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American Zoologist 1983 23(2):427-430; doi:10.1093/icb/23.2.427
© 1983 by The Society for Integrative and Comparative Biology
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Venom Toxins: Plausible Evolution from Digestive Enzymes1

ELAZAR KOCHVA2, ORA NAKAR and MICHAEL OVADIA
Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University Tel Aviv 69978, Israel

Some hydrolytic enzymes are common to the pancreas, the mammalian salivary glands and the snake venom glands. Phospholipase A, which is found in elapid and viperid venoms and in the mammalian pancreas, shows 29 common amino acid residues out of 118–125 positions. Presynaptic neurotoxins and other venom toxins are usually composed of 2–3 units or subumts,one of which is a phospholipase. The Vipera palaestinae two-component toxin retains its lethality when the enzyme is replaced by heterologous venom phospholipases, but not by the pig pancreatic enzyme. This toxin is neutralized by a factor found in the blood serum of snakes, which binds to the phospholipase and inhibits its activity. The blood serum of snakes also neutralizes hemorrhagins and inhibits the protease activity of the venom. It is hypothesized that the developing venom glands first produced enzymes that were already secreted by the pancreas and against which inhibitors were present in the blood. These inhibitors facilitated the evolution of enzyme-based toxins by neutralizing any damaging substances that might have escaped from the venom glands.


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