A study of some mitochondrial and peroxisomal enzymes in human colonic adenocarcinoma

Three mitochondrial enzymes, cytochrome oxidase, succinate dehydrogenase, and monoamine oxidase, and two peroxisomal enzymes, catalase and urate oxidase, were measured spectrophotometrically in the postnuclear supernatant prepared from homogenates of normal mucosa and carcinoma of the human colon. The specific activities, in both normal mucosa and carcinoma, varied from patient to patient. However, the difference in these activities between normal mucosa and carcinoma was consistent when patients were compared. The activities of cytochrome oxidase, succinate dehydrogenase, monoamine oxidase, and catalase were greater in normal mucosa than in carcinoma. In contrast, urate oxidase activity increased in carcinoma as compared with normal mucosa. Furthermore, cytochrome oxidase and succinate dehydrogenase decreased proportionally in carcinoma, supporting the concept that the mitochondrial respiration in normal tissue and carcinoma is quantitatively but no qualitatively changed. However, the decrease in monoamine oxidase activity in carcinoma was greater than that observed with other mitochondrial enzyme activities and was irregular. This suggests that a qualitative mitochondrial change may occur in carcinoma. In particular, the ratio between outer membrane enzyme activity and respiratory enzyme activity may be altered.