Complete amino acid sequence of ovine salivary carbonic anhydrase

The primary structure of the secreted carbonic anhydrase from ovine salivary glands has been determined by automated Edman sequence analysis of peptides generated by cyanogen bromide and tryptic cleavage of the protein and Staphylococcus aureus V8 protease, trypsin, and alpha-chymotrypsin subdigests of the large cyanogen bromide peptides. The enzyme is a single polypeptide chain comprising 307 amino acids and contains two apparent sites of carbohydrate attachment at Asn-50 and Asn-239. The protein contains two half-cystine residues at 25 and 207 which appear to form an intramolecular disulfide bond. Salivary carbonic anhydrase shows 33% sequence identity with the ovine cytoplasmic carbonic anhydrase II enzyme, with residues involved in the active site highly conserved. Compared to the cytoplasmic carbonic anhydrases, the secreted enzyme has a carboxyl-terminal extension of 45 amino acids. This is the first report of the complete amino acid sequence of a secreted carbonic anhydrase (CA VI).