title: The substrate specificity of isoamylase and the preparation of apo-glycogenin.
abstract: A new facet of the specificity of the glycogen-debranching enzyme, isoamylase, namely, the hydrolysis of a carbohydrate-amino acid linkage, is described. This bond joins the terminal, reducing-end D-glucose unit of glycogen to the hydroxyl group of tyrosine in glycogenin, the primer protein for glycogen biogenesis. The specificity was further defined by demonstrating that 4-nitrophenyl alpha-maltotrioside and higher homologs also act as substrates. The splitting of the glycogen-glycogenin bond by isoamylase indicates the alpha-anomeric configuration of the terminal D-glucose unit. It also provides a means of preparing apo-glycogenin. Pullulanase, a somewhat similar starch- and glycogen-debranching enzyme, does not split these new isoamylase substrates, permitting the 4-nitrophenyl saccharides to be used in distinguishing between isoamylase and pullulanase.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Florida 33101.
authors.forename: J
authors.initials: J
authors.lastname: Lomako
authors.forename: W M
authors.initials: WM
authors.lastname: Lomako
authors.forename: W J
authors.initials: WJ
authors.lastname: Whelan
mesh_terms: D005964:Glucosyltransferases; D006003:Glycogen / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000378:metabolism*; D007517:Isoamylase / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D006023:Glycoproteins; C051887:glycogenin; D006003:Glycogen; D005964:Glucosyltransferases; D006026:Glycoside Hydrolases; C100181:pullulanase; D007517:Isoamylase