Re-examination of crotoxin-membrane interactions.
The interaction of crotoxin with synaptic membranes from Torpedo marmorata has been re-examined, using radioiodinated toxin. In competition experiments, the 'saturable binding' is usually calculated by subtracting the non-saturable binding, determined in the presence of an excess of unlabelled crotoxin, from total binding. Paradoxically, we observed a notable increase of the 'saturable binding' of 125I-crotoxin, defined in this manner in the presence of a high concentration of certain competitors (e.g. crotoxin subunit B, agkistrodotoxin, ammodytoxin and ammodytin I2). This potentiation effect was analysed by competition and cross-linking experiments. The dissociation of the basic crotoxin subunit CB, which differs markedly from crotoxin in its membrane-binding characteristics, was found to be the main reason for the observed phenomenon. 125I-CB could be released from 125I-crotoxin by exchange with a molecule having sufficient affinity towards CA (e.g. CB or agkistrodotoxin) or it could be dissociated from the specific crotoxin membrane-binding site(s) by a competitor molecule. Our results, therefore, suggest a reinterpretation of previous 125I-crotoxin binding studies.
Unité des Venins, Institut Pasteur, Paris, France.
I
I
Krizaj
G
G
Faure
F
F
Gubensek
C
C
Bon
D000818:Animals; D001667:Binding, Competitive; D003432:Cross-Linking Reagents / Q000378:metabolism; D003435:Crotalid Venoms / Q000302:isolation & purification / Q000378:metabolism*; D003439:Crotoxin / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D011869:Radioligand Assay; D013570:Synaptic Membranes / Q000378:metabolism*; D014101:Torpedo
D003432:Cross-Linking Reagents; D003435:Crotalid Venoms; D007457:Iodine Radioisotopes; D003439:Crotoxin