Homology of the .gamma. subunit of phosphorylase b kinase with cAMP-dependent protein kinase

Abstract

The complete amino acid sequence of the catalytic subunit (.gamma. subunit) of rabbit skeletal muscle phosphorylase b kinase was determined. The .gamma. subunit was purified by gel filtration in acidic 8 M urea after reduction and S-carboxymethylation in 7 M guanidine hydrochloride. Cleavage of the .gamma. subunit at arginyl bonds gave a complete set of nonoverlapping peptides. Overlapping peptides were obtained by cleavage at methionyl, tryptophanyl or glutamyl bonds and by selected subdigestion of 2 large peptides obtained by cleavage at methionyl bonds. Sequence analysis established that the protein contains 386 residues corresponding to a MW of 44,673. Comparison of the .gamma. subunit with the catalytic subunit of bovine cAMP-dependent protein kinase and with tyrosine-specific kinases of viral origin revealed a significant degree of sequence identity among all of these proteins. Ca-dependent protein kinases may share a common ancestral gene and a common structural basis for catalytic function with a wide variety of other protein kinases which respond to different signals and control quite diferent processes.