DIFFERENTIAL EXPRESSION OF GALNAC-4-SULFOTRANSFERASE AND GALNAC-TRANSFERASE RESULTS IN DISTINCT GLYCOFORMS OF CARBONIC-ANHYDRASE-VI IN PAROTID AND SUBMAXILLARY-GLANDS

Differential expression of glycosyltransferases has the potential to g enerate functionally distinct glycoforms of otherwise identical protei ns. We have previously demonstrated the presence of unique oligosaccha rides terminating with GalNAc-4-SO4 on the pituitary glycoproteins lut ropin (LH), thyroid stimulating hor mone (TSH), and pro-opiomelanocort in (POMC). A glycoprotein hormone:GalNAc-transferase and a GalNAc-4-su lfotransferase are present in the pituitary and can account for the sy nthesis of these unique oligosaccharides on specific glycoproteins. Bo th transferases are coordinately expressed in a number of tissues in a ddition to pituitary, including submaxillary gland, lacrimal gland, an d kidney, suggesting that additional glycoproteins bearing oligosaccha rides terminating with GalNAc-4-SO4 are synthesized in these tissues. In this study we show that while the glycoprotein hormone:GalNAc-trans ferase and the GaLNAc-4-sulfotransferase are coordinately expressed in bovine submaxillary gland, the GalNAc-transferase is expressed in the parotid gland in the absence of the GalNAc-4-sulfotransferase. The re lative expression of these two transferases in submaxillary and paroti d glands correlates with the presence of unique Asn-linked oligosaccha rides on carbonic anhydrase VI (CA VI) synthesized in each of these ti ssues. The majority of Asn-linked oligosaccharides on CA VI synthesize d in submaxillary gland terminate with GalNAc-4-SO,, In contrast, CA V I which is synthesized in bovine parotid gland bears oligosaccharides which terminate predominantly with beta 1,4-linked GalNAc which is not sulfated. The presence of different terminal residues on the Asn-link ed oligosaccharides of submaxillary and parotid CA VI thus correlates with the complement of transferases in these glands and suggests diffe ring biological roles for submaxillary and parotid CA VI.