The occurrence of serine phosphate in glycogenin: a possible regulatory site.
Glycogenin is the covalently bound protein found in muscle glycogen that is thought to be the primer for glycogen synthesis. We now report that glycogenin contains a phosphoserine residue. From a less than stoichiometric amount of phosphate in glycogenin as isolated, the content may be increased to one molecular proportion, using the catalytic subunit of cAMP-dependent protein kinase. The phosphoserine residue is present within a hitherto-undescribed amino acid sequence. In particular, the serine is not flanked by arginine, previously thought to be an essential adjunct for a serine residue to act as substrate for this kinase. We suggest that the serine phosphate may represent a means of regulating the ability of glycogenin to prime glycogen synthesis.
Lomako
J
J
Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, FL 33101.
Whelan
W J
WJ
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D005964:Glucosyltransferases; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D009132:Muscles / Q000032:analysis; D010710:Phosphates / Q000032:analysis; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D011817:Rabbits; D012694:Serine / Q000031:analogs & derivatives*
D006023:Glycoproteins; D010710:Phosphates; C051887:glycogenin; D010768:Phosphoserine; D012694:Serine; D005964:Glucosyltransferases; D011494:Protein Kinases