Biochemical and functional interaction between complex I and mtNOS

BOMBICINO SS; ZAOBORNYJ T; IGLESIAS DE; GELPI R,; BOVERIS A,; VALDEZ LB

Punta Ballena

Simposio; Thiol metabolism and redox regulation of cellular functions; 2011

Poderoso’s group (2006) showed that not only complex IV but also complex I proteins immunoprecipitate with mtNOS. The aim of this work was to study the functional interaction between complex I and mtNOS in: (a) a physiological situation, using beef heart inside-out particles (ETPH(Mg2+)); and (b) a pathological condition, using a rabbit myocardial stunning model. (1)ETPH(Mg2+) showed NAD+ reductase activity (17 nmol/min.mg protein) in the presence of succinate and ATP to establish reversal electron flow. This activity was inhibited by rotenone, mCCCP and oligomycin (94-98%). Bovine ETPH(Mg2+) produced NO at a rate of 0.83 nmol/min.mg protein. This activity was still detectable (77%) in the absence of an exogenous electron donor (NADPH). Rotenone inhibited mtNOS activity supported by reversal electron flow (90%), but it did not inhibit the activity of isolated nNOS. These data suggest that mtNOS could use electrons derived from complex I for its enzymatic activity. (2) In the myocardial stunning model, 15min-ischemia/30min-reperfusion selectively decreased malate-glutamate supported mitochondrial state 3 respiration (32%), and complex I and mtNOS activities (28%). The pattern observed for the decline of complex I activity was also observed for the reduction of mtNOS biochemical and functional activities, in accordance to the reported physical and functional interaction between complex I and mtNOS. This impairment was accompanied by an enhancement in malate-glutamate supported state 4 H2O2 production (78%), mitochondrial phospholipid oxidation products (42%) and proteins tyrosine nitration (50%), leading to a mitochondrial dysfunction named “complex I syndrome”. The results presented provide evidence about a functional interaction between complex I and mtNOS not only in physiological situations but also under pathological conditions.