Inhibition of the succinoxidase system by extracts of tumour and normal tissues

Abstract

The aerobic oxidation of succinate with liver suspensions was strongly inhibited by suspensions or extracts of various tissues, especially of certain tumors, pancreas, and spleen. The inhibitor was non-dialysable and, to some extent, thermolabile. Commercial trypsin in small amts. was also inhibitory. The succinic dehydrogenase (anaerobic reduction of methylene blue with succinate) and the cytochrome oxi-dase (oxidation of p-phenylene diamine in the presence of added cytochrome c) were both inhibited by tumor extracts, but not strongly enough to account for the main effect of the inhibitor on the complete succinoxidase system of liver. Cytochrome c was probably not affected. The inhibitor acted particularly strongly on some other component of the succinoxidase system of liver, possibly cytochrome b. Kidney suspensions were affected similarly to liver suspensions. The succinoxidase activity of brain and muscle suspensions was also inhibited; but the succinoxidase activity of heart suspensions was scarcely at all affected and tumor extracts actually provoked an acceleration of succinate oxidation with heart suspension in the presence of added cytochrome c. The oxidation of p-phenylene diamine with heart was inhibited by tumor extract in the absence of added cytochrome c, but not in its presence.