THE METABOLIC-ACTIVATION OF CYANAMIDE TO AN INHIBITOR OF ALDEHYDE DEHYDROGENASE IS CATALYZED BY CATALASE

The inhibition of aldehyde dehydrogenase by cyanamide [an alcohol deterrent agent] is dependent on an enzyme catalyzed conversion of the latter to an active metabolite. Catalase is apparently the enzyme responsible for this bioactivation. The elevation of blood acetaldehyde elicited by cyanamide after ethanol administration to rats was attenuated more than 90% by pretreatment with the catalase inhibitor, 3-amino-1,2,4-triazole. This attenuation was dose-dependent and was accompanied by a reduction in total hepatic catalase activity. Although hepatic catalase was also inhibited by cyanamide, a positive correlation between blood acetaldehyde and hepatic catalase activity was observed. In vitro, the activation of cyanamide was catalyzed by the rat liver mitochondrial subcellular fraction, the 50-65% ammonium sulfate mitochondrial fraction and purified bovine liver catalase. Cyanamide activation was inhibited by sodium azide. Since much of the hepatic catalase is localized in the peroxisomes and since peroxisomes and mitochondria cosediment, the cyanamide activating enzyme, catalase, is apparently peroxisomal and mitochondrial origin.