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A novel, calcium‐inhibitable casein kinase in Paramecium cells
Author(s) -
Kissmehl Roland,
Treptau Tilman,
Hauser Karin,
Plattner Helmut
Publication year - 1997
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(96)01539-6
Subject(s) - casein kinase 2, alpha 1 , dephosphorylation , autophosphorylation , biochemistry , casein kinase 2 , phosphorylation , casein kinase 1 , kinase , protein kinase a , biology , phosphatase , paramecium , microbiology and biotechnology , casein , chemistry , mitogen activated protein kinase kinase
This is the first identification of a Ca 2+ ‐inhibitable casein kinase (CPK) which we have isolated from the 100 000× g supernatant of Paramecium cell homogenates. The 1000‐fold enriched CPK activity depends on millimolar Mg 2+ and is inhibited by low concentrations of heparin or by ≥100 μM Ca 2+ . Enzyme activity is stimulated by polylysine or polyarginine with either casein or with specific casein kinase‐2 (CK‐2) peptide substrates (RRRDDDSDDD and RREEETEEE). The enzymic properties are similar with GTP instead of ATP. CPK does not undergo autophosphorylation. In gel kinase assays, enzyme activity is associated with a 36 kDa band. Calmodulin as another characteristic substrate for mammalian CK‐2 has not been phosphorylated by this protein kinase. Besides casein, CPK phosphorylates in vitro the catalytic subunit of bovine brain calcineurin (CaN), a typical substrate of type 1 mammalian casein kinase (CK‐1) in vitro. Again this phosphorylation is significantly reduced by Ca 2+ . Thus, CPK combines aspects of different casein kinases, but it is clearly different from any type known by its Ca 2+ inhibition. Since CPK also phosphorylates the exocytosis‐sensitive phosphoprotein, PP63, in Paramecium , which is known to be dephosphorylated by CaN, an antagonistic Ca 2+ ‐effect during phosphorylation/dephosphorylation cycles may be relevant for exocytosis regulation.