Abstract

A number of enzymes, reduced and oxidized levels of pyridine nucleotides, DNA, and protein have been measured in normal mammary gland and spontaneous, pregnancydependent and -independent mammary tumors from BR6 mice. Pregnancy-dependent tumors differed from pregnancy-independent tumors in having lower protein content, lower lactate dehydrogenase activity, and lower levels of nicotinamide adenine dinucleotide. These differences were unrelated to growth rate. Regression of dependent tumors was accompanied by rapid loss of DNA without reduction in enzyme concentration. Pregnancy-independent tumors from lactating animals showed only slight responsiveness to these conditions. Tumors differed from normal mammary gland in having low activities of glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, and phosphohexose isomerase, and low levels of NAD + ; total NADP was not changed, but the ratio NADP + : NADPH was increased. Tumor-bearing mice were found to have subnormal levels of NAD + in their livers.