Carboxyl-terminal region of human and bovine erythrocyte carbonic anhydrases. I. Amino acid sequences of terminal cyanogen bromide fragments.

Abstract

Carboxyl‐terminal sequences have been determined for forms B and C of the human erythrocyte carbonic anhydrase and form B of the bovine enzyme. The proteins were degraded with CNBr, and peptide fragments of 20 residues were isolated from human enzyme C and bovine enzyme B while the human B form gave a fragment consisting of only 19 residues. The sequences of these fragments were determined and by carboxypeptidase digestion of the whole proteins it was shown that they represent the carboxyl‐terminal part of the proteins. Comparison of the sequences of the enzymes gives strong support for evolutionary homology. Greater similarities in sequence are found between bovine carbonic anhydrase and human carbonic anhydrase C than between the two forms of the human enzyme. All sequences contain an Arg‐Pro peptide bond. In two of the sequences this bond was found to be hydrolyzable with trypsin.