Flavin-mediated photoinactivation of spinach leaf nitrate reductase involving superoxide radical and activating effect of hydrogen peroxide |
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Authors: | MA Vargas SG Maurio JM Maldonado |
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Institution: | M.A. Vargas, S.G. Mauriño,J.M. Maldonado, |
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Abstract: | Irradiation with white light of spinach leaf nitrate reductase (NR) in the presence of flavin mononucleotide (FMN) and ethylenediaminetetraacetic acid (EDTA) resulted in a gradual loss of the enzyme activity, measured with reduced methyl viologen as electron donor. Inactivation of NR was dependent on oxygen and was prevented by superoxide dismutase. On the contrary, the presence of catalase markedly enhanced the rate of inactivation. Nitrate showed a protective effect. NR previously inactivated by irradiation in the presence of FMN and EDTA was greatly reactivated by a short preincubation of the inactive enzyme with either ferricyanide or H2O2. These results suggest that spinach leaf NR is reversibly inactivated by photogenerated O2
, while H2O2 has an activating effect. |
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Keywords: | Flavin photoreactions hydrogen peroxide nitrate reductase redox regulation Spinacia oleracea superoxide radical |
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