ENZYME INHIBITION BY DERIVATIVES OF PHENOTHIAZINE: III. CATALASE, CYTOCHROME OXIDASE, AND DEHYDROGENASES

Abstract

The inhibition of liver catalase and of cytochrome oxidase by leucophenothiazone has been confirmed by manometric methods. Phenothiazine sulphoxide is a powerful catalase inhibitor, its activity being much greater at pH 5.3 than at neutrality.The succinoxidase activity of beef heart is inhibited by phenothiazone and by thionol. Phenothiazone in its oxidized form acts upon the succinic dehydrogenase, while the leuco form inhibits the cytochrome oxidase.Phenothiazone is reduced by the yeast lactic dehydrogenase system, and the enzyme activity is markedly decreased. Urease is also partially inhibited, whereas the effect of phenothiazone upon d-amino-acid oxidase is almost negligible.The possible relationship of these findings to the action of phenothiazine upon living organisms is discussed.