Biochem. J. (2009) 419
(411–418) (Printed in Great Britain)
Cytochrome P450 oxidoreductase participates in nitric oxide consumption by rat brain
Catherine N. HALL1,2, Robert G. KEYNES1 and John GARTHWAITE
Wolfson Institute for Biomedical Research, University College London, Gower Street, London WC1E 6BT, U.K.
In low nanomolar concentrations, NO (nitric oxide) functions as a transmitter in brain and other tissues, whereas near-micromolar NO concentrations are associated with toxicity and cell death. Control of the NO concentration, therefore, is critical for proper brain function, but, although its synthesis pathway is well-characterized, the major route of breakdown of NO in brain is unclear. Previous observations indicate that brain cells actively consume NO at a high rate. The mechanism of this consumption was pursued in the present study. NO consumption by a preparation of central glial cells was abolished by cell lysis and recovered by addition of NADPH. NADPH-dependent consumption of NO localized to cell membranes and was inhibited by proteinase K, indicating the involvement of a membrane-bound protein. Purification of this activity yielded CYPOR (cytochrome P450 oxidoreductase). Antibodies against CYPOR inhibited NO consumption by brain membranes and the amount of CYPOR in several cell types correlated with their rate of NO consumption. NO was also consumed by purified CYPOR but this activity was found to depend on the presence of the vitamin E analogue Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid), included in the buffer as a precaution against inadvertent NO consumption by lipid peroxidation. In contrast, NO consumption by brain membranes was independent of Trolox. Hence, it appears that, during the purification process, CYPOR becomes separated from a partner needed for NO consumption. Cytochrome P450 inhibitors inhibited NO consumption by brain membranes, making these proteins likely candidates.
Key words: brain, cytochrome P450 oxidoreductase (CYPOR), NADPH, nitric oxide.
Abbreviations used: CYPOR, cytochrome P450 oxidoreductase; DETA/NO, diethylenetriamine NONOate; DHEA, dehydroepiandrosterone; DPI, diphenyleneiodonium chloride; DTPA, diethylenetriaminepentaacetic acid; L-NNA, L-nitroarginine; NO, nitric oxide; NOGC, NO-activated guanylyl cyclase; NOS, NO synthase; SOD, superoxide dismutase; Trolox, 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid.
1These authors contributed equally to this work.
2To whom correspondence should be addressed (email catherine.hall@ucl.ac.uk).
Received 19 December 2008/16 January 2009; accepted 20 January 2009
Published as BJ Immediate Publication 20 January 2009, doi:10.1042/BJ20082419
© 2009 The Author(s)
The author(s) has paid for this article to be freely available under the terms of the Creative Commons Attribution Non-Commercial Licence (http://creativecommons.org/licenses/by-nc/2.5/) which permits unrestricted non-commercial use, distribution and reproduction in any medium, provided the original work is properly cited.
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