Determination of mitochondrial nitric oxide synthase activity.
The main biological targets of nitric oxide (NO) are hemoproteins, thiols, and superoxide anion (O2-). Mitochondria possess several hemoproteins, thiol-containing molecules, and they are one of the prime cellular producers of O2-. Thus, these organelles remain one of the main biological targets for NO. Reports on the existence of a Ca2+-sensitive mitochondrial NO synthase (mtNOS) have opened a new window in the field of NO and mitochondria research (Ghafourifar and Richter, 1997). mtNOS-derived NO reversibly decreases the activity of the mitochondrial hemoprotein, cytochrome c oxidase. This function of mtNOS regulates mitochondrial respiration and transmembrane potential (Deltapsi). The NO generated by mtNOS reacts with mitochondrial thiol-containing proteins including caspase-3. Because the S-nitrosated caspase-3 remains apoptotically silent as long as it is located within the mitochondria, this function of mtNOS portrays an anti-apoptotic property for mtNOS. mtNOS-derived NO also reacts with O2- to generate peroxynitrite. mtNOS-derived peroxynitrite induces oxidative stress and releases cytochrome c from the mitochondria, which represents a pro-apoptotic role for mtNOS. How mitochondria harmonize the reversible functions of mtNOS for mitochondrial respiration, its anti-apoptotic actions via S-nitrosation of caspase-3, versus the pro-apoptotic properties of peroxynitrite remains to be fully understood. However, intramitochondrial ionized Ca2+ concentration ([Ca2+]m) and the status of mitochondrial reducing defense barriers seem to play crucial roles in orchestrating the functions of mtNOS for mitochondria and cells (Ghafourifar and Cadenas, 2005).
Ghafourifar
Pedram
P
University of North Dakota, School of Medicine and Health Sciences, Grand Forks, North Dakota, 58202-9037, USA.
Asbury
Melinda L
ML
Joshi
Sandeep S
SS
Kincaid
Eric D
ED
D000818:Animals; D017209:Apoptosis; D004734:Energy Metabolism; D008928:Mitochondria / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D018384:Oxidative Stress; D013053:Spectrophotometry / Q000379:methods
D019001:Nitric Oxide Synthase