Primary structure of human carbonic anhydrase C.

The primary structure of human erythrocyte carbonic anhydrase C has been determined. The single polypeptide chain contains 259 amino acid residues devoid of disulfide bridges. The experimental approach has involved restriction of the action of trypsin to arginyl bonds by amidination of the lysyl side chains. The six tryptic fragments obtained have been separated and sequenced by manual techniques. During the sequence work on human carbonic anhydrase C, 3 very easily deamidated asparagine residues were noted, all occurring in -Asn-Gly- sequences. The deamidation which takes place even under normal conditions of peptide preparation seems to be associated with a beta-aspartyl shift. A few minor differences existing between our structure and the results from another laboratory are discussed. A brief comparison is made with the primary structures of other carbonic anhydrases with regard to the function of some amino acid residues in the active site of the enzymes.