J Bioenerg Biomembr (2007) 39:158–166 DOI 10.1007/s10863-007-9074-1 ORIGINAL PAPER Nitric oxide increases oxidative phosphorylation efficiency Pascaline Clerc · Michel Rigoulet · Xavier Leverve · Eric Fontaine Received: 23 January 2007 / Accepted: 8 March 2007 / Published online: 20 April 2007 C  Springer Science+Business Media, LLC 2007 Abstract We have studied the effect of nitric oxide (NO) and potassium cyanide (KCN) on oxidative phosphorylation efficiency. Concentrations of NO or KCN that decrease resting oxygen consumption by 10–20% increased oxidative phosphorylation efficiency in mitochondria oxidizing succinate or palmitoyl-l-carnitine, but not in mitochondria oxidizing malate plus glutamate. When compared to malate plus glutamate, succinate or palmitoyl-l-carnitine reduced the redox state of cytochrome oxidase. The relationship between membrane potential and oxygen consumption rates was measured at different degrees of ATP synthesis. The use of malate plus glutamate instead of succinate (that changes the H + /2e − stoichiometry of the respiratory chain) affected the relationship, whereas a change in membrane permeabil- ity did not affect it. NO or KCN also affected the relationship, suggesting that they change the H + /2e − stoichiometry of the respiratory chain. We propose that NO may be a natural short- term regulator of mitochondrial physiology that increases oxidative phosphorylation efficiency in a redox-sensitive manner by decreasing the slipping in the proton pumps. P. Clerc . X. Leverve . E. Fontaine INSERM, U884, F-38041, Grenoble, France P. Clerc . X. Leverve . E. Fontaine Universit´ e Joseph Fourier, Laboratoire de Bio´ energ´ etique Foundamentale et Appliqu´ ee, F-38041, Grenoble, France M. Rigoulet Institut de Biochimie et de G´ enetique Cellulaires du CNRS, Universit´ e Bordeaux II, Bordeaux, France E. Fontaine () INSERM, U884, F-38041, Grenoble, France, and Laboratoire de Bio´ energ´ etique Fondamentale et Appliqu´ ee, Universit´ e Joseph Fourier, BP 53, F-38041 Grenoble Cedex, France e-mail: eric.fontaine@ujf-grenoble.fr Keywords Mitochondria . Nitric oxide . Cyanide . Slipping . Leak . Oxidative phosphorylation Abbreviations NO: Nitric oxide . DPTA-NONOate: dipropylenetriamine-NONOate . EDTA: ethylene-diaminetetraacetic acid . DNP: 2,4-dinitrophenol . Pi: inorganic phosphate Introduction Mitochondrial respiration is characterized by the complete reduction of molecular oxygen to water. This process in- volves the generation of electrons from NADH or FADH 2 , which are produced by the oxidation of respiratory sub- strates. Electrons from NADH and FADH 2 pass through the respiratory chain and are finally accepted by oxygen, releasing energy that is stored in the form of an electrochem- ical proton gradient across a membrane. The transmembrane movement of protons back into mitochondria through the ATP-synthase then results in the production of ATP from ADP plus phosphate. The apparent yield of oxidative phos- phorylation (i.e., the ATP synthesis rate divided by the oxy- gen consumption rate) is, however, not constant, but changes according to (i) the respiratory substrates, (ii) the proton gradient-consuming processes that are not linked to ATP syn- thesis, and (iii) the intrinsic coupling (the H + /2e − stoichiom- etry) of the proton pumps (Murphy, 1989; Kadenbach, 2003). Because electrons from NADH pass through three proton pumps (namely, complexes I, III and IV), while electrons from FADH 2 only pass through two proton pumps (i.e., com- plexes III and IV), NADH-linked substrates (e.g., malate) generate more proton gradient per oxygen consumed than FADH 2 -linked substrates (e.g., succinate). Consequently, the yield of oxidative phosphorylation is higher with NADH- than FADH 2 -linked substrates (Hinkle, 2005). Springer