Pyridine nucleotide-linked dehydrogenases and isozymes of normal rat breast and growing and regressing breast cancers.

Four pyridine nucleotide-linked dehydrogenases, glucose-6phosphate dehydrogenase (G6PDH),3 isocitric dehydrogenase (ICDH), lactic dehydrogenase (LDH), and malic dehydrogenase (MDH), and their isozymes have been studied in the normal virgin rat breast, in the breast of tumor-bearing rats, in the breast cancers themselves, and in these tissues following ovariectomy. Enzyme activity expressed per mg DNA-P facilitates compari son of tumor and normal cells. In breast cancer, the total LDH and G6PDH activity increased, MDH activity decreased, and the proportions of LDH and MDH isozymes were altered. The Kaplan M type of LDH isozyme (2) is more prominent in tu mors. Ovariectomy resulted in regression of tumor size accom panied by decrease in total G6PDH and LDH activity but did not restore to normal the proportions of LDH or MDH isozymes.