PRESENCE OF CARBONIC ANHYDRASE-III IN ERYTHROCYTE

It is well known that there is present in hemolyzed serum a factor that interferes with the radioimmunoassay for detection of skeletal muscle carbonic anhydrase III (CA-III) in serum. This inhibitory factor cross-reacts with muscle anti-CA-III antibody and its level increases in parallel with the degree of hemolysis. In order to identify this factor, we purified the factor from a hemolysate of human erythrocytes, characterized it, compared it with known carbonic anhydrase isozymes from erythrocytes and with CA-III from skeletal muscle. We concluded that the factor was biochemically and immunochemically identical to CA-III from skeletal muscle. Calculation indicated the factor to represent about 1% of the total enzymes in human erythrocytes.