Glycogenin - wikipedia Glycogenin glycogenin glucosyltransferase Glycogenin structure ( from rabbit ). Identifiers EC number 2.4. 1.186 CAS number 117590 - 73 - 5 Databases IntEnz IntEnz view BRENDA BRENDA entry ExPASy NiceZyme view KEGG KEGG entry MetaCyc metabolic pathway PRIAM profile PDB structures RCSB PDB PDBe PDBsum Search PMC articles PubMed articles NCBI proteins Glycogenin is an enzyme involved in converting glucose to glycogen. It acts as a primer, by polymerizing the first few glucose molecules, after which other enzymes take over. It is a homodimer of 37 - kDa subunits and is classified as a glycosyltransferase. It catalyzes the chemical reaction : UDP - alpha - D - glucose + glycogenin ⇌ ( displaystyle \rightleftharpoons ) UDP + alpha - D - glucosylglycogenin Thus, the two substrates of this enzyme are UDP - alpha - D - glucose and glycogenin, whereas its two products are UDP and alpha - D - glucosylglycogenin. Contents 1 Nomenclature 2 Discovery 3 Function 4 Structure 5 Isozymes 6 References 7 Further reading 8 External links Nomenclature This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is UDP - alpha - D - glucose : glycogenin alpha - D - glucosyltransferase. Other names in common use include : glycogenin, priming glucosyltransferase, and UDP - glucose : glycogenin glucosyltransferase. Discovery Glycogenin was discovered in 1984 by Dr. William J. Whelan, a fellow of the Royal Society of London and current professor of Biochemistry at the University of Miami. Function The main enzyme involved in glycogen polymerisation, glycogen synthase, can only add to an existing chain of at least 4 glucose residues. Glycogenin acts as the primer, to which further glucose monomers may be added. It achieves this by catalyzing the addition of glucose to itself ( autocatalysis ) by first binding glucose from UDP - glucose to the hydroxyl group of Tyr - 194. Seven more glucoses can be added, each derived from UDP - glucose, by glycogenin 's glucosyltransferase activity. Once sufficient residues have been added, glycogen synthase takes over extending the chain. Glycogenin remains covalently attached to the reducing end of the glycogen molecule. Evidence accumulates that a priming protein may be a fundamental property of polysaccharide synthesis in general ; the molecular details of mammalian glycogen biogenesis may serve as a useful model for other systems. Structure 2 - D cross-sectional view of glycogen. A core protein of glycogenin is surrounded by branches of glucose units. The entire globular complex may contain approximately 30 000 glucose units. Isozymes In humans, there are two isoforms of glycogenin -- glycogenin - 1, encoded by GYG1, and expressed in muscle ; and glycogenin - 2, encoded by GYG2, and expressed in the liver and cardiac muscle, but not skeletal muscle. Patients have been found with defective GYG1, resulting in muscle cells with the inability to store glycogen, and consequential weakness and heart disease. glycogenin 1 Identifiers Symbol GYG1 Alt. symbols GYG Entrez 2992 HUGO 4699 OMIM 603942 RefSeq NM_004130 UniProt P46976 Other data EC number 2.4. 1.186 Locus Chr. 3 q24 - q25. 1 glycogenin 2 Identifiers Symbol GYG2 Entrez 8908 HUGO 4700 OMIM 300198 RefSeq NM_003918 UniProt O15488 Other data EC number 2.4. 1.186 Locus Chr. X p22. 3 References Jump up ^ PDB : 1LL3 ​ ; Gibbons BJ, Roach PJ, Hurley TD ( May 2002 ). `` Crystal structure of the autocatalytic initiator of glycogen biosynthesis, glycogenin ''. J. Mol. Biol. 319 ( 2 ) : 463 -- 77. PMID 12051921. doi : 10.1016 / S0022 - 2836 ( 02 ) 00305 - 4. Jump up ^ Whelan WJ ( September 1998 ). `` Pride and prejudice : the discovery of the primer for glycogen synthesis ''. Protein Sci. 7 ( 9 ) : 2038 -- 41. PMC 2144155. PMID 9761486. doi : 10.1002 / pro. 5560070921. Jump up ^ Katch, Victor L. ; McArdle, William D. ; Katch, Frank I. ( 2007 ). Exercise physiology : energy, nutrition, and human performance. Philadelphia : Lippincott Williams and Wilkins. p. 12. ISBN 0 - 7817 - 4990 - 5. Jump up ^ Moslemi AR, Lindberg C, Nilsson J, Tajsharghi H, Andersson B, Oldfors A ( April 2010 ). `` Glycogenin - 1 deficiency and inactivated priming of glycogen synthesis ''. N. Engl. J. Med. 362 ( 13 ) : 1203 -- 10. PMID 20357282. doi : 10.1056 / NEJMoa0900661. Further reading Krisman CR, Barengo R ( 1975 ). `` A precursor of glycogen biosynthesis : alpha - 1, 4 - glucan - protein ''. Eur. J. Biochem. 52 ( 1 ) : 117 -- 23. PMID 809265. doi : 10.1111 / j. 1432 - 1033.1975. tb03979. x. Pitcher J, Smythe C, Campbell DG, Cohen P ( 1987 ). `` Identification of the 38 - kDa subunit of rabbit skeletal muscle glycogen synthase as glycogenin ''. Eur. J. Biochem. 169 ( 3 ) : 497 -- 502. PMID 3121316. doi : 10.1111 / j. 1432 - 1033.1987. tb13637. x. Pitcher J, Smythe C, Cohen P ( 1988 ). `` Glycogenin is the priming glucosyltransferase required for the initiation of glycogen biogenesis in rabbit skeletal muscle ''. Eur. J. Biochem. 176 ( 2 ) : 391 -- 5. PMID 2970965. doi : 10.1111 / j. 1432 - 1033.1988. tb14294. x. Berman, M.C. and Opie, L.A. ( Eds. ), Membranes and Muscle, ICSU Press / IRL Press, Oxford, 1985, p. 65 - 84. Rodriguez IR, Whelan WJ ( 1985 ). `` A novel glycosyl - amino acid linkage : rabbit - muscle glycogen is covalently linked to a protein via tyrosine ''. Biochem. Biophys. Res. Commun. 132 ( 2 ) : 829 -- 36. PMID 4062948. doi : 10.1016 / 0006 - 291X ( 85 ) 91206 - 9. Lomako J, Lomako WM, Whelan WJ ( 1988 ). `` A self - glucosylating protein is the primer for rabbit muscle glycogen biosynthesis ''. FASEB J. 2 ( 15 ) : 3097 -- 103. PMID 2973423. Alonso MD, Lomako J, Lomako WM, Whelan WJ ( 1995 ). `` Catalytic activities of glycogenin additional to autocatalytic self - glucosylation ''. J. Biol. Chem. 270 ( 25 ) : 15315 -- 9. PMID 7797519. doi : 10.1074 / jbc. 270.25. 15315. Alonso MD, Lomako J, Lomako WM, Whelan WJ ( 1995 ). `` A new look at the biogenesis of glycogen ''. FASEB J. 9 ( 12 ) : 1126 -- 37. PMID 7672505. Mu J, Roach PJ ( 1998 ). `` Characterization of human glycogenin - 2, a self - glucosylating initiator of liver glycogen metabolism ''. J. Biol. Chem. 273 ( 52 ) : 34850 -- 6. PMID 9857012. doi : 10.1074 / jbc. 273.52. 34850. External links glycogenin at the US National Library of Medicine Medical Subject Headings ( MeSH ) http://molbio.med.miami.edu/NewWebsite/Whelan.htm Transferases : glycosyltransferases ( EC 2.4 ) 2.4. 1 : Hexosyl - transferases Glucosyl - Phosphorylase Starch Glycogen Myo - Glycogen synthase Debranching enzyme Branching enzyme 1, 3 - Beta - glucan synthase Ceramide glucosyltransferase Galactosyl - Lactose synthase B-N - acetylglucosaminyl - glycopeptide b - 1, 4 - galactosyltransferase Glycoprotein - N - acetylgalactosamine 3 - beta - galactosyltransferase ( C1GALT1 ) Glucuronosyl - B3GAT1 B3GAT2 B3GAT3 UGT1A1 UGT1A3 UGT1A4 UGT1A5 UGT1A6 UGT1A7 UGT1A8 UGT1A9 UGT1A10 UGT2A1 UGT2A2 UGT2A3 UGT2B4 UGT2B7 UGT2B10 UGT2B11 UGT2B15 UGT2B17 UGT2B28 Hyaluronan synthase : HAS1 HAS2 HAS3 Fucosyl - POFUT1 POFUT2 FUT1 FUT2 FUT3 FUT4 FUT5 FUT6 FUT7 FUT8 FUT9 FUT10 FUT11 Mannosyl - Dolichyl - phosphate - mannose - protein mannosyltransferase POMT1 POMT2 DPM1 DPM3 ALG1 ALG2 ALG3 ALG6 ALG8 ALG9 ALG12 2.4. 2 : Pentosyl - transferases Ribose ADP - ribosyltransferase NAD : diphthamide ADP - ribosyltransferase Diphtheria toxin NAD ( P ) : arginine ADP - ribosyltransferase Pertussis toxin Cholera toxin Poly ADP ribose polymerase Sirtuin Phosphoribosyltransferase Adenine phosphoribosyltransferase Hypoxanthine - guanine phosphoribosyltransferase Uracil phosphoribosyltransferase Amidophosphoribosyltransferase Other Purine nucleoside phosphorylase : Thymidine phosphorylase ECGF1 Other Xylosyltransferase XYLT1 XYLT2 Arabinosyltransferase Indolylacetylinositol arabinosyltransferase 2.4. 99 : Sialyl transferases Beta - galactoside alpha - 2, 6 - sialyltransferase Monosialoganglioside sialyltransferase ST8SIA4 Enzymes Activity Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Catalytically perfect enzyme Coenzyme Cofactor Enzyme catalysis Regulation Allosteric regulation Cooperativity Enzyme inhibitor Classification EC number Enzyme superfamily Enzyme family List of enzymes Kinetics Enzyme kinetics Eadie -- Hofstee diagram Hanes -- Woolf plot Lineweaver -- Burk plot Michaelis -- Menten kinetics Types EC1 Oxidoreductases ( list ) EC2 Transferases ( list ) EC3 Hydrolases ( list ) EC4 Lyases ( list ) EC5 Isomerases ( list ) EC6 Ligases ( list ) Molecular and Cellular Biology portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Glycogenin&oldid=783715278 '' Categories : Genes on human chromosome 3 Genes on human chromosome X EC 2.4. 1 Enzymes of known structure Hidden categories : Protein pages needing a picture Talk Search Contents About Wikipedia Deutsch Español Français Hrvatski Italiano Српски / srpski Srpskohrvatski / српскохрватски Suomi Edit links This page was last edited on 4 June 2017, at 04 : 33. 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Question: explain the role of glycogenin in glycogen synthesis
Answer: acts as a primer, by polymerizing the first few glucose molecules