Romero JM, Curtino JA. C-chain-bound glycogenin is released from proteoglycogen by isoamylase and is able to autoglucosylate.
Biochem Biophys Res Commun 2003;
305:811-4. [PMID:
12767902 DOI:
10.1016/s0006-291x(03)00861-1]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
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.
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