A calmodulin-dependent protein kinase has been purified extensively from a Rous sarcoma virus-transformed rat cell line (RR1022) and from normal rat liver. The calmodulin-dependent protein kinase activity was manifested by in vitro phosphorylation of a single Mr 57 000 endogenous phosphoprotein (pp57) present in both the virally transformed cells and normal rat liver. The calmodulin-dependent protein kinase from transformed cells fractionated with the viral src gene product, pp60v-src, through a 650-fold purification of the oncogene product. However, purification of the calmodulin-dependent protein kinase from normal liver demonstrated that the calmodulin-dependent kinase was distinct from pp60v-src. Phosphorylation of pp57 by the kinase purified from the transformed cell line required Ca2+ and calmodulin, was inhibited by EDTA and was unaffected by cAMP or the heat- and acid-stable protein inhibitor of cAMP-dependent protein kinase. Troponin C did not substitute for calmodulin. A virtually identical calmodulin-dependent protein kinase activity was purified from rat liver by affinity chromatography on calmodulin-Sepharose. Phosphorylation of pp57 by the affinity-purified liver protein kinase was also observed, and required Ca2+ and calmodulin. EGTA and trifluoroperazine inhibited pp57 phosphorylation. The calmodulin-dependent protein kinase reported here did not phosphorylate substrates of known calmodulin-dependent protein kinases in vitro (myosin light chain, phosphorylase b, glycogen synthease, microtubule-associated proteins, tubulin, α-casein). Because none of these proteins served as substrates in vitro and pp57 was the only endogenous substrate found, the properties of this enzyme appear to be different from any previously described calmodulin-dependent protein kinase.
|Number of pages||8|
|Journal||Biochimica et Biophysica Acta - Molecular Cell Research|
|State||Published - Feb 21 1985|
Bibliographical noteFunding Information:
This work was supported by grants from the National Science Foundation No. PCM-8203857 and No. PCM-8302912, American Cancer Society No. BC-416 and IN-25V, National Institutes of Health GM30861 and GM30953 and the National Cancer Institute No. 2-PO1-CA19014 and No. 5T32-CA09156.
- (Rat liver)
- Calmodulin dependence
- Protein kinase
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology