1. A new method has been developed for measuring the total antioxidant capacity of body fluids and drug solutions, based on the absorbance of the ABTS.+ radical cation. 2. An automated method for use on a centrifugal analyser, as well as a manual method, is described. 3. The procedure has been applied to physiological antioxidant compounds and radical-scavenging drugs, and an antioxidant ranking was established based on their reactivity relative to a 1.0 mmol/l Trolox standard. 4. The Trolox equivalent antioxidant capacity of plasma from an adult reference population has been measured, and the method optimized and validated. 5. The method has been applied to investigate the total plasma antioxidant capacity of neonates and how this may be compromised in prematurity.

A Novel Method for Measuring Antioxidant Capacity and its Application to Monitoring the Antioxidant Status in Premature Neonates

The hydrophilic and lipophilic contribution to total antioxidant activity

DNA-enhanced peroxidase activity of a DNA aptamer-hemin complex

A comparative study has been performed with several fungal laccases for the oxidation of a series of phenols, anilines, and benzenethiols and for the inhibition by halides. The observed Km and kcat were correlated to the structure of substrate. The change in log (kcat/Km) was found to be proportional to the one-electron redox potential difference between laccase's type 1 copper site and substrate. This correlation indicated that the first electron transfer from substrate to laccase was governed by the “outer-sphere” mechanism. Compared to the electronic factor, the steric effect of small o-substituents (such as methyl and methoxy groups) was found to be unimportant. The depth of the laccase's type 1 copper site was estimated as ∼10 A by comparing the steric effect among five 2-methoxyphenols whose 4-substituents ranged from 0.1 to 14 kDa in mass. The observed inhibition potency order of F- > Cl- > Br- was attributed to limited accessibility of laccase's type 2/type 3 trinuclear copper cluster site. Althou...

Oxidation of phenols, anilines, and benzenethiols by fungal laccases: correlation between activity and redox potentials as well as halide inhibition.

A study of a series of recombinant fungal laccases and bilirubin oxidase that exhibit significant differences in redox potential, substrate specificity, and stability

The chemical nature of the important new chromogen ABTS [2,2'-azino-di-(3-ethyl-benzthiazoline-6-sulphonic acid)] is described together with an account of the redox and spectroscopic properties of the system ABTS--H2O2--peroxidase. Keq. is calculated and a study of the steady-state kinetics over a whole range of substrate concentrations is reported. By using novel methods of kinetic analysis, an interpretation of the results is given which requires some extension of the classical peroxidase mechanism.

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W G Bardsley

Papers

The steady-state kinetics of peroxidase with 2,2′-azino-di-(3-ethyl-benzthiazoline-6-sulphonic acid) as chromogen