Evidence for a specific protein associated to the plasma membrane of cholinergic synaptosomes

Synaptosomal plasma membrane fractions were prepared by fractionation of pure Torpedo cholinergic synaptosomes. A 67 000 dalton peptide was shown to be a major component of the presynaptic membrane. It appears specific for this membrane since (1) it copurifies with the synaptosomal plasma membrane; (2) it was not present in similar plasma membranes but prepared from Torpedo electric lobes or electric nerves, and since (3) rabbit antibodies to presynaptic antigens which were mainly directed to this 67 000 dalton peptide band were shown to bind to the nerve terminal network in Torpedo electric organ. A crude fraction of presynaptic plasma membrane prepared from electric organ homogenate could be a convenient material for the purification of this 67 000 dalton peptide.