The alpha and beta subunits of phosphorylase kinase are homologous: cDNA cloning and primary structure of the beta subunit.

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Abstract
We have cloned cDNA molecules encoding the .beta. subunit of phosphorylase kinase (ATP:phosphorylase-b phosphotranferse; EC 2.7.1.38) from rabbit fast-twitch skeletal muscle and have determined the complete primary structure of the polypeptide by a combination of peptide and DNA sequencing. In the mature .beta. subunit, the initial methionine is replaced by an acetyl group. The subunit is composed of 1092 amino acids and has a calculated molecular mass of 125,205 Da. Alignment of its sequence with the .alpha. subunit of phosphorylase kinase reveals extensive regions of homology, but each molecule also possesses unique sequences. Two of the three phosphorylation sites known for the .beta. subunit and all seven phosphorylation sites known for the .alpha. subunit are located in these unique domains.