Novel Proteinase Inhibitors in Snake Venoms: Distribution, Isolation, and Amino Acid Sequence

Abstract

Hageman factor, contact factor of blood coagulation system, is found only in mammalian blood plasma and is known to act as a trigger of kallikrein-kinin system and coagulation-fibrinolytic system. Previously, we found that Hageman factor activates directly bovine plasma prekallikrein, splitting only a single arginyl bond on a peptide chain bridged by a disulfide linkage [1, 2]. During this study we established a method to prepare highly purified bovine pre-kallikrein [3]. Subsequently, the authors intended to look for an enzyme with Hageman factorlike activity of other sources using the purifiedpre-kallikrein.lt is well known that snake venoms contain protein components which concern to kallikrein-kinin and blood coagulation systems. Thus, we first took snake venoms to find a nonmammalian pre-kallikrein activating Hageman-like enzyme. Unexpectedly, we could not find the activation of pre-kallikrein with snake venoms. Since snake venoms generally contain proteinases, we tested whether or not venom proteinases destroyed the pre-kallikrein or kallikrein molecule. For this purpose, purified bovine Hageman factor was added to an incubation mixture of pre-kallikrein and snake venom. By the addition of bovine Hageman factor to the mixture, the expected kallikrein activity was fully evolved. However, when the venom of Vipera russelli was present in the incubation mixture, kallikrein activity was not evolved even after the addition of Hageman factor. From this result, it was supposed that a kallikrein inhibitor may exist in the venom, and really the inhibitors in it were isolated. Isolated Russell’s viper inhibitors also inhibited trypsin, α-chymotrypsin and plasmin [4].

This work was supported in part by a grant from the Scientific Research Fund of the Ministry of Education of Japan.