Human Renal Carbonic Anhydrase. Purification and Properties

Abstract

Carbonic anhydrase was isolated from fresh human donor kidneys which had been thoroughly perfused free from blood. The isolation procedure involved biospecific affinity chromatography on a sulfanilamide -agarose column and yielded one soluble form of the enzyme, which was homogenous with respect to sedimentation in the ultracentrifuge, electrophoresis, isoelectric focusing and immunodiffusion. The renal enzyme had an amino acid composition and behaved chromatographically, electrophoretically, and immunochemically like the erythrocyte form human carbonic anhydrase C, isolated by the same technique. The kinetic behaviour of the renal enzyme was similar to that of human carbonic anhydrase C when compared by the stopped-flow pH-indicator technique.The results therefore suggest that the cytoplasmic carbonic anhydrase of the human kidney is very similar, if not identical, to the high-activity erythrocyte form of human carbonic anhydrase C.Carbonic anhydrase (carbonate hydro-lyase) is needed for the acidification of the urine, and inhibitors of the enzyme are used therapeutically as diuretic agents [l]. It would, therefore, appear important to know the properties of the enzyme. However, it has not yet been purified to an extent which would allow a more detailed characterization. This would seem even more necessary in view of recent reports which indicate that various tissues contain different forms of the enzyme with different properties and perhaps functional significance [2]. Even a single cell like the human erythrocyte contains two forms of the enzyme, which are very different with respect to amino-acid composition and kinetic activities [3]. It is not yet known whether the kidney and erythrocytes use the same or different forms of the enzyme.The present paper describes the isolation and properties of the major human renal enzyme in comparison with the erythrocyte enzymes. Advantage has been taken of the access to virtually blood-free donor kidneys and a new affinity chromatographic technique for the purification of carbonic anhydrase.Abbreviations. HCA C and HCA B are isoenzymes of carbonic Enzyme. (CBN Recommendations 1972). Carbonic anhydrase anhydrase from human erythrocytes.

Spontaneous luminal disequilibrium pH in S3 proximal tubules. Role in ammonia and bicarbonate transport.

“…Two forms of carbonic anhydrase exist in the kidney, a soluble cytoplasmic enzyme and a membrane-bound form (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Cytoplasmic carbonic anhydrase is thought to supply protons in the cell for transport across the apical membrane by catalyzing the formation ofcarbonic acid from CO2 and water.…”

Calcium-regulating hormones modulate carbonic anhydrase II in the human erythrocyte.

“…The apparent function of the enzyme in this location is to promote the dehydration of serum bicarbonate to yield CO2 that can readily diffuse across the endothelial barrier in expiration. Recently, Whitney and Briggle (33) suggested that membrane-associated carbonic anhydrase in lung is the same as that reported in the brush-border of the kidney tubules and is very similar to the high-activity enzyme (34).…”

Purification of a carbonic anhydrase from the inner ear of the guinea pig.

“…Carbonic anhydrases have been purified to homogeneity from several tissues other than blood, namely, kidney (20), liver (21), gastrointestinal mucosa (17), uterus (22), and prostate gland (23). The present purification of carbonic anhydrase from the guinea pig cochlea has revealed a major soluble enzyme that is similar, but not necessarily identical to the high-specificactivity isoenzyme from blood, carbonic anhydrase C. Points of similarity include electrophoretic mobility, elution position on anion-exchange columns, and specific activity.…”