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The Oxidation of Extramitochondrial Reduced Diphosphopyridine Nucleotide in Ascites Tumor Cells¹

The Department of Experimental Medicine and Cancer Research, The Hebrew University-Hadassah Medical School, Jerusalem, Israel

The capability of oxaloacetate and -ketoglutarate to replace pyruvate in its interconversion with lactate in the presence of Landschuetz ascites tumor cells was investigated. Using lactate-1-¹⁴C, it was shown that oxaloacetate brought about a considerable accumulation of pyruvate-1-¹⁴C and stimulated both O₂ consumption and ¹⁴CO₂ production. Oxaloacetate also enhanced the removal of lactate and its conversion to pyruvate, mediated by the supernatant of the sonically disrupted tumor cells and diphosphopyridine nucleotide (DPN). These findings, added to the fact that the supernatant as well as the "centrifuged medium" of the intact cells suspension displayed a fairly active O₂ consumption with malate as substrate in the presence of DPN and an electron carrier, indicate that the cell sap contains some DPN-linked malate dehydrogenase activity. The results suggest that the oxaloacetate-malate system might function as "shuttle" for the transfer of electrons from reduced diphosphopyridine nucleotide, generated in the cytoplasm, to the intramitochondrial electron transport chain of the tumor cells. -Ketoglutarate virtually failed to display any effect.

¹ This investigation was supported by Research Grant No. Ca-05271 of the National Cancer Institute, NIH, USPHS.

² Part of this study will be included in a thesis to be presented by Dalia Ram to the Hebrew University, in partial fulfilment of the requirements for the Ph.D. degree.

Received 3/10/66. Accepted 7/21/66.

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