Isolation, distribution, and characterization of peach seedling nitrate reductase1

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Abstract
Nitrate reductase (NR) was extracted from leaf, root, and stem tissue of ‘Lovell’ peach seedlings [Prunus persica (L.) Batsch] grown for 8 weeks in nutrient solution containing 15 mM nitrate. Enzyme activity of NR in leaf, stem, and root tissue was 10.20: 0.07: 0.04 nM N02/min/g tissue extracted, respectively. When seedlings wee transferred to nutrient solution containing 15 mM NH4, NR activity was not detected after 72 hours. The enzyme was specific for NADH and had a pH optimum of 7.5. The Km for NO3 was 1.3 x 10–3 M and the rate of reaction remained linear for 45 min. Enzyme activity of leaf tissue was dependent on NO3 concentration in the nutrient solution. At NO3 concentrations of 15, 7.5, 1.5, and 0.15 mM, the NR activity was 22.8, 16.2, 13.8, and 2.2 nM NO2/mg protein/hr.