Renal carbonic anhydrase.

Carbonic anhydrase is a zinc metalloenzyme widely distributed throughout the tissues of the body. This enzyme exists in a number of isozymic forms in most mammalian species. Significant advances over the past decade have been made in characterizing the nature of renal carbonic anhydrase. In the kidney, this enzyme is thought to play a pivotal role in urinary acidification and bicarbonate reabsorption. Two distinct isozymes of carbonic anhydrase have now been identified in the mammalian kidney. A soluble cytoplasmic form, similar if not identical to human erythrocyte carbonic anhydrase C, accounts for the bulk of the renal carbonic anhydrase activity. In addition, a membrane-bound form constituting only about 2--5% of the renal activity has been found in the brush border and basolateral fractions of kidney homogenates. The histochemical and immunocytochemical localization of these isozymes along the nephron and collecting duct system of various mammalian species suggests that marked heterogeneity exists. The Editorial Review examines the biochemical and morphological approaches that have been used to elucidate the nature of renal carbonic anhydrase and to assess its distribution along the urinary tubule. Possible physiological roles for the renal carbonic anhydrases are considered for the different segments of the nephron and collecting duct system.