The effect of implanted tumors on the oxidation of formate and of the methyl group of methionine in mouse liver.

The demonstration by Chance (2, 3) that catalase will catalyze the peroxidation of formate and the studies of Weinhouse and collaborators (6, 17) have suggested a possible function for catalase other than as a scavenging system for hydrogen peroxide. Mathews and Vennesland (16) and Rappoport et al. (18) have indicated that a DPNlinked formate dehydrogenase is absent in mam malian tissues and that peroxidation of formate by a catalase-hydrogen peroxide complex may be the sole route of oxidation in these preparations. Kruh0ffer (12) found an effect of DPN on the oxidation of formate in dialyzed rat liver prepara tions; but this may be explained by the finding of Nakada and Weinhouse (17) that such an effect is not only given by DPN, but by purine bases and ribotides as well. The latter workers also demon strated a rough parallelism between the catalase content of various rat tissues and the formateoxidizing activity. We were interested in a further investigation of these relations, particularly in reference to the de crease in liver catalase observed in many tumorbearing animals (9, pp. 518-40). The oxidation of formate in mouse liver homogenates has been in vestigated more fully, and it has been found that the oxidation of formate takes place at a reduced rate in liver homogenates from mice bearing the Ehrlich ascites carcinoma. Extending the present study to another aspect of formate metabolism, it was found that the rate of oxidation of the methyl group of methionine to formate in whole-cell