Evidence was found for an inactive form of carbonic anhydrase type B in the erythrocytes of two children with primary renal tubular acidosis. The addition of zinc chloride to hemolysates from these patients resulted in a marked increase in the activity of this enzyme. No such effect was noted with hemolysates of control subjects. No significant differences were observed in the zinc levels of hemolysates of these patients and of normal individuals. However, the level of zinc in the carbonic anhydrase B isolated from one of these patients was low, suggesting a modified form of the enzyme. The restoration of activity upon the addition of zinc was reversed by ethylenediamine tetraacetate, but no such effects were noted for the carbonic anhydrase B of normal individuals. Thus the abnormal carbonic anhydrase B has decreased zinc binding. The ultraviolet difference spectrum of the carbonic anhydrase B of normal individuals and that of a patient showed a peak at 305 nm which decreased upon the addition of zinc. The abnormal form of carbonic anhydrase B was not distinguishable from that of normal individuals by either immunological or electrophoretic criteria.
T Kondo, N Taniguchi, K Taniguchi, I Matsuda, M Murao