The state 4/state 3 transition regulates mitochondrial nitric oxide synthase activity

ZAOBORNYJ T; VALDEZ LB; BOVERIS A

Buenos Aires, Argentina

Congreso; XIIth Meeting of the Society for Free Radical Research International; 2004

Society for Free Radical Research International

Mitochondrial nitric oxide synthase (mtNOS) was found to be a highly regulated enzyme; that in turn, plays a regulatory role. This work shows the dependence of NO production with mitochondrial metabolic state. The mtNOS activity at pH 7.4 in liver and kidney submitochondrial membranes was 1.3±0.2 and 0.86±0.05 nmol/min.mg protein, respectively. NO production in cytosol at the same pH was 50% lower than in the mitochondrial fraction. Liver and kidney mitochondria contribute with 37% and 30% of the total cellular NO production. The state 4/state 3 transition regulates mtNOS activity and NO release in coupled mitochondria. NO production by liver mitochondria, were 1.4±0.2 and 0.70±0.05 nmol NO/min.mg protein, in state 4 and 3 respectively. NO production by kidney mitochondria, were 0.70±0.05 and 0.40±0.05 nmol NO/min.mg protein, in state 4 and 3 respectively. As a whole, NO production rates at state 3 were 40-50% lower than at state 4. Addition of Ca2+ increased the rate of NO production indicating that intramitochondrial Ca2+ is able to regulate mtNOS actitity. At present, the determination of similar specific activities for the mtNOS of mitochondria isolated from a series of organs, the sequencing of liver mtNOS, and the dependence of mtNOS activity on the mitochondrial metabolic state, establishes mtNOS as an integral protein of the inner mitochondrial membrane and a likely regulator of mitochondrial functions.