Observations on the Factor V activator present in Russell's viper venom and its action on Factor V

Abstract

The Factor V activator (RVV-V) of Russell's viper venom can cause a 20–26-fold increase in the Factor V activity of bovine and human plasma whereas only a 2–4-fold increase was obtained under similar conditions with bovine serum Factor V activity. On incubation with RVV-V, bovine plasma Factor V underwent a significant change in behavior on Sephadex chromatography, with an apparent change in molecular weight from a value greater than 400 000 to one near 205 000. Bovine serum Factor V, as isolated, had a molecular weight (size) of approximately 230 000 which did not change on treatment with RVV-V. Of considerable interest and potential importance, RVV-V activity was stable to heat treatment at 90–95°C for 15 min, over a pH range from 1 to 7. A control (unheated) sample showed comparable activity values over the same pH range. However, the Factor X activator (RVV-X) was heat labile; moreover, at pH 3.0 and pH 5.0 with no heat treatment RVV-X was almost completely inactivated. These observations are provocative in that they pose again the question of the nature of Factor V in plasma and the activated form in the clotting mechanism. The venom activator provides a useful tool for the study of molecular changes in Factor V as related to biological activity.