Hemorrhagic toxins

The role of zinc in the enzymes listed in Table 12 is very often that of a strong Lewis acid, in which substrates are coordinated, polarized and hence activated. In other cases, zinc may play a regulatory, structural or template role. Zinc may also have a structural function in other biological molecules, for example in the unwinding and subsequent rewinding of the double-stranded polymers involved in replication and transcriptional processes. There is also evidence for a role for zinc in the stabilization of membranes and cell walls.463 The high concentrations of zinc in certain snake venoms reflect the presence in the venom of proteolytic enzymes and hemorrhagic toxins that all require zinc for activity.464... 

Hite, L.A., Shannon, J.D., Bjamason, J.B., and Fox, J.W. (1992). Sequence of a cDNA clone encoding the zinc metalloproteinase hemorrhagic toxin e from crotalus atrox evidence for signal, zymogen, and disintegrin-like structures. Biochemistry 37 6203-6211. 

Zinc is also found in purified hemorrhagic toxins and proteolytic enzymes from venoms. Fibrinogenase is a proteolytic enzyme which renders fibrinogen unclottable. This has one Zn per molecule of protein. Further examples include a peptidase from the venom of Agkistrodon... 

Metallopeptidases are the most diverse of the catalytic types of proteases and are characterized by the requirement for a divalent metal ion for their activity (Barett, 1995). They include enzymes from a variety of origins sueh as collagenases from higher organisms, hemorrhagic toxins from snake venoms and thermolysins from bacteria (Weaver et al., 1977 Hibbs et al., 1985 Okada et al., 1986 Wilhelm et al., 1987). Based on the specifieity of... 

Hemorrhagic toxin Agkistrodon acutus, I 216 -5 000 Tris, pH 7.0 84Z2... 

Some snake venoms are more toxic than others because the type and amount of toxic components present in their venoms are different. Usually neurotoxins are most powerful. Cardiotoxins, cytotoxins, hemorrhagic toxins, and myotoxins are also highly toxic but less toxic than neurotoxins. 

A large number of hemorrhagic toxins were isolated, and they were found to be zinc containing proteases (Bjarnason and Tu, 1978 Hite et al., 1992). Hemorrhagic toxins cause hemorrhage by direct action on the capillary endothelium after initial dilation of the endoplasmic reticulum. 

Bjamason, J. B., and Tu, A. T. (1978). Hemorrhagic toxins from western diamondback rattlesnake (Crotalus atrox) venoms Isolation and characterization of five toxins and the role of zinc in hemorrhagic toxin e. Biochemistry 17 3395-3404. 

These proteins have high sequence homology to each other and to known hemorrhagic toxins isolated from snake venoms. It is not clear what the structural difference is between the two types of proteases. When the oxidized insulin B or fibrinogen was used as a substrate, it is hydrolyzed by both hemorrhagic and nonhemorrhagic venom proteases (25, 28-30). However, these proteins have different proteolytic activities in vivo. 

However, three hemorrhagic toxins also fall into this category of sequence similarity to atroxase. So a direct comparison of the primary structure of the zinc bnding region does not give any clues as to why there is a difference in proteolytic activities between hemorrhagic and nonhemorrhagic zinc metalloproteinases. 

Huang, Y., Jiang, B., Wang, Y. Z., and Xu, X., 1988, Studies on the distribution of I-labelled hemorrhagic toxin ( I-AaHI) from A. acutus in rabbits and its pharmacokinetic characters. J. Isotope 1(1) 44. Kondo, H., et al., 1960, Studies on the quantitative method for determination of hemorrhagic activity of Habu snake venom. Jap. J. Med. Sci. Biol. 13 43. 

Zhang, J. J., Chen, Z. X., He, Y. Z., and Xu, X., 1984, Effect of calcium on proteolytic activity and conformation of hemorrhagic toxin I from five pace snake (A. acutus) venom. Toxicon 22(6) 931. 

The ESI mass spectrum of a chromatographically purified unknown hemorrhagic toxin" isolated from Agkistrodon acutus is shown in Figure 9a. The observed heterogeneity indicates that the molecule could be a glycoprotein. The measured molecular mass was 22,879 Da. Further investigation for the purification and characterization of the molecule is underway. 

Figure 9. Mass spectra of hemorrhagic toxin from Agkistrodon acutus (A, acquired ESI-mass spectrum B, MALDI-mass spectrum).

All of the above observations indicate that single chained polypeptides such as pre-synaptic neurotoxins, cardiotoxins and the hemorrhagic toxin form molecular aggregates in a specific manner. Conversely, the process seems to be non-specific among pre-synaptic neurotoxins with an a and P chain. The former phenomenon was observed during the ESI... 

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