Modifications of the activity of nitrate reductase from cucumber roots
2006
Reda, M.(Wroclaw Univ. (Poland). Plant Physiology Dept.) E-mail:[email protected] | Klobus, G.(Wroclaw Univ. (Poland). Plant Physiology Dept.)
The regulatory properties of NADH-dependent nitrate reductase (NR) in desalted root extracts from hydroponically grown cucumber seedlings were examined. The lowest activity of NR was detected in extracts incubated with Mg2+ and ATP. An inhibitory effect of Mg-ATP was cancelled in the presence of staurosporine and completely reversed after addition of ethylenediaminetetraacetate (EDTA) as well as AMP. Reactivation of enzyme due to AMP presence, contrary to the chelator-dependent NR activation, was sensitive to microcystin LR. The nitrate reductase in cucumber roots was regulated through reversible phosphorylation of enzyme protein. A drop in the activity of NR was also observed at low pH. At low pH, the presence of ATP alone in the incubation medium was sufficient to inactivate NR. ATP-dependent inactivation of NR at low pH was prevented by staurosporine and reversed by AMP. However, AMP action was not altered by microcystin LR.
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