© 2003 Annual ReviewsAll images redrawn from D. Boehning, S.H. Snyder, Ann Rev Neurosci, 26:105–31, 2003.
Neuronal nitric oxide synthase (nNOS) is localized to NMDA receptors by the PDZ-domain adaptor protein PSD95. Calcium entry activates nNOS by a calcium/calmodulin-dependent mechanism. NO can diffuse to neighboring cells to activate soluble guanylyl cyclase or to nitrosylate cysteine residues on target proteins. Nitrosylation inhibits NMDA receptors providing a negative feedback loop. CAPON competes with PSD95 for nNOS to facilitate the nitrosylation and subsequent activation of Dexras1.
High levels of carbon monoxide interfere with cellular respiration and pollute the environment. Hydrogen sulfide (H2S), another chemical asphyxiant, paralyzes the sense of smell and at lower levels produces the rotten-egg stink prized by children using their first chemistry sets. But even the noxious to the downright deadly can have a subtler side: at minute concentrations, both gases transmit biological signals between cells.
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