Functional activity of mitochondrial nitric oxide synthase

VALDEZ LB; ZAOBORNYJ T; BOVERIS A

Alba, Italia

Congreso; Joint Meeting of the Oxygen Club of California and the University of Torino, Oxidants and Antioxidants in Biology.; 2005

Oxygen Club of California

Nitric oxide added exogenously or produced by mitochondrial nitric oxide synthase (mtNOS) regulates mitochondrial electron transfer. The ability of mtNOS activity to modulate O2 uptake and H2O2 production has been named "functional activity of mtNOS”. Respiratory rates and H2O2 release were determined at maximal and minimal NO levels. Supplementation of state 3 mitochondria with L-arg and SOD decreased the respiration rate by 2-16%, whereas the addition of a NOS inhibitor and HbO2, increased the O2 consumption by 8-55% in heart, liver, kidney and brain mitochondria. These effects are explained by the inhibition of cytochrome oxidase by NO in a process that is competitive with O2 (Antunes et al., PNAS 48:16774-9, 2004). The difference between the state 3 O2 uptake with L-arg and SOD and with a NOS inhibitor and HbO2 indicates the mtNOS functional activity in the inhibition of cytochrome oxidase activity (13-70%). Addition of L-arg increased state 4 H2O2 production by 9-28% in heart, liver, kidney and brain mitochondria, whereas the supplementation with a NOS inhibitor decreased H2O2 generation by 3-55%. The difference in H2O2 production between the conditions of maximal and minimal NO levels is termed functional activity of mtNOS on the regulation H2O2 production (18-68%). The effects on H2O2 production are explained by the NO inhibition of ubiquinol-succinate-cytochrome c reductase activity that enhances H2O2 production. The regulatory role of NO on mitochondrial functions extends from physiological to pathological situations. Simple respiratory determinations such as O2 consumption and H2O2 production can be effectively used to assay effects of physiological or pharmacological treatments on mtNOS activity and mitochondrial function.