STUDIES ON SHELL FORMATION. V. THE INHIBITION OF SHELL FORMATION BY CARBONIC ANHYDRASE INHIBITORS

¹ Department of Zoology, Duke University, Durham, N. C.

1. The carbonic anhydrase inhibitors 2-benzothiazolesulfonamide (Cpd. I) and 2-acetylamino-1,3,4-thiadiazole-5-sulfonamide (Diamox) (Cpd. II) markedly reduced the rate of deposition of calcium in the shell of the oyster Crassostrea virginica. Treatment of oysters with Cpd. I, 1:80,000, for 7-8 hours reduced the rate to one-tenth the normal value and gave essentially complete inhibition at higher concentrations. The latter result indicates that inhibition by this compound is not limited to carbonic anhydrase. With Cpd. II the maximum inhibition was 50% and was produced at a concentration of 1:100,000 or higher.

2. Measurements of shell movements and oxygen consumption of mantle tissue showed that concentrations of carbonic anhydrase inhibitors which had a marked inhibitory action on calcium deposition exerted no general toxic action on the oyster.

3. The rate of calcium deposition of the oyster was more than 9 times that of the isolated mantle-shell preparation, confirming an earlier study. The addition of 0.01 M oxaloacetate to the mantle-shell preparation increased the deposition rate more than 4-fold, suggesting the utilization of metabolic CO₂ for shell carbonate by the organism. Succinate and malate were without significant effect on calcium deposition.

4. The experimental findings support the view that carbonic anhydrase increases calcium deposition in the oyster when the rate is sufficiently high that either of the following reactions becomes limiting: CO₂ + H₂OH₂CO₃; CO₂ + OH^- HCO₃^-. At lower rates the enzyme would not be required.