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Ignarro et al.:Formation of free nitric oxide from L-arginine by nitric oxide PDF Stampa E-mail
Monday 26 November 2007

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formation of free nitric oxide from L-arginine by nitric oxide

synthase: Direct enhancement of generation by

superoxide dismutase

chemiluminescence/nitroxyl/superoxide anion)

ADRIAN J. HOBBS, JON M. FUKUTO, AND Louis J. IGNARRO*

Department of Pharmacology, Center for the Health Sciences, University of California, School of Medicine, Los Angeles, CA 90024

Communicated by Charles H. Sawyer, June 30, 1994 (received for review December 6, 1993)

ABSTRACT Although nitric oxide (NO) appears to be one

of the oxidation products of L-arginine catalyzed by NO

synthase (NOS; EC 1.14.13.39), past studies on the measurement

of NO in cell-free, enzymatic assays have not been based

on the direct detection of the free NO molecule. Instead, assays

have relied on indirect measurements of the stable NO oxidation

products nitrite and nitrate and on indirect actions of NO

such as guanylate cyclase activation and oxyhemoglobin oxidation.

Utilizing a specific chemiluminescence assay, we report

here that the gaseous product of L-arginine oxidation, catalyzed

by both inducible macrophage and constitutive neuronal NOS,

is indistinguishable from authentic NO on the basis of their

physicochemical properties. NO gas formation by NOS was

dependent on L-arginine, NADPH, and oxygen and inhibited

by NG-methyl'L arginine and cyanide anion. Superoxide dismutase

(SOD) caused a marked, concentration-dependent increase

in the production of free NO by mechanisms that were

unrelated to the dismutation of superoxide anion or activation

of NOS. These observations indicate that free NO is formed as

a result of NOS-catalyzed L-ainine oxidation and that SOD

enhances the generation of NO without directly affecting NO

itself. SOD appears to elicit a novel biological action, perhaps

accelerating the conversion of an intermediate in the L-arginine-

NO pathway such as nitroxyl (HNO) to NO.

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