Sulfide has the highest affinity to either the pulsed or partially reduced states of the enzyme, and is capable of partially reducing the enzyme at the heme a3 center. It is unclear whether endogenous H2S levels are sufficient to inhibit the enzyme. There is no interaction between hydrogen sulfide and the fully reduced conformation of COX.Methanol in methylated spirits is converted into formic acid, which also inhibits the same oxidase system. High levels of ATP can allosterically inhibit cytochrome c oxidase, binding from within the mitochondrial matrix. Extramitochondrial and subcellular localizations
Cytochrome c oxidase has 3 subunits which are encoded by mitochondrial DNA (cytochrome c oxidase subunit I, subunit II, and subunit III). Of these 3 subunits encoded by mitochondrial DNA, two have been identified in extramitochondrial locations. In pancreatic acinar tissue, these subunits were found in zymogen granules. Additionally, in the anterior pituitary, relatively high amounts of these subunits were found in growth hormone secretory granules. The extramitochondrial function of these cytochrome c oxidase subunits has not yet been characterized. Besides cytochrome c oxidase subunits, extramitochondrial localization has also been observed for large numbers of other mitochondrial proteins. This raises the possibility about existence of yet unidentified specific mechanisms for protein translocation from mitochondria to other cellular destinations. Genetic defects and disorders
Defects involving genetic mutations altering cytochrome c oxidase (COX) functionality or structure can result in severe, often fatal metabolic disorders. Such disorders usually manifest in early childhood and affect predominantly tissues with high energy demands (brain, heart, muscle).
Such brain mapping has been accomplished in spontaneous mutant mice with cerebellar disease such as reeler and a transgenic model of Alzheimers disease. This technique has also been used to map learning activity in the animal brain. Additional images
See also
Cytochrome c oxidase subunit I
Cytochrome c oxidase subunit II
Cytochrome c oxidase subunit III
Heme a

References
External links
The Cytochrome Oxidase home page at Rice University
Interactive Molecular model of cytochrome c oxidase (Requires MDL Chime)
UMich Orientation of Proteins in Membranes families/superfamily-4
Cytochrome-c+Oxidase at the US National Library of Medicine Medical Subject Headings (MeSH)