Evidence for a Phosphorylated Form of Calmodulin in Chicken Brain and Muscle
Phosphocalmodulin (PCaM) was identified after analysis of calmodulin (CaM) preparations by two-dimensional gel electrophoresis by using a modified ampholyte system to resolve very acidic proteins. The analysis of CaM prepared by the conventional procedure based upon its heat resistance and acidity as well as the analysis of whole urea extracts from brain showed that PCaM was a major component in this tissue. PCaM was 1 pH unit more acidic than CaM, and its electrophoretic mobility, unlike CaM, was not changed by either calcium or ethylene glycol-bis(β-aminoethyl ether)-N,N-tetraacetic acid. In urea extracts of brain prepared in buffers containing phosphate and sodium fluoride, PCaM was as prominent as CaM; it was partially converted into CaM after elution from the gel and reelectrophoresis. Amino acid analysis of PCaM and CaM purified by two-dimensional gel electrophoresis showed the same composition for the two proteins, including their trimethyllysine content. Incorporation of (^32)P occurred exclusively into the acidic variant when brain slices were incubated with (H_3)(^32(PO_4)); amino acid analysis showed that the phosphate was bound to serine residues. CaM was found also to be phosphorylated in vitro by a phosphorylase kinase preparation from skeletal muscle.
Additional Information© 1983 American Society for Microbiology. Received 14 February 1983; Accepted 31 May 1983. We thank B. L. Granger for his comments on the manuscript. This work was supported by grants from the National Institutes of Health, the National Science Foundation, and the Muscular Dystrophy Association of America, Y.D.P. is Charge de Recherches at the C.N.R.S., Paris, France. E.L. is a recipient of a Research Career Development Award from the National Institutes of Health.
Published - PLAmcb83.pdf