Identification of a Proteoglycan Antigen Characteristic of Cholinergic Synaptic Vesicles

An antiserum to cholinergic synaptic vesicles isolated from the electric organ of Torpedo marmorata was purified by adsorption with fractions containing unwanted antigens. The adsorbed antiserum responds to the proteoglycan core material of the cholinergic synaptic vesicles. The major antigen migrates in an anomalous fashion on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), forming a broad band with an apparent molecular weight of approximately 120,000 - 300,000. The distribution of this antigen after sucrose density gradient centrifugation of synaptic vesicles is the same as that of vesicular ATP. The antigen comigrates with a substance that can be stained with Alcian-Blue after SDS-PAGE of highly purified synaptic vesicles. This substance is related to the low-molecular-weight, Alcian-Blue-positive glycosaminoglycan vesiculin, which is formed from the high-molecular-weight proteoglycan by prolonged dialysis against water or by protease treatment. No antibodies were detected against vesiculin itself, indicating that the antigenic determinants are restricted to the proteoglycan.