Figure 7. Schematic summary of the altered ROS metabolism in skeletal muscle fibres of nNOS-knockout-mice.

Under wild-type conditions (e.g. in C57 control mice), nitric oxide (NO) acts in skeletal muscle fibres as paracrine and autocrine signalling molecule but also might react with superoxide (O₂⁻) to generate peroxynitrite (ONOO⁻). Scavenging of superoxide is furthermore achieved by enzymatic catalysis of superoxide dismutases (e.g. the cytosolic SOD1) to yield hydrogen peroxide (H₂O₂), which is subsequently reduced to water by catalase, glutathione peroxidase or peroxiredoxin-6 activity. In nNOS-knockout mice, up-regulated SOD1 and peroxiredoxin-6 enable the scavenging of higher superoxide levels. Other proteins with impact on the ROS metabolism that were found to be up-regulated in skeletal muscle fibres of nNOS-knockout mice in the 2D-PAGE analysis (prohibitin, peroxiredoxin-3, HSP25 and NDP kinase B) are not included in the scheme. Grey down-toning or gradation of reactions or enzymes, respectively, indicates their absence or down-regulation. For further details, see Discussion.