Ca2+-binding proteins in crayfish abdominal muscle. Evidence for a calmodulin lacking trimethyllysine.

A partially combined procedure for the isolation of some Ca2+-binding proteins from crayfish abdominal muscle is described, and some biochemical and biophysical data are reported. Crayfish calmodulin is similar to other calmodulins isolated from animal tissues, with the exception that it does not contain trimethyllysine. Besides calmodulin, an unknown protein is described which also binds to phenyl-Sepharose in a Ca2+-dependent manner. Despite its similarities with respect to subunit molecular weight and isoelectric point with 'sarcoplasmic calcium-binding proteins', its amino acid composition shows no similarities either with these proteins or with calmodulin. Furthermore, it is shown that sarcoplasmic Ca2+-binding proteins do not bind to phenyl-Sepharose under the same conditions.