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J. Biol. Chem., Vol. 280, Issue 10, 8850-8854, March 11, 2005

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Direct Measurement of Nitric Oxide and Oxygen Partitioning into Liposomes and Low Density Lipoprotein^*

Matías Möller¶, Horacio Botti¶||, Carlos Batthyany¶||, Homero Rubbo||**, Rafael Radi||, and Ana Denicola

From the Laboratorio de Fisicoquímica Biológica, Facultad de Ciencias, the ^||Departamento de Bioquímica, Facultad de Medicina, and the Center for Free Radical and Biomedical Research, Universidad de la República, 11400 Montevideo, Uruguay

Nitric oxide (·NO) has been proposed to play a relevant role in modulating oxidative reactions in lipophilic media like biomembranes and lipoproteins. Two factors that will regulate ·NO reactivity in the lipid milieu are its diffusion and solubility, but there is no data concerning the actual diffusion (D) and partition coefficients (K_P) of ·NO in biologically relevant hydrophobic phases. Herein, a "equilibrium-shift" method was designed to directly determine the ·NO and O₂ partition coefficients in liposomes and low density lipoprotein (LDL) relative to water. It was found that ·NO partitions 4.4- and 3.4-fold in liposomes and LDL, respectively, whereas O₂ behaves similarly with values of 3.9 and 2.9, respectively. In addition, actual diffusion coefficients in these hydrophobic phases were determined using fluorescence quenching and found that ·NO diffuses 2 times slower than O₂ in the core of LDL and 12 times slower than in buffer . The influence of ·NO and O₂ partitioning and diffusion in membranes and lipoproteins on ·NO reaction with lipid radicals and auto-oxidation is discussed. Particularly, the 3–4-fold increase in O₂ and ·NO concentration within biological hydrophobic phases provides quantitative support for the idea of an accelerated auto-oxidation of ·NO in lipid-containing structures, turning them into sites of enhanced local production of oxidant and nitrosating species.

Received for publication, December 6, 2004 , and in revised form, December 29, 2004.

^* This work was supported in part by Grant R03 TW001493 from the National Institutes of Health (to H. R. and A. D.) and grants from the Wellcome Trust and PDT (Uruguay) (to H. R.) and the Howard Hughes Medical Institute (to R. R.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ Partially supported by fellowships from Programa de Desarrollo de Ciencias Basicas and Comisión Sectional de Investigacion Cientifica (Uruguay).

^** A fellow of the John Simon Guggenheim Memorial Foundation.

An International Research Scholar of the Howard Hughes Medical Institute.

To whom correspondence should be addressed: Laboratorio de Fisicoquímica Biológica, Facultad de Ciencias, Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay. E-mail: denicola{at}fcien.edu.uy.

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