The 30 kDa abnormal protein in avian dystrophic muscle is indistinguishable from carbonic anhydrase III by physicochemical, immunological, and enzymological criteria.

In the accompanying paper, we described the existence, molecular characterization, and ontogeny of a 30 kDa abnormal protein in chicken dystrophic muscles. In this study, we have purified chicken carbonic anhydrase III and the 30 kDa protein and directly compared them. In terms of its enzymological features, the 30 kDa protein is a typical carbonic anhydrase III. Like carbonic anhydrases, it contains one mole zinc per mole of protein. The protein selectively cross-reacted with a chicken carbonic anhydrase III antibody. Antibody to the 30 kDa protein cross-reacted with chicken skeletal muscle carbonic anhydrase III. Moreover, the distribution of the abnormal protein is exactly identical to that of carbonic anhydrase III; however, there is a possibility that the 30 kDa protein is a variant of carbonic anhydrase III. Slight differences were found in antigenicities and in the apparent molecular weights of the two proteins. We have compared the two proteins by 125I-labeled two-dimensional peptide mapping. Tryptic maps have shown that the two proteins are highly homologous. Combined, these results strongly indicate that the 30 kDa protein and carbonic anhydrase III are similar, if not identical.