1 crotapotin , the acidic subunit of crotoxin , greatly potentiated the presynaptic effect of isolated basic phospholipase a ( pla ) of crotoxin in both mouse diaphragm and chick biventer cervicis muscles whereas the myotoxic effect was not affected significantly.2 in contrast to crotoxin pla , the presynaptic effects of notexin and notechis-5 , self-active single chain toxins , were antagonized by crotapotin while actions of beta-bungarotoxin were not affected.3 by assaying pla activity , crotoxin pla was found to be unstable in physiological salt solution , especially when in contact with muscle , due to massive non-specific binding to and destruction by the muscle.4 the decline of crotoxin pla was greatly reduced by the presence of crotapotin but not by another acidic protein , volvatoxin a ( 2 ) , or heparin.5 notechis-5 was found to be stable even when in the presence of muscles.6 [ ( 3 ) h ] -acetylated crotoxin pla , which retained about 40 % of its original enzyme and presynaptic blocking activities , also bound rapidly to the mouse diaphragm on incubation and this binding was greatly hindered by the simultaneous addition of crotapotin.7 the prevention of binding of crotoxin pla by crotapotin occurred mostly at those sites where the binding was easily dissociable on washing .
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