THE INHIBITION OF CARBONIC ANHYDRASE AND OF GASTRIC ACID SECRETION BY THIOCYANATE

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Abstract
Carbonic anhydrase from human or dog blood and human or dog gastric mueosa is inhibited by SCN-. The inhibition apparently depends upon the formation of a catalytically inactive, dissociable compound between 1 mol of SCN- and 1 mol of enzyme. The constant for the equation [SCN-] [Active carbonic anhydrase] = K [Inactive carbonic anhydrase] at pH 6.8 and 0[degree]C. is 0.62 X 10-3. NaSCN when fed to dogs reversibly inhibits the secretion of acid by the gastric mueosa. As SCN- in the gastric juice increases the conc. of H+ and Cl- in the gastric secretion decreases. The inhibition is best explained by the assumption that SCN- inhibits the carbonic anhydrase which is a part of the secretory mechanism. The relation between SCN- conc. in the secretory mechanism and the degree of inhibition shows that the rate of secretion of acid by the gastric mueosa is directly proportional to the rate of formation of carbonic acid in the parietal cells.

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