Nitric oxide: a radical molecule in quest of free radicals in proteins |
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Authors: | O Guittet B Roy M Lepoivre |
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Institution: | (1) Unité 8619, Centre National de la Recherche Scientifique, Batiment 430, Université Paris-Sud, F-91405 Orsay (France), Fax +33 1 6985 3715, e-mail: michel.lepoivre@bbmpc.u-psud.fr, FR |
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Abstract: | A number of enzymes use an amino acid free radical cofactor. Tyrosyl and tryptophanyl radicals react with nitric oxide (NO)
with an almost diffusion-limited rate. The catalytically competent tyrosyl radical in ribonucleotide reductase (RR) and prostaglandin
H synthase (PGHS) recombines with NO in a radical-radical reaction. The unstable adduct formed can dissociate to regenerate
the tyrosyl radical. However, upon prolonged incubation with NO, the diiron center of mouse RR leaks out, while the adduct
is sucessively oxidized into an iminoxyl radical and a nitrotyrosine in PGHS. These data provide a plausible mechanism for
the physiological inactivation of RR observed in various models, and may help in understanding the inhibition of PGHS reported
in some cases. Reversible combination with NO is an intrinsic property of tyrosyl radicals, which also occurs with YD
• and YZ
• in photosystem II, where NO has been useful in the analysis of the oxygen-evolving complex. |
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Keywords: | , Nitric oxide, tyrosyl radical, radicals, nitrosotyrosine, nitrotyrosine, ribonucleotide reductase, prostaglandin,,,,,H synthase, photosystem II, |
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