Nitric Oxide Synthase: Difference between revisions
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===H<sub>4</sub>B=== | ===H<sub>4</sub>B=== | ||
[[image:bh4.png|left|frame|Structure of tetrahydrobiopterin]] | [[image:bh4.png|left|frame|Structure of tetrahydrobiopterin]] | ||
<scene name='Sandbox_5/Nos_oxygenase_bh4/11'>H4B</scene> is an essential cofactor in NOS and in the [[aromatic amino acid hydroxylases]]. NOS contains two molecules of <scene name='Sandbox_5/Begge_h4b/1'>H4B</scene>, one in each monomer. The active site forms part of the cavity already described. This cavity can be visualized as a <scene name='Nitric_oxide_synthase/Substratebinding_distal_pocket/2'>tunnel</scene>. Here H<sub>4</sub>B helps substrate interactions by lining the active-center tunnel and hydrogen bonding to the heme propionate and to alfa helix 7. The propionate group and alpha helix 7 are also involved in the L-Arg binding. This gives H<sub>4</sub>B the opportunity to play an important role in the control of subunit interactions and active site formation. H<sub>4</sub>B is therefore more or less a structural cofactor and has a stabilizing effect. Its structural importance is further reconned to play a role in dimer formation (dimerization requires bound zinc ion along with H<sub>4</sub>B), and major conformational changes leading to the formation of the active site channelform<ref name="Raman">PMID:9875848</ref>. | <scene name='Sandbox_5/Nos_oxygenase_bh4/11'>H4B</scene> is an essential cofactor in NOS and in the [[aromatic amino acid hydroxylases]]. NOS contains two molecules of <scene name='Sandbox_5/Begge_h4b/1'>H4B</scene>, one in each monomer. The active site forms part of the cavity already described. This cavity can be visualized as a <scene name='Nitric_oxide_synthase/Substratebinding_distal_pocket/2'>tunnel</scene>. Here H<sub>4</sub>B helps substrate interactions by lining the active-center tunnel and hydrogen bonding to the heme propionate and to alfa helix 7. The propionate group and alpha helix 7 are also involved in the L-Arg binding. This gives H<sub>4</sub>B the opportunity to play an important role in the control of subunit interactions and active site formation. H<sub>4</sub>B is therefore more or less a structural cofactor and has a stabilizing effect. Its structural importance is further reconned to play a role in dimer formation (dimerization requires bound zinc ion along with H<sub>4</sub>B), and major conformational changes leading to the formation of the active site channelform<ref name="Raman">PMID:9875848</ref>. | ||
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== Additional 3D Structures of Nitric Oxide Synthase == | == Additional 3D Structures of Nitric Oxide Synthase == | ||
''Update June 2011'' | |||
'''Nitric Oxide Synthase''' (NOS) is an enzyme which catalyzes the production of the signaling molecule NO from arginine. In mammals, NOS appears as 3 isozymes: neuronal NOS (nNOS), cytokine-inducible NOS (iNOS) and endothelial NOS (eNOS). The N-terminal domain of NOS is an oxygenase domain (OD). NOS cofactors are: NADPH, FAD, FMN, heme and O2. <br /> | '''Nitric Oxide Synthase''' (NOS) is an enzyme which catalyzes the production of the signaling molecule NO from arginine. In mammals, NOS appears as 3 isozymes: neuronal NOS (nNOS), cytokine-inducible NOS (iNOS) and endothelial NOS (eNOS). The N-terminal domain of NOS is an oxygenase domain (OD). NOS cofactors are: NADPH, FAD, FMN, heme and O2. <br /> | ||
