Comparison of protease and related enzyme activities in snake venoms.

We identified the presence of a range of proteolytic enzyme types, normally associated with the process of general intracellular protein catabolism in mammalian tissues, in venom samples from several species of snake and from three subspecies of Russell's viper. Although levels of protease activity in venoms were in general substantially lower than corresponding levels in mammalian tissues, activity levels were comparable with several other classes of enzyme normally considered as significant venom components. Based on the protease types and relative levels of activity present in venom samples, we suggest that a possible function of these enzymes (in addition to their generally held function to increase target tissue permeability to other venom components) may be to interfere with the process of neurotransmission in target tissues, via degradation of neurotransmitter/neuromodulatory oligopeptides; this may be particularly the case for proteases such as leucyl aminopeptidase, the activity of which is greater in some venom types than in mammalian tissues. For the purposes of inter- and intra-species taxonomic classification of snakes, we would suggest that determination of a comprehensive venom protease profile may be of considerable value (particularly for subspecies differentiation) either in conjunction with or in place of more conventionally applied techniques such as analytical electrophoresis.