Phosphorylation of Calmodulin by the Epidermal‐growth‐factor‐receptor Tyrosine Kinase

Abstract

8 pages, 9 figures.-- Now known as FEBS Journal: Open Access content older than 1 year.An epidermal-growth-factor(EGF)-receptor preparation isolated by calmodulin-affinity chromatography from rat liver plasma membranes is able to phosphorylate calmodulin. Calmodulin phosphorylation was enhanced 3–8-fold by EGF, was dependent on the presence of a polycation or basic protein and was inhibited by micromolar concentrations of Ca2+. Phosphate incorporation into calmodulin occurs predominantly on tyrosine residues. Partial proteolysis of phosphocalmodulin by thrombin identifies Tyr99, located in the third calcium-binding domain of calmodulin, as the phosphorylated residue. Stoichiometric measurements show a 32P/calmodulin molar ratio of approximately 1 when optimal phosphorylation conditions are used.This work was supported in part by Research Grants\ud to A. V. from the Comisión Interministerial de Ciencia y Tecnología (SAF392/93), and from the Secretaria de Educación de la Comunidad\ud de Madrid (366/92). A. B. is the recipient of a predoctoral fellowship from the Departamento de Educación, Universidades e Investigación\ud del Gobierno Vasco, 0. H.-P. is the recipient of a predoctoral fellowships from the Cabildo Insular de Gran Canaria, Fundacion\ud Universitaria de Las Palmas, and from the Funducidn Científica de la Asociación Española Contra el Cancer, and M. T. M.-P.\ud is the recepient of an undergraduate traineeship from the Consejo Superior de Investigaciones Cientipcas. Work at D. B. S. lab was\ud supported by Research Grant DK43682 from the National Institutes of Health. USA.Peer reviewe