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Biochim Biophys Acta. 1992 Aug 12;1136(2):203-7.

Cell-free phosphorylation of the murine small heat-shock protein hsp25 by an endogenous kinase from Ehrlich ascites tumor cells.

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1
Max-Delbrück-Centrum für Molekulare Medizin, Berlin-Buch, Germany.

Abstract

The small heat-shock protein hsp25 of the Ehrlich ascites tumor exists in one non-phosphorylated (hsp25/1) and two phosphorylated (hsp25/2, hsp25/3) isoforms. In stationary phase tumor cells, a protein kinase activity was detected which phosphorylates hsp25/1, resulting in the formation of several phosphorylated hsp25 isoforms, including those occurring naturally in the tumor. Cell-free phosphorylation of hsp25 required Mg2+ and ATP and was independent of Ca2+, phosphatidylserine, cAMP and cGMP. Polymyxin B inhibited, specifically, hsp25 phosphorylation, whereas trifluoperazine, staurosporine and the protein inhibitor of protein kinase A had no effect. In its properties, the hsp25 phosphorylating kinase differs from other common kinases such as protein kinases A and C, calcium/calmodulin-dependent kinases, and the ribosomal protein S6 kinase.

PMID:
1504105
[Indexed for MEDLINE]

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