Analysis for sites of anticoagulant action of plancinin, a new anticoagulant peptide isolated from the starfish Acanthaster planci, in the blood coagulation cascade.

1. Effects of plancinin, a new anticoagulant peptide, on the human blood coagulation cascade were investigated. 2. Plancinin prolonged both activated partial thromboplastin time and prothrombin time, and it significantly inhibited factor X activation by both intrinsic (factor IXa-factor VIIIa-phospholipids-Ca2+) and extrinsic (factor VIIa-tissue factor-phospholipids-Ca2+) tenase complexes and prothrombin activation by prothrombinase complex (factor Xa-factor Va-phospholipids-Ca2+) to 13.8%, 4.8% and 10.5% of control value, respectively. 3. Results indicate that sites of anticoagulant action of plancinin may be located in activation steps of prothrombin and factor X.