Abstract

We have previously shown that an ideal amphipathic helical peptide of K7L15 composition (IAP) accelerates factor IXa-mediated factor X turnover and factor Xamediated prothrombin turnover in a phospholipid free system (

Biochem J.
,
2008
,
412
:
545
). Under these conditions, IAP behaves as a phospholipid membrane allowing coagulation factors to bind and exert their actions. However, when IAP is used with in vitro assays that employ phospholipids such as an active partial thromboplastin time (aPTT), IAP paradoxically behaves as an anticoagulant by prolonging clotting times. We hypothesize that this anticoagulant effect occurs by blocking binding sites for coagulation factors on phospholipids membranes. To test this hypothesis, we employed three phopholipid-dependant coagulation assays, the aPTT, dilute PT and dilute RVV, with both low and high concentrations of phospholipids. We show that these coagulation times are prolonged by IAP in a concentration dependent manner and that this prolongation is abrogated by adding excess phospholipid, demonstrating phospholpid dependence for this inhibition. In purified tenase and prothrombinase assays, in the presence of phospholipids, IAP inhibits substrate turnover consistent with our hypothesis. To show direct binding between IAP and phospholipids, we conducted fluorescence spectroscopy experiments and show direct binding between IAP and phospholipid membranes. In summary, the above data demonstrate that IAP acts as an anticoagulant by blocking the interaction of coagulation factors with phospholipids membranes.

Disclosures: No relevant conflicts of interest to declare.

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