Carbonic anhydrase C in the human renal medulla

Soluble carbonic anhydrase (carbonate dehydratase, EC 4.2.1.1) from the papillary and inner medullary regions of thoroughly perfused human donor kidneys was isolated by affinity chromatography. The purified enzyme was homogenous with respect to sedimentation in the ultracentrifuge and iso-electric focusing. It had an amino-acid composition and behaved chromatographically, kinetically, electrophoretically and immunochemically like the high-activity (with respect to CO2) erythrocyte carbonic anhydrase HCA-C, and the renal enzyme previously isolated from extracts of the whole kidney. The results suggest that all regions of the human kidney contains one soluble form of carbonic anhydrase similar to and probably identical with HCA-C. Small immunoassayable amounts (1/30 of total enzyme protein) of the low-activity erythrocyte isoenzyme HCA-B were also found, but are considered to be a contaminant. There was no indication for the presence of sulfonamide-resistant isoenzymes.