Synaptic localization and neural regulation of an N-acetylgalactosaminyl transferase in skeletal muscle.

We have previously documented the properties of a approximately 220-kDa cell surface glycosyltransferase that transfers N-acetylgalactosamine to oligosaccharide chains (Balsamo et al., 1986b). Because N-acetylgalactosamine-terminated carbohydrates are concentrated at the neuromuscular junction (Scott et al., 1988), we assayed skeletal muscle for the presence of the N-acetylgalactosaminyl transferase. Using immunohistochemical methods, we found that the enzyme is localized at neuromuscular junctions on normal adult rat muscle fibers. Biochemical assays confirm that junctional areas are highly enriched in the approximately 220-kDa immunoreactive species as well as in enzyme activity associated with the approximately 220-kDa species. This restricted distribution is dependent on synaptic integrity, as the enzyme appears extrasynaptically on denervation. These results provide a plausible metabolic basis for the localization of a synapse-specific carbohydrate and demonstrate that the expression of a glycosyltransferase is regulated by synaptic interactions.