Nitric Oxide Interactions with Mitochondrial Cytochrome c and Cytochrome Oxidase

P17 Vitamin E: From Chemistry to Biology - A REVIEW AND PERSPECTIVE Etsuo Niki, Human Stress Signal Research Center, Japan I was fascinated by the unique chemical structure of vitamin E (α-tocopherol) and started to study the kinetics and dynamics of its action as a radical scavenging antioxidant, aiming specifically at elucidating the effects of reaction milieu, that is, solution, membrane, lipoprotein, and in vivo. The effects of chroman ring methylation and side chain length were also studied. It was demonstrated that α-tocopherol acts as a potent radical scavenging antioxidant especially in combination with vitamin C. It has been often posed if the chemistry of vitamin E action observed in vitro can be applied to in vivo systems. Obviously, the capacity of vitamin E as an antioxidant in vivo is determined by many factors such as uptake, distribution, metabolism, and excretion in addition to chemical factors, but the kinetics and dynamics of its radical scavenging action may be same in vitro and in vivo. The efficacy of vitamin E for prevention of diseases may depend whether the oxidative stress induced by free radicals plays a causative role and vitamin E is present at the right time and right place and in right concentration. It is necessary to develop biomarkers which enable us to monitor and assess the preventive and/or treatment efficacy of vitamin E against diseases.

Etsuo Niki

doi:10.1016/j.freeradbiomed.2010.10.681

P18 NITRIC OXIDE Interactions with Mitochondrial Cytochrome c and Cytochrome Oxidase Chris Cooper1, Rebecca Holladay1, Peter Nicholls1, Dimitri Svistunenko1, Maria Mason1, Gary Silkstone1, and Mike Wilson1, 1University of Essex, UK NO• can interact with mammalian mitochondria under physiological and pathophysiological conditions. The highest affinity target is the oxygen-consuming enzyme, cytochrome c oxidase. This talk will review this interaction and suggest it can play a role in both NO• signalling and detoxification. It will contrast NO• effects with those of other cytochrome oxidase binding gasotransmitters such as CO and H2S. [1]. NO• has also been shown to interact with the substrate of cyotchrome oxidase, cytochrome c. NO can reversibly bind to both the reduced and oxidised states of cytochrome c. The binding affinity to the oxidised state is low (μM). The binding to the reduced state is of much higher affinity. At physiological pH the kinetics of association are limited by the dissociation of the heme methionine ligand, resulting in very low rates of binding. However, in the presence of cardiolipin the methionine ligand dissociates, allowing rapid high affinity binding of NO• [2]. In addition to reversible binding our previous studies showed that NO induces the oxidation of reduced cytochrome c, with the consequent production of nitroxyl anion. We now show that most of this oxidation is not caused by direct reactions of NO•, but instead by a reaction product of NO• and oxygen, most likely •NO2. We will discuss the molecular mechanism of these interactions and comment on their biological relevance. 1.) Cooper CE, Brown GC (2008) The inhibition of mitochondrial cytochrome oxidase by the gases carbon monoxide, nitric oxide, hydrogen cyanide and hydrogen sulfide: chemical mechanism and physiological significance. J. Bioenerg. Biomembr. 40:533-539. 2.) Silkstone G, Kapetanaki SM, Husu I, Vos MH, Wilson MT (2010) Nitric oxide binds to the proximal heme coordination site of the ferrocytochrome c/cardiolipin complex: formation mechanism and dynamics. J. Biol. Chem. 285:19785-19792. doi:10.1016/j.freeradbiomed.2010.10.682

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Chris Cooper