Abstract
Changes in cellular pyridine nucleotide and flavoprotein oxidation-reduction states associated with mixed-function oxidation of p-nitroanisole, hexobarbital and aminopyrine by perfused rat livers were studied. Surface fluorescence techniques were compared with NAD(P) +/NAD(P)H ratios calculated from substrates assumed to be in near equilibrium with various dehydrogenases in freeze-clamped liver samples. p-Nitroanisole and p-nitrophenol caused a large decrease in pyridine nucleotide (366 → 450 nm) fluorescence as a result of fluorescence quenching. This decrease, therefore, did not reflect oxidation of pyridine nucleotides. Moreover, p-nitroanisole infusion decreased the free NADP +:NADPH ratios calculated from malic enzyme and isocitrate dehydrogenase. Hexobarbital, which did not produce fluorescence quenching, caused an oxidation in pyridine nucleotides as indicated by both a decrease in surface fluorescence and an increase in the calculated NADP +/NADPH ratio. These data indicate that free NADP +/NADPH ratios calculated from substrates, which are assumed to be in near equilibrium with NADPH-generating enzymes, indeed reflect the NADPH redox state in intact liver cells.
Published Version
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