Properties of specific binding site of myotoxin a, a powerful convulsant, in brain microsomes.
Myotoxin a, a small basic polypeptide from prairie rattlesnakes (Crotalus viridis viridis), induces myonecrosis and binds to a single class of binding sites in skeletal muscle sarcoplasmic reticulum. In the present study, [125I]myotoxin a with a high specific activity was prepared and it was shown to bind mainly to microsomes in rat whole brain. [125I]Myotoxin a was further shown to bind to microsomes prepared from all regions tested in brain. Its specific binding to whole brain microsomes was of approximately 1.9 times lower affinity (KD = 0.76 microM; Bmax = 13.1 nmol/mg) than that to skeletal muscle sarcoplasmic reticulum. [125I]Myotoxin a binding to brain microsomes was displaced by unlabeled myotoxin a with an IC50 value of 4.5 microM. [125I]Myotoxin a binding was markedly reduced by treatment of microsomes with trypsin, suggesting that the binding site of [125I]myotoxin a is partially proteins. The binding was significantly inhibited by Mg2+ at concentrations above 1 mM. Having looked at several drugs, we noted that [125I]myotoxin a binding was noncompetitively inhibited by spermine, whereas it was enhanced by heparin. On the other hand, the i.c.v. injection of myotoxin a in mice induced potent convulsive effects at 0.05 nmol/mouse or more. This paper is the first to show that the specific binding site of myotoxin a is present in mouse brain and that myotoxin a is a novel peptidic convulsant in mice.
Katagiri
C
C
Department of Pharmaceutical Molecular Biology, Faculty of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Japan.
Ishikawa
H H
HH
Ohkura
M
M
Nakagawasai
O
O
Tadano
T
T
Kisara
K
K
Ohizumi
Y
Y
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D003435:Crotalid Venoms / Q000378:metabolism* / Q000633:toxicity; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D008861:Microsomes / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D003435:Crotalid Venoms; C018932:myotoxin A