The Q-redox state reflects the redox state of Coenzyme Q (CoQ, ubiquinone and plastoquinone) in the mitochondrial or chloroplast electron transfer system ETS. Q represents these mobile redox components located centrally at the Q-junction of the mitochondrial respiratory ETS and the chloroplast photosynthesis system.

In mitochondria, the Q-redox state depends on the balance between reducing capacities of convergent electron entries from fuel substrates into the Q-junction and oxidative capacities downstream of Q with the final electron acceptor oxygen. Therefore, deficiencies in the mitochondrial ETS, originating from e.g. the malfunction of respiratory Complexes, can be diagnosed more precisely when combining respiratory measurements with continuous monitoring of the Q-redox state.

The O2k-Q-Module of the NextGen-O2k has been developed for measuring the Q redox state simultaneously with respiration in isolated mitochondria and chloroplasts, permeabilized cells, and animal and plant tissues. The O2k-Q-Module and the O2k-NADH-Module extend high-resolution respirometry to advance state-of-the-art RedoxBiology.