The interactions of factors X and IX with phospholipid

Abstract

The interactions of human factors X and IX with phospholipid were studied with an ELISA system. In the presence of calcium ions, factor X bound to phosphatidylserine with an affinity of 1.56 × 10 10 M −1 and to phosphatidylcholine with an affinity of 5.6 × 10 9 M −1. In the presence of calcium ions, factor IX bound to phosphatidylserine with an affinity of 8.4 × 10 8 M −1 and no binding to phosphatidylcholine was observed. No competition of factors X and IX for phosphatidylserine binding sites was observed.