Medium molecular weight factor X activating enzyme from Vipera berus berus venom.

Vipera berus berus venom contains several factor X activating enzymes. One of them (VBFXAE) was separated by gel-filtration on Sephadex G-100 superfine and on a bacitracin-agarose column. The enzyme is a single-chain glycoprotein with mol. wt 38,000. The enzyme has several molecular forms with pI 3.5-4.5. After neuraminidase treatment the enzyme has pI 4.5. VBFXAE contains 2 Ca per mole. The activator is inactive on synthetic substrates, on casein, prothrombin, and fibrinogen, and appears to act specifically on factor X. The activator also weakly hydrolyses the insulin B-chain at the positions Ala14-Leu15 and Tyr16-Leu17. The cleavage of the insulin B-chain is inhibited by EDTA, suggesting the metalloproteinase nature of the enzyme.