Nicotinamide adenine dinucleotide, NAD⁺ and NADH is a redox cofactor localized in the electron transfer system. At the NADH-junction, dehydrogenases in the tricarboxylic acid cycle and mt-matrix dehydrogenases reduce NAD⁺ to NADH, the substrate of Complex I (CI). The mt-NADH pool integrates the reducing activity of the dehydrogenases upstream of CI with the oxidizing activity of electron transfer form CI into the Q-junction. Therefore the NADH-redox state is a metabolic marker.

The NextGen-O2k with the O2k-NADH-Module allows simultaneous measurement of oxygen consumption and NADH-redox state based on NADH autofluorescence. Importantly, this measurement does not distinguish between NADH and NADPH. Therefore, the measurement is more accurately related to the NAD(P)H-redox state. The O2k-NADH-Module and O2k-Q-Module extend high-resolution respirometry to advance state-of-the-art RedoxBiology.