Isolation and characterization of a lethal myotoxic phospholipase A from the venom of the common sea snake Enhydrina schistosa causing myoglobinuria in mice

Myotoxic phospholipases A from snake venom, Pseudechis colletti, producing myoglobinuria in mice

2 proteins producing myoglobinuria in mice were isolated from the venom of the Australian elapid snake Pseudechis colletti and identified as phospholipases A showing close similarities in amino acid composition to a similarly acting enzyme from a sea snake venom (Enhydrina schistosa).

Mitochondria and sarcoplasmic reticulum as model targets for neurotoxic and myotoxic phospholipases A2

Certain neurotoxins and myotoxins from snake venoms have phospholipase A(2) activity (phosphatide 2-acylhydrolase, EC 3.1.1.4), which appears to be necessary for their toxicity. Several of these toxins inhibit the net uptake of Ca(2+) into sarcoplasmic reticulum vesicles and brain mitochondria. We have obtained evidence that the ability to inhibit this Ca(2+) uptake is a mechanistically relevant correlate of the toxicity of these proteins rather than being just a nonspecific consequence of their phospholipase A(2) activity. Two of the toxins, beta-bungarotoxin and notexin, had 5% and 50%, respectively, of the phospholipase A(2) activity of IVa phospholipase A(2)(a nontoxic enzyme), but beta-bungarotoxin was as effective as IVa in inhibiting Ca(2+) uptake into brain mitochondria and notexin was more effective. Each of the myotoxic enzymes substantially inhibited Ca(2+) uptake into sarcoplasmic reticulum, notexin being the most effective in this regard. This ability correlated better with their myotoxic potency than with their phospholipase A(2) activity. beta-Bungarotoxin lost its toxicity but not its measurable phospholipase A(2) activity after modification with ethoxyformic anhydride in the presence of dihexanoylphosphatidylcholine. The modified toxin also lost most of its ability to inhibit Ca(2+) uptake into sarcoplasmic reticulum and brain mitochondria. Sarcoplasmic reticulum vesicles reconstituted from solubilized sarcoplasmic reticulum retained their sensitivity to notexin.

Chemical modification of taipoxin and the consequences for phospholipase activity, pathophysiology, and inhibition of high-affinity choline uptake

Treatment of taipoxin with p-bromophenacyl bromide resulted in modification of single histidine residues in the alpha and beta subunits. The modification decreased the neurotoxicity (lethality) 350-fold, but the inhibitory action on high-affinity choline transport was reduced only threefold. The phospholipase activity and Ca2+-association constants for taipoxin and its subunits were determined. A model for the neurotoxicity of taipoxin indicates the alpha subunit as the ultimate cause of the disruption of synaptic transmission.

A harvester ant venom: chemistry and pharmacology

The mammalian toxicity of the potently algogenic venom of the ant Pogonomyrmex badius is greater than that reported for any other insect venom. This enzyme-rich venom contains high concentrations of phospholipase A2 and B, hyaluronidase, acid phosphatase, lipase, and esterases. This hemolytic secretion from the poison gland products unusual symptoms in mammals and appears to have been evolved as a deterrent for vertebrate predators.