Cytosolic glutamine synthetase and not nitrate reductase from the green alga Chlamydomonas reinhardtii is phosphorylated and binds 14-3-3 proteins

Mercedes Pozuelo, Carol MacKintosh, Aurora Galvan, Emilio Fernandez

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    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 (GSI). The C;SI was phosphorylated by a Ca2+ and calmodulin-dependent protein kinase partially purified from the alga. How-ever, neither phosphorylation nor 14-3-3 binding seemed to change GS catalytic activity.

    Original languageEnglish
    Pages (from-to)264-269
    Number of pages6
    Issue number2
    Publication statusPublished - Jan 2001

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