To better understand the diverse effects ofvenom, let us examine several of the common components found insnake venoms. Proteolytic enzymes are trypsin like and accountfor much of the digestive reactions of snake venoms. Theseenzymes break the peptide bonds between amino acids and denatureproteins. Arginine ester hyrdolases break carbon-oxygen bondsthat are not neurotransmitter related (neurotransmitter esteraseswill be explained in greater detail later), but rather causebreakup of certain proteins where arginine residues are frequent.Collagenase degrades collagen, which is a major component ofconnective tissue, skin and flexible vascular tissue. This enzymeis found in crotalid and viperid venoms and this explains thenecrosis often seen following viper bites. Phospholipases A and Bdegrade lipids to free fatty acids and can cause damage to thecell membrane causing lysis and apoptosis. Phosphodiesterasesbreak the phosphate bonds that provide the backbone for nucleicacids, thus rendering DNA and RNA useless in the effected cell,eventually causing apoptosis. Acetylcholinesterase is aneurotransmitter esterase that breaks the acetate ester bondfound in acetylcholine. The main site of action is in thesynapse, although some vesicle-contained acetylcholine may bedegraded as well. The end result of this action is an inabilityto enervate smooth muscle and the inability to relax striatedmuscle resulting in spasmodic paralysis and sometimes aconcurrent drop in blood pressure and difficulty breathing. Somevenoms also contain highly competitive antagonists that preventacetylcholine from binding at the postsynaptic membranereceptors, also causing neurotoxic symptoms and often apnea andasphyxiation will result. DNase and Rnase are enzymes thatdegrade DNA and RNA respectively. NAD Nucleotidase degradesnicotinamide, which is an important part of the cellularmetabolism machinery. Cellular respiration is interrupted andcell death may ensue. L-Amino acid oxidase is found in all knownsnake venoms. Procoagulants cause blood coagulation to occur;conversely Anticoagulants prevent blood from clotting. Bothchemicals may be found in the same venom, which is perplexingsince they may antagonize each other. Anticoagulant action ismore frequent and will cause bleeding at the site of envenomationas well as internal bleeding and tissue edema.
Posts
