Composition of scorpion venom
Composition of scorpion venom
Many holds the impression that scorpion venom is one single compound. Few things can be further from truth. An average scorpion's venom contains numerous toxins, biogenic amines, enzymes, salts, unidentified substances and water.
I have divided the composition of toxins into two main groups; the Buthidae and the Chactoids (including Scorpionidae, Vaejovidae, Ischnuridae, Diplocentridae, Iuridae, Superstitionidae.)
Buthidae
In a 1984 publication, 80 toxins has been found. With scientific advances at our present rate, many more should have been discovered. Most of these toxins have low histidine and phenylalanine, no methionine and are highly hydrophobic and basic. There are numerous cysteine residues giving rise to stable di-sulphide bonds in the tertiary structure of almost all buthoid toxins.
At least 15 toxins are found in venom of Centruroides spp and at least 22 in
Mesobuthus epeus. In Androctonus australis which is extensively studied by
Zlotkin et al., he discovered three groups of toxins each specific to 1) Mammal (toxin I
and II) 2) Crustacean 3) Insects.
In another study by Gomez et al. 1996, the effects of some Tityustoxin on calcium and
sodium ion channels is analysed.
Another way of older classification is in dividing the toxin's effect on sodium(Na) ion
channels.
Class I: inactivates the Na channels and prolongs the action potential of nerve
Class II: activates the Na channels and cause spontaneous and repetitive excitation
of nerve
Class III: Reduces the ionic exchange of sodium and potassium between the extracellular
(ECF) and intracellular fluid (ICF)
ToxinVar3 of Centruroides exilicauda belongs to Class I.
It is, however, found that charybotoxin of Leiurus quinquestriatus and noxiustoxin of Centruroides noxius acts primarily on the potassium channels thereby making the above classification obsolete.
To simplify things, toxins are known to affect sodium ion, potassium ion and calcium ion channels with regards to electrolyte balance. Disturbance to the electrolyte balance can affect the following.
Recently a non-toxic antigenic compound, TsNTP, has been isolated from venom of Tityus serrulatus by Ferreira et al. We see here that many more unidentified non-toxic substances in venom may await our discovery. These may yet prove useful for development of anti venom.
In chactids and vaejovids, the cocktail of other substances is more well studied. The same cannot be said of their neurotoxins as they are not considered as medically important as the Buthidae.
5 hydroxy-tryptamine (5-HT) also known as serotonin is known to cause strong vasoconstriction and pain. The venom of chactoids are also known to affect the eicosanoids pathway which includes different classes of prostaglandins, leukotrienes and serotonin.
In Scorpionidae, there's pronounced hemolytic enzymic (break down blood)activity and this may aid it's digestion. Phospholipase A, found also in snakes (as PL A2), is isolated from Heterometrus scaber. The other contents are acid phosphatase, ribonuclease, acetylcholinesterase and some proteolytic enzymes. However, there is a peculiar absence of DNAse activity in the venom studied thus far.
I applaud your effort if you read till here. I went through stacks of notes, books and articles and combined my pharmacology, biochemistry, pathology, physiology, microbiology and anatomy knowledge to make head and tails of the articles. Simplification is even a bigger headache as I must make it simple and yet not lose the essense of the original article. Alas, a short article like above took me 5 hours to compile and 'simplify'. Many would still think it's just loads of jargons. Humour me, say you understand. ;-)