Phosphorylation by casein kinase II alters the biological activity of calmodulin

D. B. Sacks, H. W. Davis, J. P. Williams, E. L. Sheehan, J. G.N. Garcia, J. M. McDonald

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


Calmodulin is the major intracellular Ca2+-binding protein, providing Ca2+-dependent regulation of numerous intracellular enzymes. The phosphorylation of calmodulin may provide an additional mechanism for modulating its function as a signal transducer. Phosphocalmodulin has been identified in tissues and cells, and calmodulin is phosphorylated both in vitro and in intact cells by various enzymes. Phosphorylation of calmodulin on serine/threonine residues by casein kinase II decreases its ability to activate both myosin-light-chain kinase and cyclic nucleotide phosphodiesterase. For myosin-light-chain kinase the primary effect is an inhibition of the V(max.) of the reaction, with no apparent change in the concentration at which half-maximal velocity is attained (K0.5) for either Ca2+ or calmodulin. In contrast, for phosphodiesterase, phosphorylation of calmodulin significantly increases the K0.5 for calmodulin without noticeably altering the V(max.) or the K0.5 for Ca2+. The higher the stoichiometry of phosphorylation of calmodulin, the greater the inhibition of calmodulin-stimulated activity for both enzymes. Therefore the phosphorylation of calmodulin by casein kinase II appears to provide a Ca2+-independent mechanism whereby calmodulin regulates at least two important target enzymes, myosin-light-chain kinase and cyclic nucleotide phosphodiesterase.

Original languageEnglish (US)
Pages (from-to)21-24
Number of pages4
JournalBiochemical Journal
Issue number1
StatePublished - 1992

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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