부산대학교 도서관

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jcz.2006.01.003 Byline: Stephen P. Mackessy, Louise M. Baxter Keywords: Accessory gland; Autolysis; Enzymes; Gland; Mitochondria-rich cell; Parietal cell; pH; Rattlesnake; Stabilization; Toxin; Venom Abstract: A paradoxical task of the venom gland of snakes is the synthesis and storage of an instantly available suite of toxins to immobilize prey and the protection of the snake against its own venom components. Furthermore, autolysis of the venom constituents due to the action of venom metalloproteases is an additional problem, particularly among viperid venoms, which are typically rich in lytic enzymatic proteins. To address questions concerning these problems, the structure of the venom gland was investigated using light microscopy, SEM and TEM. The composition of the venom originating from the intact venom apparatus or from the main venom gland alone was analyzed by electrophoresis, and the pH of freshly expressed venom as well as pH optima of several representative enzymes was evaluated. Results from several species of rattlesnakes demonstrated that the venom gland is structurally complex, particularly in its small rostral portion called the accessory gland, which may be a site of activation of venom components. Secreted venom is stable in extremes of temperature and dilution, and several proximate mechanisms, including pH and endogenous inhibitors, exist which inhibit enzymatic activity of the venom during storage within the venom gland but allow for spontaneous activation upon injection into prey. Whereas acid secretion by the parietal cells activates digestive enzymes in the stomach, within the venom gland acidification inhibits venom enzymes. We propose that the mitochondria-rich cells of the main venom gland, which are morphologically and histochemically very similar to the parietal cells of the mammalian gastric pit, play a central role in the stabilization of the venom by secreting acidic compounds into the venom and maintaining the stored venom at pH 5.4. Hence, our results indicate yet another trophic link between the processes of venom production and of digestion, and demonstrate that the venom glands of snakes may represent an excellent model for the study of protein stability and maintenance of toxic proteins. Author Affiliation: School of Biological Sciences, University of Northern Colorado, 501 20th St., CB 92, Greeley, CO 80639-0017, USA Article History: Received 4 December 2004; Revised 21 November 2005; Accepted 1 January 2006 Article Note: (footnote) [star] This paper is based on the contribution that was presented as part of the symposium "Venom delivery in snakes: the evolution of a unique morphological system" organized by Kenneth V. Kardong and Bruce A. Young at the Seventh International Congress of Vertebrate Morphology (ICVM), Orlando, FL, USA, 27 July-1 August 2004. Bruce A. Young served as a guest editor.