Cytochrome P450 oxidoreductase participates in nitric oxide consumption by rat brain

Abstract

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.

From synaptically localized to volume transmission by nitric oxide

“…The mechanism remains unclear, although cytochrome P450 oxidoreductase is a putative participant (Hall et al . ). At the level of the single synapse, an NO half‐life even as short as 5 ms would have very little effect on the local distribution of NO (Fig.…”

Nitric-oxide Dioxygenase Function of Human Cytoglobin with Cellular Reductants and in Rat Hepatocytes

“…Investigations of the NOD activities of Cygb, Ngb, and Mb with ascorbate reveal a uniquely efficient redox coupling with Cygb that may be attributed to a unique Cygb structure. In addition, we report that the Cygb-NOD activity is physically and kinetically distinct from the microsomal NOD activity (23,26,27).…”

Inhibition of nitric oxide‐activated guanylyl cyclase by calmodulin antagonists

“…NO inactivation under experimental conditions can result from numerous mechanisms, including generation of superoxide by buffers, reaction with cellular haemoproteins, reaction with cytochrome P450 and reaction with lipid peroxyl radicals (Martin et al, 1985;Crow and Beckman, 1995; Keynes et al, 2003;2005;Hall et al, 2009). The latter mechanism has been found to predominate in cell suspensions and homogenates under the conditions adopted in this study (Keynes et al, 2005).…”