IMMUNOGLOBULIN SYNTHESIS AND SECRETION I. Biosynthetic Studies of the Addition of the Carbohydrate Moieties

This study was designed to determine the time in the intracellular life of immunoglobulin when the carbohydrate moieties are added . Plasma cells from a mouse myeloma tumor were exposed to glucosamine-3H (a "bridge" sugar), galactose-3H, or leucine3H. With each of the above isotopes, the percentage of total radioactive immunoglobulin that has been secreted after different periods of labeling and the extent to which puromycin prevented incorporation into immunoglobulin were determined . The results indicate that both galactose and glucosamine (in its N-acetyl form) become covalently incorporated into immunoglobulin G late in its intracellular life and suggest that glucosamine is also added onto nascent polypeptide chains (i .e ., on polyribosomes) . The purpose of the present studies was to investigate further the time in the intracellular life of IgG when glucosamine and galactose are incorporated into the carbohydrate portion of the molecule. The approaches used were to measure : (a) the extent to which puromycin can prevent incorporation of galactose or glucosamine into intracellular and secreted IgG ; (b) the percentage of total radioactive IgG secreted after different periods of time of labeling with leucine, galactose,