A novel low-activity form of carbonic anhydrase I in erythrocytes of patients with primary aldosteronism. Evidence for the presence of a mixed disulfide with glutathione.

A low-activity form of erythrocyte carbonic anhydrase isozyme I was found in patients with primary aldosteronism. The specific activity was very low, but the activity was restored by drug treatment as well as adrenalectomy. The enzyme was purified to homogeneity from one of the patients. With respect to its antigenicity and zinc content, the low-activity form was not distinguishable from the normal enzyme. On the other hand, the inhibition constant and binding affinity to acetazolamide of the low-activity enzyme were lower than those of normal enzyme. Sulfhydryl group titration, amino acid analysis, and peptide-mapping analysis suggested that the low-activity enzyme contains a mixed disulfide with glutathione which is closely associated with its low activity.