Biochemical Issues in Estimation of Cytosolic Free NAD-NADH RatioReportar como inadecuado

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Cytosolic free NAD-NADH ratio is fundamentally important in maintaining cellular redox homeostasis but current techniques cannot distinguish between protein-bound and free NAD-NADH. Williamson et al reported a method to estimate this ratio by cytosolic lactate-pyruvate L-P based on the principle of chemical equilibrium. Numerous studies used L-P ratio to estimate the cytosolic free NAD-NADH ratio by assuming that the conversion in cells was at near-equilibrium but not verifying how near it was. In addition, it seems accepted that cytosolic free NAD-NADH ratio was a dependent variable responding to the change of L-P ratio. In this study, we show 1 that the change of lactate-glucose percentage of glucose that converts to lactate by cells and L-P ratio could measure the status of conversion between pyruvate + NADH and lactate + NAD that tends to or gets away from equilibrium; 2 that cytosolic free NAD-NADH could be accurately estimated by L-P only when the conversion is at or very close to equilibrium otherwise a calculation error by one order of magnitude could be introduced; 3 that cytosolic free NAD-NADH is stable and L-P is highly labile, that the highly labile L-P is crucial to maintain the homeostasis of NAD-NADH; 4 that cytosolic free NAD-NADH is dependent on oxygen levels. Our study resolved the key issues regarding accurate estimation of cytosolic free NAD-NADH ratio and the relationship between NAD-NADH and L-P.

Autor: Feifei Sun , Chunyan Dai , Jiansheng Xie, Xun Hu



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