Human Carbonic Anhydrases

Abstract

Detailed studies of a relatively large number of human erythrocyte carbonic anhydrases of different electrophoretic mobilities have shown that individually each is very similar to one of the major isozymes, either B or C. The enzymatic activities, the zinc, nitrogen, and amino acid contents, and the molecular weights of members of a given type are similar.Some differences in the tryptic peptides and in the amide contents of the more acidic carbonic anhydrase B type isozymes are seen.Incubation of either carbonic anhydrase B or carbonic anhydrase C at relatively high pH leads to the formation of more acidic isozymes of the same type.These forms generated in vitro appear to be identical with the same type carbonic anhydrases of similar electrophoretic properties isolated from erythrocytes.The B and C forms of erythrocyte carbonic anhydrases from a given species show distinct differences in concentration, enzymatic activity, amino acid composition, and other properties (l-9).The A isoeyme of humans appears to have a primary structure identical with that of the B form (1, 8, 9).Physicochemical studies of the various carbonic anhydrases isolated in our previous work (10) have revealed that the members of the immunological B and C classes have very similar properties.The major distinguishing differences are in their electrophoretic mobilities.The minor isozymes have also been generated in vitro from the B and C enzymes at relatively high PH.These artificially prepared isozymes are indistinguishable from the components of similar electrophoretic properties that are isolated from hemolysates.