Neutralization of kinin-releasing enzymes of crotalid venoms by monospecific and polyspecific antivenoms

Phosphodiesterase from Daboia russelli russelli venom: purification, partial characterization and inhibition of platelet aggregation

Phosphodiesterases (PDEs) belong to a super-family of enzymes that have multiple roles in the metabolism of extracellular nucleotides and regulation of nucleotide-based intercellular signalling. A PDE from Russell's viper (Daboia russelli russelli) venom (DR-PDE) was purified by gel filtration, ion exchange and affinity chromatographies. Homogeneity of the preparation was verified by SDS-PAGE, SE-HPLC and mass spectrometry. It was free from 5'-nucleotidase, alkaline phosphatase and protease activities. Identity of the enzyme was ensured from partial sequence homology with other PDEs. DR-PDE was inactivated by polyvalent anti-venom serum and metal chelators. The enzyme was partially inhibited by the root extracts of four medicinal plants but remained unaffected by inhibitors of intracellular PDEs. DR-PDE hydrolyses ADP and thus, strongly inhibits ADP-induced platelet aggregation in human platelet rich plasma. This study leads to better understanding of a component of Russell's viper venom that affects homoeostatic system of the victim.

Purification and characterization of cationic chymotrypsin from the pancreas of the Arabian camel (Camelus dromedarius)

This study reports on the purification and characterization of a cationic enzyme with chymotryptic activity from camel pancreas. The enzyme was purified 52-fold in a 48% yield by a three-step chromatographic procedure consisting of anion-exchange, cation-exchange and affinity chromatographies. The purified enzyme was homogeneous on gel isoelectric focusing and on SDS gel electrophoresis. Its isoelectric point was estimated to be 7.3 and its molecular mass was found to be 23,600 Da. The enzyme was identified as a cationic chymotrypsin according to its physiochemical properties, substrate specificity and susceptibility to inhibition. It was active towards esters of aromatic amino acids but much less active towards a leucine ester. In all cases, the k(cat) values of the camel enzyme were less than the corresponding values of bovine chymotrypsin A. It also showed a lower level of kininase activity. Camel chymotrypsin was more susceptible than its bovine equivalent to inhibition by soybean trypsin inhibitor and aprotinin. It showed the same pH optimum as bovine chymotrypsin A for its esterolytic activity, but was more dependent on CaCl2 for long-term stability.

Purification and some properties of camel carboxypeptidase B

A carboxypeptidase B-like enzyme was purified 116-fold with a recovery of activity of 29% from a crude extract of camel pancreas by a four-step procedure consisting of two anion exchange chromatographies in succession, gel filtration and hydrophobic interaction chromatography. The enzyme was homogeneous on SDS and non-denaturing gel electrophoresis and on gel isoelectric focusing. Its molecular mass was found to be 31.5 kDa and its isoelectric point was estimated as 6.1. It was active towards a number of substrates that are cleaved by carboxypeptidases B from other species and was also susceptible to inhibition by inhibitors of such enzymes. The camel enzyme showed a pH optimum of 8.0 and it was seen to be a relatively potent kininase in vitro. The enzyme purified in this study was very similar to carboxypeptidases B isolated from other species in size, charge, substrate specificity and susceptibility to inhibition and thus it can be identified as camel carboxypeptidase B.

Enhancement and inhibition of snake venom phosphodiesterase activity by lysophospholipids

Lysophospholipids are liberated during venomous action. In this study we demonstrated that lysophosphatidyl choline (LPC) of various acyl chains enhances considerably the activity of snake venom phosphodiesterase (PDE). Lysophosphatidic acid (LPA) and its cyclic form (cLPA), on the other hand, were found to inhibit this enzyme in a non-competitive (LPA) or competitive (cLPA) manner. Both of these activities may contribute to the progression and subsidence of the poisoning profile. PDE from cellular origin was not substantially affected by any of the above lysophospholipids.

Inhibition of habutobin activities by habu antivenom

This study investigated whether habu antivenom inhibits the clotting activity of habutobin, a thrombin-like enzyme from Trimeresurus flavoviridis venom. Habu antivenom, which is available as a commercial antibody against the crude venom of T. flavoviridis, has been used to treat envenoming by T. flavoviridis (the habu snake). The present study was undertaken to determine whether habu antivenom inhibits the activities of habutobin, which involve digestion of the A alpha chain and release of fibrinopeptide A (FPA) in rabbit fibrinogen. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that habu antivenom inhibited the habutobin-induced digestion of the A alpha chain in rabbit fibrinogen. The results of FPA measurements using competitive enzyme-linked immunoassay (CELIA) revealed that habu antivenom inhibited the release of FPA from rabbit fibrinogen induced by habutobin. In addition, a correlation was noted between the digestion of the A alpha chain and release of FPA from rabbit fibrinogen. Analysis of the inhibition kinetics of habu antivenom against the habutobin activity yielded a competitive double-reciprocal plot.

Purification and partial characterization of camel anionic chymotrypsin

An anionic chymotrypsin-like enzyme was isolated from a crude extract of camel pancreas by a three-step procedure consisting of anion-exchange chromatography, gel filtration, and hydrophobic interaction chromatography. The purified enzyme was homogeneous on native and SDS gel electrophoresis and on gel isoelectric focusing. Its molecular mass was estimated as 28.5 kDa and its isoelectric point was found to be 4.4. The enzyme differed markedly from bovine chymotrypsin A in its substrate specificity, showing considerably lower values of the specificity constant for its action on tyrosine, tryptophan, and phenylalanine esters. Its pH optimum was found to be 7.8. It showed lower kininase activity and was more susceptible to inhibition by a number of inhibitors than the bovine cationic chymotrypsin. On the other hand, the camel enzyme showed a much greater hydrolytic activity than the bovine enzyme toward a leucine ester. In terms of its size, charge, and substrate specificity the camel enzyme was very similar to anionic chymotrypsins that have been isolated from other species and thus appears to be a camel anionic chymotrypsin.

A survey of kininase, tyrosine esterase, kininogenase and arginine esterase activities in some snake venoms

Kininase (kinin-degrading), tyrosine esterase, kininogenase (kinin-releasing) and arginine esterase activities of various crotalid, viperid and elapid venoms were measured. Wide ranges of those enzymatic activities were recorded for the crotalid and viperid venoms but no activities were detected in the Naja venoms.

Purification by HPLC anion-exchange chromatography and some properties of a kinin-releasing enzyme from the venom of Agkistrodon halys ussuriensis

A kinin-releasing enzyme was isolated from the venom of Agkistrodon halys ussuriensis using a very convenient two-step procedure consisting of HPLC anion-exchange chromatography. The relative molecular mass was estimated as 24,000 by SDS gel electrophoresis and an isoelectric point of pH 3.7 was established by gel isoelectric focusing. The kinin-releasing enzyme resembled a typical tissue kallikrein in the values of such physiochemical parameters, in its thermal stability, in its lack of activity towards fibrinogen and casein, and in its behaviour with potential inhibitors. Thus, the enzyme can be classified as a kallikrein-like enzyme.

Purification of a second kallikrein from bovine pancreas

Two kallikreins were identified in a homogenate of bovine pancreas in terms of their differential elution from an anion-exchange chromatography column. The kallikreins were quantified by their ability to release kinin from a partially purified preparation of bovine kininogen. The second kallikrein, designated kallikrein B, was purified by a three-step procedure following anion-exchange chromatography consisting of affinity chromatography on a benzamidine-agarose resin, gel filtration and hydrophobic interaction chromatography. An overall purification factor of 556-fold was achieved with a 58% recovery of enzymatic activity. The final material was shown to be homogeneous by a number of electrophoretic analyses. The relative molecular mass of pro-kallikrein B was found to be 26,700 by gel filtration and that of kallikrein B to be 26,000 by SDS gel electrophoresis. Gel isoelectric focusing revealed the presence of several isoenzymic forms ranging in isoelectric point from pH 4.05 to 4.35.

Neutralization of kinin-releasing enzymes from viperid venoms by antivenom IgG fragments

The activities of kinin-releasing enzymes in the venoms of Vipera xanthina xanthina, V. lebetina obtusa, V. aspis aspis, V. lebtina schweizeri, V. ammodytes ammodytes and V. berus berus were determined using a specific radioimmunoassay for kinin. The kinin-releasing activities of all the viperid venoms measured in vitro were neutralized, to varying extents, by two commercially available monospecific antivenoms in the form of F(ab')2 (Zagreb) and Fab (TAb) immunoglobin fragments, indicating a high degree of cross-neutralization of those enzymes.