Interaction between mitochondrial oxidative phosphorylation chain and a cationic derivative of azobenzene with photocontrollable structure

AzoTAB is a derivative of azobenzene containing tetraalkylammoniumcation. This compound can be used as an agent for photocontrol of cardiac cells excitability. Since the use of the substance is very perspective for a wide class of applications related to excitable cell cultures, we are interested in the study of the action of AzoTAB on the respiration chain of mitochondria, because the maintenance of normal homeostasis of excitable cells systems is directly connected with their energy state. It is demonstrated that trans-AzoTAB is an inhibitor of the mitochondrial respiratory chain which blocks both dehydrogenases- complex I and complex II. The affinity of trans-AzoTAB to NADHdehydrogenase is greater than the affinity to succinatedehydrogenase. This result completely corresponds to the theoretical preliminary expectations made in previous studies. The degree of respiration inhibition by trans-AzoTAB depends on which of dehydrogenases is the main electron supplier of the chain. But there is no difference between uncoupled and phosphorylating respirations. This is the evidence that trans-AzoTAB under experimental conditions (concentration 50-500 mkM) does not affect ATP-synthase activity. Also, it is demonstrated that cis-AzoTAB does not inhibit the respiratory chain. It increases uncoupled respiration (not phosphorylating) for both of substrates. We may interpret this phenomenon in two ways. First, cis-AzoTAB may be able to increase the lateral transfer of membrane bound protons which directly take part in the ATP synthesis by complex V. Second, the presence of cis-AzoTAB may cause mitochondrial swelling, which also leads to an increase in respiration rate in the third state.