The relative effectiveness of human plasma glutathione peroxidase as a catalyst for the reduction of hydroperoxides by glutathione |
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Authors: | Sylvia A. Howard Wayne C. Hawkes |
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Affiliation: | (1) US Department of Agriculture, Agricultural Research Service, Western Human Nutrition Research Center, Building 1110, Presidio, P.O.Box 29997, 94129 San Francisco, CA |
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Abstract: | To reveal clues to the function of human plasma glutathione peroxidase (GPx), we investigated its catalytic effectiveness with a variety of hydroperoxides. Comparisons of hydroperoxides as substrates for plasma GPx based on the ratio ofV max /K m were blocked by the limited solubility of the organic hydroperoxides, which prevented kinetic saturation of the enzyme at the chosen glutathione concentration. Therefore, we compared the hydroperoxides by the fold increase in the apparent first-order rate constants of their reactions with glutathione owing to catalysis by plasma GPx. The reductions of aromatic and small hydrophobic hydroperoxides (cumene hydroperoxide,t-amyl hydroperoxide,t-butyl hydroperoxide, paramenthane hydroperoxide) were better catalyzed by plasma GPx than were reductions of the more “physiological” substrates (linoleic acid hydroperoxide, hydrogen peroxide, peroxidized plasma lipids, and oxidized cholesterol). |
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Keywords: | Plasma glutathione peroxidase extracellular glutathione peroxidase hydroperoxide substrate preference enzyme function |
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