Sandbox 5: Difference between revisions
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== | ==H4B== | ||
H4B is a cofactor. NOS contains two molecules of H4B, one in each monomer. The active center forms a kind of tunnel, because of the dimeric structure. This gives H4B the opportunity to play a big role in the control of subunit interactions and active-center formation. H4B therefor i s more of a structurel cofactor, in that it keeps the dimer stabilized by integration in to the hydrophobic parts of the dimer. Here it helps substrate interactions by lining the active-center channel and hydrogen bonding to the heme propionate amd to alfa7 which is two elements involved in L-Arg binding. So H4B is not the molecule that hydroxylates the substrate (L-Arg) nor activating the hemebound oxygen. | |||
Pterin induces some changes in the heme invironment, including ordering of the active -center channel, increased sequestration (sequestration (om proces) the action of forming a chelate or other stable compound with an ion or atom or molecule so that it is no longer available for reactions) of the heme ligand Cys194, and extension of the negative hemeA propionate away from the distal heme pocket may account for the 50mV increase in heme redox potential and low-high spin shift of the ferric heme iron in the presence og H4B. It also may increase the oxygen activation, because of the pterin-induced 70-fold increase in autoxidation of the ferrous heme-dioxy complex. | |||
Fra artiklen: structure of NOS oxygenase dimer with pterin and substrate))) | |||
and | |||
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