Enzymes of snake venoms

Snakes' venom is a mixture of biologically active substances, containing proteins and peptides. A number of these proteins interact with haemostasis system components. Activators and inhibitors affecting blood coagulation and fibrinolysis systems are of special interest. Venom components can be classified into three main groups, such as procoagulants, anticoagulants and fibrinolytic enzymes according to their action. This review is focused on enzymes from Agkistrodon halys halys venom. They are thrombine-like enzyme, named Ancystron-H, flbrinogenolytic enzyme, protein C activator and platelet aggregation inhibitor. Ancystron-H is used for determination of fibrinogen level in blood plasma of patients undergoing heparin treatment and blood coagulation inhibitors accumulation. The fibrinogenolytic enzyme can be used as the instrument for protein-protein interactions in fibrinogen-fibrin system. The protein C activator is used for protein C level determination in blood plasma with different pathologies. Functions of the platelet aggregation inhibitor, belonging to disintegrins group, can be used for development of antithrombotic preparations. Information about the use of snake venoms in science and medicine is presented.     

Electrophoretic analysis of snake venoms

Electrophoretic analyses were conducted on snake venoms from 21 species representing Elapidae, Crotalidae and Viperidae. Denatured and native venoms were analyzed by polyacrylamide gel electrophoretic (PAGE) methods with sodium dodecyl sulfate (SDS) and without SDS. Both SDS-PAGE and PAGE profiles of venoms from different snake species indicate that some proteins and polypeptide components of these venoms have common electrophoretic characteristics suggesting a genetic relationship. Conversely, the electropherograms also showed the characteristic protein and polypeptide profiles that could differentiate one snake species from another. Therefore, both SDS-PAGE and PAGE profiles suggest that proteins and polypeptides with similar characteristics abound among subspecies or related species, although each venom has a unique profile that differentiates one species from the other.     

Amino acid sequence of VlF: identification in the C-terminal domain of residues common to non-hemorrhagic metalloproteinases from snake venoms

The complete amino acid sequence of a non-hemorrhagic fibrino(geno)lytic enzyme (VlF) isolated from Vipera lebetina venom has been determined. VlF was subjected to separate enzymatic and chemical digestions. Resulting fragments were purified by RP-HPLC and subjected for sequencing by automated Edman degradation. The amino terminus of VlF was determined by mass spectrometry. VlF was shown to be composed of 202 residues having a relative molecular mass of 22,826 Da and containing a zinc-binding site and a catalytically active residue. It displayed significant sequence similarities with many other mature metalloproteinases reported from snake venoms. Sequence comparison of hemorrhagic and non-hemorrhagic mature metalloproteinases revealed the presence at the C-terminal part of the enzymes of two residues common to only hemorrhagic metalloproteinases and two others shared by only non-hemorrhagic ones.     

Facilitation of transmitter release by neurotoxins from snake venoms

Toxins C13S1C3 and C13S2C3 from green mamba venom (Dendroaspis angusticeps) acted like dendrotoxin to increase acetylcholine release in response to nerve stimulation in the chick biventer cervicis preparation. Proteins B and E from black mamba venom (Dendroaspis polylepis) had no prejunctional facilitatory activity. All four proteins are trypsin inhibitor homologues. Binding of a prejunctional facilitatory toxin (Polylepis toxin I) to motor nerves was rapid and did not require the presence of Ca2+ or nerve stimulation. Binding was not prevented by protease inhibitors that lacked facilitatory actions. Prejunctional facilitatory toxins also augmented transmitter release in the chick oesophagus and the mouse vas deferens preparations. The effects were rapid in onset and could wane spontaneously. 125I-labelled dendrotoxin bound specifically to rat brain synaptosomes with a KD of about 3 nM. Binding was prevented by native dendrotoxin but not by beta-bungarotoxin or atropine. It is concluded that prejunctional facilitatory toxins affect transmitter release at many types of nerve endings in addition to motor nerve terminals. From consideration of the structures of active and inactive molecules, it is thought that binding of the active toxins may involve several exposed lysine residues.     

Amino acid sequences of cytotoxin-like basic proteins derived from cobra venoms

Amino acid sequences of cytotoxin-like basic proteins (CLBPs), purified from the venoms of Formosan cobra (Naja naja atra) and Indian cobra (Naja naja), were reinvestigated. The determined sequences differed from those reported previously by Takechi et al. [(1985) Biochem. Int. 11, 795-802; (1987) Biochem. Int. 14, 145-152]. The sequence of CLBPs at residues 25-30 was found to be hydrophilic as compared with those of cytotoxins. The difference in the hydrophobicity of this region might be responsible for the difference in their cytotoxic activities.     

蛇毒类激肽释放酶的研究进展

蛇毒丝氨酸蛋白酶是蛇毒中一类丰富的蛋白水解酶,具有重要的临床应用价值。其中一种丝氨酸蛋白酶一类激肽释放酶,作用于激肽原释放激肽,引起血管舒张,改善微循环,从而逐渐受到关注。对蛇毒中类激肽释放酶的分布、分离制备、生化性质、结构研究和药效研究等方面进行了综述,同时指出了目前存在的问题及今后的发展方向,以期为进一步的基础研究提供理论基础。