Aerobic glycolysis in homogenates of normal and tumor tissues.

Previous investigations from this laboratory have revealed that the over-all oxidative capacity of tumor tissues, in general, falls in the range of the less active normal tissues and at a level much lower than normal liver, kidney, heart, or brain (12), while the enzymes of the glycolytic system occur in quantities of the same order of magnitude in all these tissues (5, 6). Since the conclusions regarding oxidative capacity have been questioned (19), further studies with systems not previously em ployed are here reported. In earlier studies on the malic dehydrogenase system (10, 16), information was obtained con cerning the DPN'-cytochrome c reducÃ-asecontent of various tissues. This was done by adding a crude preparation of malic dehydrogenase that con tained no cytochrome reductase to a homogenate, with the result that the rate-limiting reaction was the reduction of cytochrome c and that the meas urement of oxygen uptake could be taken as an assay of the DPN-cytochrome c reductase when DPN and cytochrome c were added in excess. The data showed that in liver homogenates the cyto chrome c reductase was present in excess, and it was concluded that, in the absence of added malic dehydrogenase, the rate of oxygen uptake was a measure of the latter enzyme in the homogenate. However, in primary rat hepatomas there was such a narrow margin between the two enzymes that it could not be assumed that either enzyme was lim iting in the unsupplemented homogenate (10, p. 317). More recent work by Weinhouse et al. (21, 22) has indicated that the malic dehydrogenase component is not low in tumor tissue, and this ob servation suggests that the cytochrome reductase was limiting even in the measurements carried out without a malic dehydrogenase supplement. These studies yielded Qo, values of 103.5 and 15.1, re spectively, for liver and hepatoma (10). Reaction mixtures for the study of glycolysis in