Targeting of venom phospholipases: The strongly anticoagulant phospholipase A2 from Naja nigricollis venom binds to coagulation factor Xa to inhibit the prothrombinase complex

10.1006/abbi.1999.1345Archives of Biochemistry and Biophysics3691107-113ABBI

An anti-inflammatory protein secreted from the rat seminal vesicle epithelium inhibits the synthesis of platelet-activating factor and the release of arachidonic acid and prostacyclin

Platelet-activating factor (PAF), a 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, is a mediator of inflam¬mation and endotoxic shock produced by a variety of stimulated cells. Since the main biosynthetic pathway of PAF involves acetylation of 1-O-alkyl-sn-glycero-3-phosphocholine (lyso-PAF) generated from 1-O-alkyl-2-acyl-¬sn-glycero-3-phosphocholine by phospholipase A2, we suggest a general physiological role played by steroid-¬induced anti-(phospholipase A2) proteins in the modulation of PAF synthesis. The results of the present study support this hypothesis since an androgen-induced anti-inflammatory protein, SV-IV, secreted from rat seminal vesicles, inhibits PAF synthesis in stimulated polymorphonuclear neutrophils, macrophages and endothelial cells. SV-IV impairs PAF synthesis by inhibiting the activation of phospholipase A2, that also results in the inhibition of arachidonic acid and prostacyclin release, and of acetyl-CoA: lyso-PAF acetyltransf