Oxygen free radicals and iron in relation to biology and medicine: some problems and concepts.

Mammalian nitric oxide synthases.

An antioxidant is a substance that, when present at low concentrations compared to those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate. Many substances have been suggested to act as antioxidants in vivo, but few have been proved to do so. The present review addresses the criteria necessary to evaluate a proposed antioxidant activity. Simple methods for assessing the possibility of physiologically-feasible scavenging of important biological oxidants (superoxide, hydrogen peroxide, hydroxyl radical, hypochlorous acid, haem-associated ferryl species, radicals derived from activated phagocytes, and peroxyl radicals, both lipid-soluble and water-soluble) are presented, and the appropriate control experiments are described. Methods that may be used to gain evidence that a compound actually does function as an antioxidant in vivo are discussed. A review of the pro-oxidant and anti-oxidant properties of ascorbic acid that have been reported in the literature leads to the...

How to characterize a biological antioxidant.

Oxidative degradation of cell membrane lipids in the presence of molecular oxygen, a sensitizing agent and exciting light is termed photodynamic lipid peroxidation (photoperoxidation). Like other types of lipid peroxidation, photoperoxidation is detrimental to membrane structure and function, and could play a role in many of the toxic as well as therapeutic effects of photodynamic action. Recent advances in our understanding of photoperoxidation and its biomedical implications are reviewed in this article. Specific areas of interest include (a) reaction mechanisms; (b) methods of detection and quantitation; and (c) cellular defenses (enzymatic and non-enzymatic).

Photodynamic lipid peroxidation in biological systems

The nitric oxide (NO) synthase family of enzymes generate NO from L-arginine, which acts as a biologic effector molecule in a broad number of settings. This report summarizes some of the current information regarding NO synthase structure-function, reaction mechanism, control of catalysis, and protein interactions.

Superoxide radical from xanthine oxidase acting upon lumazine.

: The aerobic xanthine oxidase reaction causes the co-oxidation of 2,5- dimethylfuran to cis-diacetylethylene and the bleaching of rubrene tetracarboxylate. These actions were suppressed by superoxide dismutase, catalase, desferrioxamine andy by benzoate and other hydroxyl radical scavengers. The bleaching of rubrene tetracarboxylate was not enhanced in D2O. These result suggest OH, generated from 02(-) plus H202 by an iron-catalyzed Haber Weiss reaction, was the responsible agent and that singlet oxygen was not detectably involved. Control experiments, in which singlet oxygen was generated photochemically, demonstrated that replacement of H20 by D20 caused the expected enhancement of the chemical reactivity of singlet oxygen under the conditions of these experimental and that O2(-) at concentrations achieved by the xanthine oxidase reaction, did not detectably quench singlet oxygen. We conclude that singlet oxygen, if produced at all during the aerobic xanthine oxidase reaction, cannot exceed 0.1% of the production of O2(-).

Tetsuo Nagano

Papers

Superoxide radical from xanthine oxidase acting upon lumazine.

Does the Aerobic Xanthine Oxidase Reaction Generate Singlet Oxygen

The co-oxidation of ammonia to nitrite during the aerobic xanthine oxidase reaction.