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

A soluble carbonic anhydrase (carbonate hydro-lyase, EC 4.2.1.1) has been purified to homogeneity from the membranous lateral wall (stria vascularis, spiral ligament, spiral prominence, and outer sulcus) of the guinea-pig inner ear. About 1% of the protein of the membranous lateral wall is carbonic anhydrase. The specific activity of the enzyme in homogenates of the lateral wall is 1.6-1.8 times that of whole blood; for homogenates of the components, stria vascularis and the fraction containing the spiral ligament, the specific activities are 0.9 and 2.0 times the specific activity of whole blood, respectively. No other cochlear fraction examined contains appreciable carbonic anhydrase. The purified enzyme has a molecular weight of about 30,000, a specific activity 60--80% that of carbonic anhydrase C from blood, and an electrophoretic mobility similar to that of the blood enzyme. Cochlear carbonic anhydrase is half-maximally inhibited by 4 X 10(-9) M acetazolamide, is completely inhibited above 10(-5)M acetazolamide, and forms a fluorescent complex with 5-dimethylaminonaphthalene-1-sulfonamide, by which it can be distinguished on polyacrylamide gels. This report describes both another isolation of a carbonic anhydrase from a source other than blood and the isolation of an inner-ear enzyme.