Malic enzyme and malate dehydrogenase activities in rat tracheal epithelial cells during the progression of neoplasia.

Malic enzyme and malate dehydrogenase (MDH) activities were radiometrically assayed in digitonin fractionated normal primary cultures (NPC), preneoplastic selected primary cultures (SPC) and tumor-derived primary cultures (TPC) of rat tracheal epithelial cells. Carcinogen-altered SPC and TPC selectively grow in the absence of pyruvate, which is required by NPC for survival. Mitochondrial-containing particulate fractions from TPC and especially SPC had markedly higher levels of NADP+-dependent malic enzyme than NPC in the presence or absence of pyruvate. This suggests that induction of mitochondrial malic enzyme activity occurs early in the progression of neoplasia. Malic enzyme activities in the soluble fractions from the various populations were not distinctly different. In contrast, particulate-bound MDH activity was higher in NPC and SPC than TPC in most cases, indicating a decrease in this enzyme late in tumorigenesis.