Cytosolic glutamine synthetase and not nitrate reductase from the green alga Chlamydomonas reinhardtii is phosphorylated and binds 14-3-3 proteins |
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Authors: | Mercedes Pozuelo Carol MacKintosh Aurora Galván Emilio Fernández |
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Affiliation: | (1) Departamento de Bioquímica y Biología Molecular, Campus de Rabanales, Edif. C-6. Universidad de Córdoba, 14071 Córdoba, Spain, ES;(2) MRC Protein Phosphorylation Unit, Biochemistry Department, University of Dundee, DD1 4HN, UK, GB |
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Abstract: | The nitrate reductase activity from Chlamydomonas reinhardtii was not altered when extracts were incubated with yeast 14-3-3 proteins in the presence of Mg-ATP. However, the C. reinhardtii extracts contained 14-3-3 proteins capable of inhibiting the spinach nitrate reductase, raising the question of their physiological substrates. Two C. reinhardtii proteins of about 48 and 35 kDa were eluted from 14-3-3 affinity chromatography columns and bound to 14-3-3s in overlay assays. The 48-kDa protein corresponded to the cytosolic isoform of glutamine synthetase (GS1). The GS1 was phosphorylated by a Ca2+- and calmodulin-dependent protein kinase partially purified from the alga. However, neither phosphorylation nor 14-3-3 binding seemed to change GS catalytic activity. Received: 3 February 2000 / Accepted: 6 May 2000 |
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Keywords: | : Chlamydomonas Glutamine synthetase Nitrate reductase Nitrate assimilation 14-3-3 Protein |
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