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CO binding studies of nitric oxide synthase: effects of the substrate, inhibitors and tetrahydrobiopterin
Author(s) -
Sato Hideaki,
Nomura Susumu,
Sagami Ikuko,
Ito Osamu,
Daff Simon,
Shimizu Toru
Publication year - 1998
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(98)00699-1
Subject(s) - tetrahydrobiopterin , nitric oxide synthase , chemistry , nitric oxide , substrate (aquarium) , biochemistry , atp synthase , enzyme , pharmacology , medicine , biology , organic chemistry , ecology
The dissociation constant ( K d ) for CO from neuronal nitric oxide synthase heme in the absence of the substrate and cofactor was less than 10 −3 μM. In the presence of l ‐Arg, it dramatically increased up to 1 μM. In the presence of inhibitors such as N G ‐nitro‐ l ‐arginine methyl ester and 7‐nitroindazole (NI), the K d value further increased up to more than 100 μM. Addition of the cofactor, 5,6,7,8‐tetrahydrobiopterin (H 4 B), increased the K d value by 10‐fold in the presence of l ‐Arg, whereas it decreased the value to less than one 250th in the presence of NI. Addition of H 4 B increased the recombination rate constant ( k on ) for CO by more than two‐fold in the presence of l ‐Arg or N 6 ‐(1‐iminoethyl)‐ l ‐lysine, whereas it decreased the k on value by three‐fold in the presence of l ‐thiocitrulline. Thus, the binding fashion of some of inhibitors, such as NI, may be different from that of l ‐Arg with respect to the H 4 B effect.