CHARACTERIZATION AND TOPOGRAPHY OF THE GLYCOPROTEINS OF ADRENAL CHROMAFFIN GRANULES

The glycoproteins of the membranes of bovine chromaffin granules were characterized by two polyacrylamide gel electrophoresis systems. Five components (I-V) were demonstrated with apparent molecular weights ranging in the unreduced form from 45,000 to 150,000. Glycoprotein I was identified as the enzyme dopamine β-hydroxylase. Four of these glycoproteins (with the exception of component IV) were apparently also present in the membranes of pig and horse chromaffin granules. The soluble proteins of chromaffin granules contained at least three glycoproteins. Only glycoprotein I (dopamine β-hydroxylase) was present both in the soluble content and in the membranes of chromaffin granules. Affinity chromatography with lectins demonstrated that from the soluble proteins only dopamine β-hydroxylase was adsorbed by concanavalin A, whereas none of these proteins reacted with wheat germ lectin and Ricinus communis agglutinin. Three membrane proteins including dopamine β-hydroxylase and glycoprotein II as major components were adsorbed by concanavalin A, whereas wheat germ lectin bound only component II and a small amount of component III. By electron microscopy it was demonstrated that concanavalin A did not bind to intact chromaffin granules whereas ruthenium red and cationized ferritin did. Isotope labelling after galactose oxidase treatment revealed that at least the carbohydrate portion of the major glycoproteins is present on the inner side of the granule membranes facing the content.