Effects of nitric oxide per sé on mitocondrial complex III. Functional consequences

BOMBICINO SS; BOVERIS A; IGLESIAS DE; VALDEZ LB

Buenos Aires

Congreso; Reunion Conjunta de Sociedades de Biociencia; 2017

SAIC, SAIB, SAI, SAA, SABiologia, SABiofisica, SAFE, SAFIS, SAH, SAP

At submicromolar concentrations, NO regulates mitochondrial respirationunder physiological conditions through two main effects onrespiratory chain: the competitive inhibition of complex IV with O2and the inhibition of electron transfer at complex III. Previous resultsfrom our laboratory showed that NO (~1.2 mM), released from S-nitrosoglutathioneor spermine-NONOate, inhibited complex II-III activity(50%) without changes in complex II activity, both measured insubmitochondrial particles (SMP) from bovine heart. This inhibitionlead to the accumulation of cytochrome b2+ (71%), independentlyon [O2], and it was not affected by HbO2 addition. NO produced theincrease of [UQH●]ss and, consequently, of O2●- and H2O2 productionrates (58%). In this work, experiments using NO solution, obtainedby bubbling of NO gas under N2 atmosphere, on complex IIIenriched mitochondrial fraction, obtained from bovine heart, wereperformed. Decylubiquinol:cytochrome c reductase activity wasinhibited (50%) by 1 mM NO, confirming the results obtained withNOdonors. The absorbance spectra of complex III enriched fractionexposed to NO showed the characteristic peak of cytochrome b2+at 562 nm. In coupled mitochondria, 1 mM NO inhibited state 3 O2consumption sustained by succinate (~50%). While 90% of the O2consumption was recovered by the addition of HbO2, the remaining10% was insensitive to NOscavenger addition, suggesting theblockage of complex III by NO. Moreover, mitochondria exposed toNO showed a less change in Δy (30%) in the transition from state4 to state 3 respiration, indicating a decrease in ATP synthesis capacity.Furthermore, H2O2 production rate was augmented (55%),according to the electron transfer inhibition and the [UQH●]ss enhancementdetected by EPR. Altogether, these results suggest thatthe interaction of NO with cytochrome b inhibits electron transfer atbc1 complex and stabilizes the UQH●, increasing O2●- and, as consequence,H2O2 productions.