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Comparison of Transhydrogenase and Pyridine Nucleotide-Cytochrome c Reductase Activities in Rat Liver and Novikoff Hepatoma^*

Baltazar Reynafarje and Van R. Potter

( McArdle Memorial Laboratory, Medical School, University of Wisconsin, Madison, Wis.)

1. Pyridine nucleotide-cytochrome c reductases and transhydrogenase have been examined in whole homogenate and in cell fractions of normal rat liver and Novikoff hepatoma.

2. DPNH-cytochrome c reductase was present in mitochondria and microsome fractions from both liver and hepatoma.

3. In liver the enzyme transhydrogenase was limited to the mitochondria and was firmly attached to the nonsoluble part of this cell fraction. It was absent from the microsome and soluble fractions.

4. Transhydrogenase was absent or present only to a negligible extent in whole homogenate and cell fractions from Novikoff hepatoma, under the conditions employed thus far.

5. There was a true TPNH-cytochrome c reductase in mitochondria and microsomes from normal liver.

6. TPNH-cytochrome c reductase from liver was firmly associated with microsomes but was readily dissociated from mitochondria, passing into a form that was not sedimented at a speed of 105,000 x g. This soluble fraction did not contain DPNH-cytochrome c reductase.

7. TPNH-cytochrome c reductase activity was absent or present in negligible amounts in whole homogenate and cell fractions of Novikoff hepatoma, as determined by the present method.

^* This work was supported in part by a grant (No. C-646) from the National Cancer Institute, National Institutes of Health. A preliminary report was given at the Annual Meeting of the American Association for Cancer Research and reported in Proc. Am. Assoc. Cancer Research, 3:241, 1957.

Rockefeller Foundation Fellow, 1955–1957; Present address, Departamento de Fisiopatologia, Facultad de Medicina, Universidad de San Marcos, Lima, Peru.

Received 7/ 8/57.