98 



E. KOCHVA 



It has been suggested that a system that produced active sub- 

 stances with the means of introducing them into the prey probably 

 lay at the foundation of the major radiations of higher snakes 

 (Underwood & Kochva, 1993). This system underwent further 

 evolution in the Atractaspididae (mainly Atractaspis), Viperidae, 

 Elapidae and several lineages of 'Colubridae'. 



Some of the active substances were probably enzymatic in nature 

 and related to enzymes secreted by evolutionarily 'older' glands, 

 such as the pancreas. Indeed, phospholipases found in the venom of 

 Elapidae, for instance, show sequence homology with the enzymes 

 secreted by the mammalian pancreas. Some of the ancestral en- 

 zymes developed into toxins, such as hemorrhagins and neurotoxins, 

 with or without loss of enzymatic activity (Fig. 14; Strydom, 1979; 

 Kochva, 1987). 



Hemorrhagins are found in two families (Viperidae and 

 Atractaspididae); presynaptic neurotoxins in two (Elapidae and 

 Viperidae); and two families each possess a specific and unique 

 group of toxins - postsynaptic neurotoxins in elapids and sarafotoxins 

 in Atractaspis. 



The hemorrhagin found in the venom of Atractaspis is neutral- 

 ised by antibodies against Vipera palaestinae venom (Ovadia, 

 1987) and may thus be related to viperid hemorrhagins, originat- 

 ing from some kind or kinds of protease. The presynaptic and 

 postsynaptic neurotoxins, as well as the cytotoxins and 

 cardiotoxins, apparently originate from phospholipase-like mol- 

 ecules. The enzyme phospholipase A, may be part of the 

 presynaptic neurotoxins and its enzymatic activity may still be 

 essential for its toxicity. The postsynaptic neurotoxins, the 

 cytotoxins and the cardiotoxins apparently underwent major 

 changes including loss of enzymatic activity, chain shortening 

 and gain of neurotoxicity (Strydom, 1979). 



The sarafotoxins are structurally very similar to the endothelins, 

 which are evolutionarily highly conserved, and are found in all 

 vertebrates, as well as in some invertebrate groups. It should be 

 emphasised, however, that the genes of the mammalian endo- 

 thelins were found on three separate chromosomes, whereas the 

 sarafotoxin genes seem to be located on the same chromosome. 

 The organisation of the SRTX genes of both A. engaddensis and 

 A. in. microlepidota and their precursors are also different from 

 those of the endothelins and may have evolved separately 

 (Ducancel et ai, 1993; 1999). 



There is, of course, a great deal of information still missing, but 

 the evolution of the sarafotoxins and of some of the other snake 

 venom toxins and their use in feeding and defense may best be 

 defined as exaptations; these are features that once had different 

 functions but are now used in a new role that enhances the fitness of 

 their bearers (Gould & Vrba, 1982). 



ACKNOWLEDGMENTS. I would like to thank first and foremost Garth 

 Underwood for everything he taught me, and not only in Herpetology, and for 

 a long and fruitful co-operation and warm friendship. I thank the editors of 

 the Bulletin for inviting me to take part in this publication and Avner Bdolah, 

 David Cundall, Alexandra Deufel, Dan Graur, Eyal Nadir, Olivier Rieppel, 

 Ruth Stalnikowicz and Garth Underwood for comments on the manuscript 

 and for sharing with me some of their unpublished findings. The remarks of 

 the referees and the help of the Editor are also highly appreciated. 



I am very much indebted to my co-workers in Israel, South Africa and 

 Japan for their major share in the different disciplines of the Atractaspis 

 research and to the undergraduate and graduate students (listed in the 

 references) and to many more who picked up the sarafotoxin project (with or 

 without endothelin) and developed it into such a broad and deeply interesting 

 field, with still much more to be expected in the future. 



Special thanks are due to Moshe Alexandroni, Lydia Maltz, Omer 

 Markowitz, Naomi Paz, Amikam Shoob and Varda Wexler for help with the 

 illustrations and with the preparation of the manuscript. 



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