Properties of carbonic anhydrase isozymes isolated from porcine erythrocytes.

Two major components of carbonic anhydrase were purified from porcine red cells by column chromatography and electrofocusing techniques. Both forms behaved as single components in sedimentation velocity experiments and during starch gel electrophoresis. The observed molecular weight of both forms was about 3 x lo*. On the basis of their specific COZ hydrase activities and ammo acid compositions, these two carbonic anhydrase isozymes were designated as high activity (carbonic anhydrase C) or low activity (carbonic anhydrase B) forms which appear to be homologous to the high and low activity carbonic anhydrases, respectively, of other mammals. When these pig B and C isozymes were compared with the red cell carbonic anhydrases of other ungulates (cattle and horse), several interesting features were observed. In contrast to the electrophoretic gel patterns of the horse B and C isozymes in which the C form is markedly more basic than the B form, the high activity C form of pig was observed to be more acidic than the low activity B form. The tryptic peptide map of bovine carbonic anhydrase appears to be more similar to that of porcine carbonic anhydrase C than to B, indicating that they are probably homologous proteins. Neoprontosil binding by the pig and horse B isozymes give rise to essentially identical spectra in the 425to 600-rnp region, whereas the C isozymes, from these two sources, generate quite different spectra.