The peroxidase and peroxynitrite reductase activity of human erythrocyte peroxiredoxin 2 |
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Authors: | Bruno Manta Martín Hugo Cecilia Ortiz Gerardo Ferrer-Sueta Madia Trujillo Ana Denicola |
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Institution: | a Laboratorio de Fisicoquímica Biológica, Instituto de Química Biológica, Facultad de Ciencias, Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay b Unidad de Biofísica de Proteínas, Instituto Pasteur de Montevideo, Montevideo, Uruguay c Departamento de Bioquímica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay d Center for Free Radical and Biomedical Research, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay |
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Abstract: | Peroxiredoxin 2 (Prx2) is a 2-Cys peroxiredoxin extremely abundant in the erythrocyte. The peroxidase activity was studied in a steady-state approach yielding an apparent KM of 2.4 μM for human thioredoxin and a very low KM for H2O2 (?0.7 μM). Rate constants for the reaction of peroxidatic cysteine with the peroxide substrate, H2O2 or peroxynitrite, were determined by competition kinetics, k2 = 1.0 × 108 and 1.4 × 107 M−1 s−1 at 25 °C and pH 7.4, respectively. Excess of both oxidants inactivated the enzyme by overoxidation and also tyrosine nitration and dityrosine were observed with peroxynitrite treatment. Prx2 associates into decamers (5 homodimers) and we estimated a dissociation constant Kd < 10−23 M4 which confirms the enzyme exists as a decamer in vivo. Our kinetic results indicate Prx2 is a key antioxidant enzyme for the erythrocyte and reveal red blood cells as active oxidant scrubbers in the bloodstream. |
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Keywords: | Peroxiredoxin Red blood cell Erythrocyte Peroxynitrite Hydrogen peroxide Overoxidation Oligomerization |
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