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Venom

Venom


It may be tempting to equate the concept of venom with poison, but to do so would be inaccurate. Many plants, for example, are poisonous but present no harm to humans because they have learned not to eat them. By contrast, one can be quite careful on a walk through the southwestern United States or Australian outback and still have an unfortunate accident involving the venom of a snake. In any given year, around 40,000 people die as a result of snakebites. To be more accurate with the definition of venom, therefore, it must be noted that venom is not just a poison, but one that is injected under the skin of the victim.

Snakes are not the only animals that use venom. Spiders, scorpions, bees, and wasps are also venomous animals. The specific venom used by these animals varies not only with its type (spider venom is different from bee venom, for example), but also within a species. Thus, some spiders are venomous but not actually a threat to adult humans, whereas the bite of other spiders is lethal unless treated with appropriate medicines.

The differences in venoms have important medical implications, but there are also similarities among many venoms. Most are rather complicated mixtures of chemicals, each of which plays some role in the action that the venom takes. Many involve some mechanism designed to immobilize the victim and are therefore targeted at nerve cells that control muscles.

Thus, snake venoms typically contain neurotoxins, but they also often include enzymes that promote various hydrolysis reactions. The neurotoxins carry out the task of immobilizing the victim by interrupting the ability

of the nerve cells to stimulate muscle movement. Hydrolysis helps make the tissues of the victim easier for the snake to digest if it is eaten. These hydrolytic enzymes may include molecules capable of breaking down collagen and phospholipids as well as other enzymes.

For many who study the chemistry of venoms, the neurotoxins hold particular interest. One example would be the polypeptide toxin cobrotoxin that was isolated from the Formosan cobra and analyzed in 1965 by Chen-Chung Yang, a distinguished chair professor at Tsing Hua University in Taiwan. The primary structure of this neurotoxin is indicated in Figure 1, along with some components of its secondary structure. There are sixty-two residues in the primary structure and four di-sulfide bonds in the secondary structure. If even one of these di-sulfide bonds is somehow disrupted, the polypeptide is rendered nontoxic. This points to the fact that secondary structure is important even in small polypeptides, not only full-size proteins.

The action of cobrotoxin arises from its ability to bind strongly to the receptors in postsynaptic neurons. In order for one nerve cell to signal a neighbor, it releases neurotransmitters that diffuse across a small gap called the synapse. The nerve on the other side of the synapse (the postsynaptic neuron ) has proteins that are specifically geared to sense the presence of these neurotransmitters. If these receptors are blocked, the signal is not passed on, and the nerve cell function is disrupted. Cobrotoxin is able to disrupt a specific type of receptor that is sensitive to acetylcholine . Once this polypeptide binds to the receptor, it is not released, so the nerve cell loses its ability to signal and the muscles it is supposed to trigger do not function. If the muscle that stops working is the diaphragm, the animal will not be able to breathe and it essentially suffocates. Cobrotoxin is very toxic, with an LD50 of 65 nanograms per kilogram in mice.

see also Globular Protein; Neurotoxin; Proteins; Toxicity.

Thomas A. Holme

Bibliography

Agosta, William (2001). Thieves, Deceivers, and Killers: Tales of Chemistry in Nature.

Princeton, NJ: Princeton University Press.

Bailey, Graham S., ed. (1998). Enzymes from Snake Venom. Fort Collins, CO: Alaken.

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venom

venom or zootoxin, any of a variety of poisonous substances produced by animals. In poisonous snakes, venom is secreted in two poison glands, one on each side of the upper jaw, and enters the fang by a duct. Snake venom is a complex substance, containing various enzymes and toxins. Venoms differ in their effect according to the preponderance in them of hemotoxic, hemolytic, or neurotoxic agents. Hemotoxins perforate the blood vessels, causing hemorrhage, and hemolysins dissolve the red blood cells. The venom of the fer-de-lance is chiefly hemotoxic; that of the rattlesnake, the copperhead, and the moccasin is both hemotoxic and hemolytic. Neurotoxins produce paralysis, often of the nerve centers that control breathing, thus causing a quicker death from suffocation. Cobras, coral snakes, scorpions, and spiders produce neurotoxic venoms. The venom of the gaboon viper is both hemotoxic and neurotoxic. Venoms may also contain agglutinins, which promote coagulation of blood, or anticoagulants, which have the opposite effect. The venoms of various snakes have been used medicinally, according to their specific properties, as painkillers (in arthritis, cancer, and leprosy), antispasmodics (in epilepsy and asthma), and blood coagulants (in hemophilia). The venom of the Russell's viper has been used as a coagulant in tonsillectomies and for bleeding gums. The effect of any snakebite necessarily depends on the quantity and kind of toxin it contains, as well as on the resistance of the victim. Immune serum against snake venom, or antivenin, can be prepared by repeatedly injecting sublethal doses of venom into an animal such as the horse. The immune serum thereby produced in the animal can be extracted and used to treat snakebite victims. Poisons are produced by animal species of every phylum; examples include the poison in the rounded warts of the skin of toads, the venoms of spiders, scorpions, bees, and other arthropods, and the poison of jellyfish and other coelenterates. See also toxin.

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venom

ven·om / ˈvenəm/ • n. poisonous fluid secreted by animals such as snakes and scorpions and typically injected into prey or aggressors by biting or stinging. ∎ fig. extreme malice and bitterness shown in someone's attitudes, speech, or actions: his voice was full of venom. ORIGIN: Middle English: from Old French venim, variant of venin, from an alteration of Latin venenum ‘poison.’

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venomous

ven·om·ous / ˈvenəməs/ • adj. (of animals, esp. snakes, or their parts) secreting venom; capable of injecting venom by means of a bite or sting. ∎ fig. (of a person or their behavior) full of malice or spite: she replied with a venomous glance. DERIVATIVES: ven·om·ous·ly adv.ven·om·ous·ness n.

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venom

venom poison, lit. and fig. XIII. ME. venim — OF. venim, (also mod.) vénin :- Rom. *venīmen, alt. of L. venēnum potion, drug, poison.
So venomous †pernicious XIII; poisonous XIV. — (O)F. venimeux.

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"venom." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 18 Aug. 2017 <http://www.encyclopedia.com>.

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venom

venom from the Latin venenem, meaning poison. Refers to the poisonous fluid secreted by some snakes and spiders and injected into the victim by a bite or sting.

Alan W. Cuthbert


See poisons.

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venom

venom (ven-ŏm) n. the poisonous material produced by snakes, scorpions, etc. Some venoms produce no more than local pain and swelling; others can prove lethal.

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venom

venom •minimum • maximum • optimum •chrysanthemum, helianthemum •cardamom • Pergamum • sesamum •per annum • magnum • damnum •Arnhem, Barnum •envenom, venom •interregnum • Cheltenham • arcanum •duodenum, plenum •platinum • antirrhinum • Bonham •summum bonum • Puttnam •ladanum • molybdenum • laudanum •origanum, polygonum •organum • tympanum •laburnum, sternum •gingham • Gillingham • Birmingham •Cunningham • Walsingham •Nottingham • wampum • carom •Abram • panjandrum • tantrum •angstrom • alarum • candelabrum •plectrum, spectrum •arum, harem, harum-scarum, Sarum •sacrum, simulacrum •maelstrom • cerebrum • pyrethrum •Ingram •sistrum, Tristram •Hiram •grogram, pogrom •nostrum, rostrum •cockalorum, decorum, forum, jorum, Karakoram, Karakorum, Mizoram, pons asinorum, quorum •wolfram • fulcrum • Durham •conundrum • buckram • lustrum •serum, theorem •labarum • marjoram • pittosporum •Rotherham • Bertram

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venomous

venomous •Lammas • Cadmus • Las Palmas •chiasmus, Erasmus •Nostradamus •famous, ignoramus, Seamus, shamus •Polyphemus, Remus •grimace • Michaelmas •Christmas, isthmus •litmus •animus, equanimous, magnanimous, pusillanimous, unanimous •anonymous, eponymous, Hieronymus, pseudonymous, synonymous •Septimus •Mimas, primus, thymus, timeous •Thomas •enormous, ginormous •brumous, hummus, humous, humus, spumous, strumous •blasphemous •bigamous, polygamous, trigamous •endogamous, monogamous •calamus, hypothalamus, thalamus •venomous •autonomous, bonhomous, heteronomous •Pyramus •dichotomous, hippopotamus, trichotomous •Thermos

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