C-chain-bound glycogenin is released from proteoglycogen by isoamylase and is able to autoglucosylate.
Proteoglycogen glycogenin is linked to the glucose residue of the C-chain reducing end of glycogen. We describe for the first time the release by isoamylase and isolation of C-chain-bound glycogenin (C-glycogenin) from proteoglycogen. The treatment of proteoglycogen with alpha-amylase releases monoglucosylated and diglucosylated glycogenin (a-glycogenin) which is able to autoglucosylate. It had been described that isoamylase splits the glucose-glycogenin linkage of fully autoglucosylated glycogenin previously digested with trypsin, releasing the maltosaccharide moiety. It was also described that carbohydrate-free apo-glycogenin shows higher mobility in SDS-PAGE and twice the autoglucosylation capacity of partly glucosylated glycogenin. On the contrary, we found that the C-glycogenin released from proteoglycogen by isoamylolysis shows lower mobility in SDS-PAGE and about half the autoglucosylation acceptor capacity of the partly glucosylated a-glycogenin. This behavior is consistent with the release of maltosaccharide-bound glycogenin instead of apo-glycogenin. No label was split from auto-[14C]glucosylated C-glycogenin or fully auto-[14C]glucosylated a-glycogenin subjected to isoamylolysis without previous trypsinolysis, thus proving no hydrolysis of the maltosaccharide-tyrosine linkage. The ability of C-glycogenin for autoglucosylation would indicate that the size of the C-chain is lower than the average length of the other glycogen chains.
Romero
Jorge M
JM
Centro de Investigaciones en Química Biológica de Córdoba, UNC-CONICET, Departamento de Química Biológica Dr. Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 500 Córdoba, Argentina.
Curtino
Juan A
JA
D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D005947:Glucose / Q000378:metabolism; D005964:Glucosyltransferases; D006003:Glycogen / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006031:Glycosylation; D007517:Isoamylase / Q000378:metabolism*; D007700:Kinetics; D011817:Rabbits; D000516:alpha-Amylases / Q000378:metabolism
D006023:Glycoproteins; C051887:glycogenin; D006003:Glycogen; D005964:Glucosyltransferases; D000516:alpha-Amylases; D007517:Isoamylase; D005947:Glucose