PURIFICATION AND SEQUENCE DETERMINATION OF A NEW MUSCARINIC TOXIN (MT4) FROM THE VENOM OF THE GREEN MAMBA (DENDROASPIS-ANGUSTICEPS)

A toxin which partially inhibited [H-3]N-methylscopolamine binding to rat brain muscarinic receptors was purified from the venom of green ma mba, Dendroaspis angusticeps. The N-terminal sequence (up to 45 amino acids) was determined by automated Edman degradation of the whole mole cule. The complete sequence was elucidated after enzymatic cleavage wi th endoproteinase Arg-C or endoproteinase Lys-C and peptide fragments purification. The identity of the C-terminal amino acid was confirmed by hydrazinolysis. The new toxin (MT4) had eight half-cystines and 66 amino acids. It differed from muscarinic toxin MT1 by a single substit ution in position 57 (arginine in MTI, histidine in MT4), proximal to the sixth half-cystine.