Octopus calmodulin. The trimethyllysyl residue is not required for myosin light chain kinase activation.

Octopus calmodulin was purified to homogeneity and shown to contain 0.1 residue each of epsilon-N-monomethyl-lysine, epsilon-N-dimethyllysine, and epsilon-N-trimethyllysine/mol. With the exception of this partial methylation and of a single tyrosyl residue, it shared all the characteristic properties of mammalian calmodulin in terms of molecular weight, amino acid composition, electrophoretic behavior in the presence or absence of Ca2+ ions, and activation of calcium/calmodulin-dependent myosin light chain kinase. In fact, Octopus calmodulin proved to be slightly more effective than ram testis calmodulin in activating both skeletal and smooth muscle myosin light chain kinases in the presence of Ca2+. This provides conclusive evidence that (a) stoichiometric trimethylation of lysine 115 is not required for enzyme activation, and (b) the inability of troponin C to activate myosin light chain kinase (Walsh, M. P., Vallet, B., Cavadore, J. C., and Demaille, J. G.