Tetrahydrobiopterin inhibits monomerization and is consumed during catalysis in neuronal NO synthase.
نویسندگان
چکیده
The biosynthesis of nitric oxide (NO) is catalyzed by homodimeric NO synthases (NOS). For unknown reasons, all NOS co-purify with substoichiometric amounts of (6R)-5,6,7,8-tetrahydrobiopterin (H(4)Bip) and require additional H(4)Bip for maximal activity. We examined the effects of H(4)Bip and pterin-derived inhibitors (anti-pterins) on purified neuronal NOS-I quaternary structure and H(4)Bip content. During L-arginine turnover, NOS-I dimers time dependently dissociated into inactive monomers, paralleled by a loss of enzyme-associated pterin. Dimer dissociation was inhibited when saturating levels of H(4)Bip were added during catalysis. Similar results were obtained with pterin-free NOS-I expressed in Escherichia coli. This stabilizing effect of H(4)Bip was mimicked by the anti-pterin 2-amino-4,6-dioxo-3,4,5,6,8,8a,9, 10-octahydro-oxazolo[1,2f]-pteridine (PHS-32), which also displaced NOS-associated H(4)Bip in a competitive manner. Surprisingly, H(4)Bip not only dissociated from NOS during catalysis, but was only partially recovered in the solute (50.0 +/- 16.5% of control at 20 min). NOS-associated H(4)Bip appeared to react with a NOS catalysis product to a derivative distinct from dihydrobiopterin or biopterin. Under identical conditions, reagent H(4)Bip was chemically stable and fully recovered (95.5 +/- 3.4% of control). A similar loss of both reagent and enzyme-bound H(4)Bip and dimer content was observed by NO generated from spermine NONOate. In conclusion, we propose a role for H(4)Bip as a dimer-stabilizing factor of neuronal NOS during catalysis, possibly by interfering with enzyme destabilizing products.
منابع مشابه
Enzymatic function of nitric oxide synthases.
Nitric oxide (NO) is synthesised from L-arginine by the enzyme NO synthase (NOS). The complex reaction involves the transfer of electrons from NADPH, via the flavins FAD and FMN in the carboxy-terminal reductase domain, to the haem in the amino-terminal oxygenase domain, where the substrate L-arginine is oxidised to L-citrulline and NO. The haem is essential for dimerisation as well as NO produ...
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ورودعنوان ژورنال:
- The Journal of biological chemistry
دوره 274 35 شماره
صفحات -
تاریخ انتشار 1999