Purification and Properties of Three Pig Erythrocyte Carronic Anhydrases

Three distinct forms of the zinc containing enzyme carbonic anhydrase were isolated from pig erythrocytes. One low activity type enzyme and two genetic variants of the high activity type enzyme with identical CO2 hydratase activities which were 8 times as high were isolated from Danish Black and White Swine. In the isolation procedure described, the hemoglobin was eliminated by precipitation with chloroform-ethanol, and the isoenzymes were separated by DEAE-Sephadex chromatography. A number of enzymatically active minor components were separated. They were apparently all genetically linked to one of the three major components. The three purified isoenzymes behaved as homogeneous components during isoelectric focusing and electrophoresis at different pH values. They were characterized in terms of molecular weight, isoelectric pH, zinc content, amino acid composition, and enzymatic activity against CO2, p-nitrophenyl acetate, and β-napthyl acetate. The circular dichroism of the enzymes in the ultraviolet region was studied. The properties of the enzymes were similar to those of carbonic anhydrases of corresponding types isolated from other mammalian species. Sulphur containing amino acid residues were absent in the low activity type enzyme. The amino acid composition of the two high activity mutants deviated only in that an arginine residue in the most widespread genetic variant was replaced by a histidine residue in the less frequent variant. Otherwise the two mutants showed identical properties.