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J MacDermot

Publications and source records attributed to J MacDermot.

97 records · Page 6Linked to original sources
PubMed1978

beta-Bungarotoxin. Separation of two discrete proteins with different synaptic actions.

beta-Bungarotoxin, a specific presynaptic blocking agent, was prepared in two stages from the crude venom of Bungarus multicinctus by ion-exchange chromatography on the weakly acidic ion exchanger, CM-Sephadex, and on the strongly acidic ion exchanger, sulphopropyl-Sephadex. By these procedures it was purified to a single protein, which was shown by reduction to contain two polypeptide chains with mol.wts. of less than 15000. During purification of beta-bungarotoxin three other proteins were isolated. Two of these proteins have similar molecular weights, subunit structure and physiological properties to the major protein component. This latter is referred to as beta-bungarotoxin, since it has the same physiological properties as those described for unpurified beta-bungarotoxin by other workers. The first protein has very different physiological effects and biochemical properties from beta-bungarotoxin. This protein has a single class of polypeptide chains with an apparent molecular weight that is lower than the main beta-bungarotoxin protein, and appears to block synaptic transmission by a predominantly postsynaptic effect. It has been suggested [Oberg & Kelly (1976) J. Neurobiol. 7, 129-141] that the action of beta-bungarotoxin depends on its phospholipase A activity; however, in this preparation of the toxin less than 50 muunits of phospholipase A activity were detected (1 unit of activity is the amount of enzyme forming 1 mumol of L-alpha-phosphatidylcholine/min per mg of protein).

Animals↗
PubMed1978

beta-Bungarotoxin. The binding of [3H]pyridoxylated beta-bungarotoxin to a high-molecular-weight protein receptor.

beta-Bungarotoxin was labelled with pyridoxal 5'-phosphate (incorporating 3H). The kinetics of beta-bungarotoxin binding to several tissue subfragments of nervous tissue was studied. The dissociation constant of 3H-pyridoxylated beta-bungarotoxin in this reaction was 0.21-0.37 micron and that of unlabelled beta-bungarotoxin was 25 nM. Hill [(1910) J. Physiol. (London) 40, iv-vii] and Scatchard [(1949) Ann. N.Y. Acad. Sci. 51, 660-672] analyses demonstrated no co-operativity of binding and only a single class of receptor sites, consistent with a bimolecular association of beta-bungarotoxin and its receptor. The iodinated toxin was physiologically inactive. Toxin was bound in non-specific unsaturable fashion by glass and/or plastic. This low-affinity binding was corrected by addition of bovine serum albumin to a final concentration of 30 mg/ml. A soluble protein receptor of beta-bungarotoxin was isolated and the mol.wt. is approx. 200000.

Animals↗