Mitochondrial metabolic states and membrane potential modulate mtNOS activity

VALDEZ LB; ZAOBORNYJ T; BOVERIS A

Biochim Biophys Acta

Elsevier

Año: 2006 vol. 1757 p. 166 - 172

The mitochondrial metabolic state regulates the rate of NO release from coupled mitochondria: NO release by heart, liver and kidney mitochondria was about 40-45% lower in state 3 (1.2, 0.7 and 0.4 nmol/min.mg protein) than in state 4 (2.2, 1.3 and 0.7 nmol/min.mg protein). The activity of mtNOS, responsible for NO release, appears driven by the membrane potential component and not by intramitochondrial pH of the proton motive force. The intramitochondrial concentrations of the NOS substrates, L-arginine (about 310 mM) and NADPH (1.04-1.78 mM) are 60-1000 times higher than their KM values. Moreover, the changes in their concentrations in the state 4-state 3 transition are not enough to explain the changes in NO release. Nitric oxide release was exponentially dependent on membrane potential as reported for mitochondrial H2O2 production (Korshunov et al., 1997). Agents that decrease or abolish membrane potential, minimize NO release while the addition of oligomycin that produces mitochondrial hyperpolarization generates the maximal NO release. The regulation of mtNOS activity, an apparently voltage-dependent enzyme, by membrane potential is marked at the physiological range of membrane potentials.