Human Carbonic Anhydrases

Sequence studies of human erythrocyte carbonic anhydrase C show that it is a single chain of 259 amino acid residues. A series of relatively small, soluble peptides obtained by chymotryptic and tryptic digestion of heat denatured enzyme, large peptides produced by tryptic cleavage at arginine residues of maleylated enzyme, as well as those resulting from further enzymatic cleavage of these peptides, and a cyanogen bromide cleavage product served as the materials for deriving the primary structure. The over-all sequence reveals that 60% of the residues in the human B and C forms of the enzymes are identical in homologous position. Most of the differences result from a single base substitution in the responsible codon.