TAILIEUCHUNG - Báo cáo khoa học: Purification of a plant nucleotide pyrophosphatase as a protein that interferes with nitrate reductase and glutamine synthetase assays

An activity that inhibited both glutamine synthetase (GS) and nitrate reductase (NR) was highly purified from cauli-flower (Brassica ) final preparationcontainedanacyl-CoAoxidase andasecond proteinof theplant nucleotidepyrophosphatase preparationhydrolysedNADH, ATPandFAD togenerate AMP andwas inhibited by fluoride, Cu 2+ ,Zn 2+ andNi 2+ . | Eur. J. Biochem. 270 1356-1362 2003 FEBS 2003 doi Purification of a plant nucleotide pyrophosphatase as a protein that interferes with nitrate reductase and glutamine synthetase assays Greg B. G. Moorhead Sarah E. M. Meek Pauline Douglas Dave Bridges Catherine S. Smith Nick Morrice and Carol MacKintosh MRC Protein Phosphorylation Unit Department of Biochemistry University of Dundee UK An activity that inhibited both glutamine synthetase GS and nitrate reductase NR was highly purified from cauliflower Brassica oleracea var. botrytis extracts. The Until preparation contained an acyl-CoA oxidase and a second protein of the plant nucleotide pyrophosphatase family. Th is preparation hydrolysed NADH ATP and FAD to generate AMP and was inhibited by fluoride Cu2 Zn2 and Ni2 . The purified fraction had no effect on the activity of NR when reduced methylviologen was used as electron donor instead of NADH and inhibited the oxidation of NADH by both spinach NR and an Escherichia coli extract in a timedependent apparent inhibition of GS and NR and the ability of ATP and AMP to relieve the inhibition of NR can therefore be explained by hydrolysis of nucleotide substrates by the nucleotide pyrophosphatase. We have no evidence that the nucleotide pyrophosphatase is a specific physiological regulator of NR and GS but suggest that nucleotide pyrophosphatase activity may underlie some confusion in the literature about the effects of nucleotides and protein factors on NR and GS in vitro. Keywords nucleotide pyrophosphatase nucleotide pyrophosphohydrolase nitrate reductase glutamine synthetase AMP nudix hydrolase. In response to water stress or when photosynthesis is blocked the cytosolic enzyme nitrate reductase NR is inhibited by a two-step mechanism firstly a serine residue Ser543 in the spinach enzyme is phosphorylated 1 2 . The phosphorylation alone has no effect on enzyme activity. The addition of a phosphate to this serine within this

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