Xa was not required for this reaction. This fall in activity suggests that Ca⁺⁺-ions are needed for the stability of factor Va. During the second phase maximal reduction rate of factor Va activity, accompanied by maximal thrombin generation from prothrombin, occurred only in the case of an optimal negative surface charge of the phospholipid micelles. The presence of factors II and Xa was essential for this reaction. The second reaction phase probably implies consumption of factor Va in favour of thrombin generation.