{"id":400,"date":"2019-04-15T10:53:21","date_gmt":"2019-04-15T10:53:21","guid":{"rendered":"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/?post_type=chapter&#038;p=400"},"modified":"2019-04-15T10:56:28","modified_gmt":"2019-04-15T10:56:28","slug":"glycogenolysis","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/chapter\/glycogenolysis\/","title":{"rendered":"Glycogenolysis"},"content":{"raw":"<div><span style=\"float: right\"><a href=\"https:\/\/youtu.be\/NLSTHlBahcM\" target=\"_blank\" rel=\"noopener\"><img src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"epgp books\" width=\"75px\" height=\"75px;\" \/><\/a>\r\n<\/span><\/div>\r\n<strong>\u00a0 \u00a0<\/strong>\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n<strong>GLYCOGENOLYSIS<\/strong>\r\n\r\n&nbsp;\r\n\r\n<strong>Objectives<\/strong>\r\n<ol>\r\n \t<li>To understand the breakdown of glycogen.<\/li>\r\n \t<li>To understand the role of glycogen phosphorylase in glycogen breakdown.<\/li>\r\n \t<li>To understand the role of Glycogen Debranching enzyme<\/li>\r\n<\/ol>\r\n<strong>\u00a0 \u00a0<\/strong>\r\n\r\n<strong>Introduction<\/strong>\r\n<ul>\r\n \t<li style=\"text-align: justify\">The biological degradation of glycogen is termed as <strong>glycogenolysis.<\/strong><\/li>\r\n<\/ul>\r\n<ul>\r\n \t<li style=\"text-align: justify\">Glycogen is a highly branched, large polymer of glucose molecules linked along its main line by \u03b1-1, 4 glycosidic linkages; branches arise by \u03b1-1,6 glycosidic bond at about every tenth residues.<\/li>\r\n<\/ul>\r\n<img class=\"aligncenter size-full wp-image-401\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-208.png\" alt=\"\" width=\"627\" height=\"307\" \/>\r\n<p style=\"text-align: center\"><strong>Fig: 25.1 STRUCTURE OF GLYCOGEN<\/strong><\/p>\r\n&nbsp;\r\n<ul>\r\n \t<li style=\"text-align: justify\">Glycogen founds in the cytoplasm as granules. Granules also contain the enzymes and regulatory proteins which is required for its synthesis and degradation.It acts as an important energy reserve for the body. It is stored in the liver and skeletal muscle.Glycogen stored in the muscles will be utilized for the energy requirement of muscles only, while glycogen stored in the liver will be used for the energy requirement of the rest of the body.<\/li>\r\n<\/ul>\r\n<ul>\r\n \t<li style=\"text-align: justify\">Regulation of glycogenesis and glycogenolysis is very important in maintaining the glycogen homeostasis. These two processes are commonly regulated. Hormones which stimulate glycogenolysis (e.g. glucagon,\u00a0 cortisol, epinephrine,\u00a0norepinephrine<span style=\"text-align: initial;font-size: 1em\">) concurrently inhibit glycogenesis. On the other hand, insulin, which promotes the body to store glycogenesis, is inhibiting glycogenolysis.<\/span>\r\n<ul>\r\n \t<li>Glycogen is degraded by two different pathways. In the first, glucose is released in muscles to fuel its contraction or it is released in liver to transport it in to the blood. It is catalysed by the Glycogen phosphorylase and Debranching enzyme. In the second pathway, glycogen is degraded to glucose within the lysosome by the enzyme \u03b1-glucosidase and acid maltase.<\/li>\r\n<\/ul>\r\n&nbsp;\r\n<ul>\r\n \t<li>Glycogen metabolism is very important because it facilitate the blood glucose level to be maintained between meals (liver glycogen) and also act as an energy reserve for muscular activity. The maintenanceof blood glucose is essential in order to supply energy to tissues.<\/li>\r\n<\/ul>\r\n<img class=\"aligncenter size-full wp-image-402\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-209.png\" alt=\"\" width=\"422\" height=\"249\" \/><\/li>\r\n<\/ul>\r\n<strong>\u00a0 \u00a0 STEPS OF GLYCOGENOLYSIS<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">Glycogenolysis requires2main enzymes. Glycogenolysisoccurs by a different pathway from glycogenesis.<\/p>\r\n\r\n<ol style=\"text-align: justify\">\r\n \t<li>Glucose-1-phosphate formation from non reducing end of glycogen by Glycogen phosphorylase<\/li>\r\n<\/ol>\r\n<ol style=\"text-align: justify\" start=\"2\">\r\n \t<li>Removal of \u03b1-1,6 branches from glycogen by Glycogen Debranching enzyme<\/li>\r\n<\/ol>\r\n<ol start=\"3\">\r\n \t<li style=\"text-align: justify\">Glucose-6-phosphate formation from Glucose-1-phosphateby Phosphoglucomutase.<\/li>\r\n<\/ol>\r\n<img class=\"aligncenter size-full wp-image-403\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-210.png\" alt=\"\" width=\"531\" height=\"413\" \/>\r\n<p style=\"text-align: center\"><strong>Fig: 24.2OVERVIEW OF GLYCOGENOLYSIS<\/strong><\/p>\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n<strong>1. Glucose-1-phosphate formation from non reducing end of glycogen by Glycogen phosphorylase<\/strong>\r\n<ul>\r\n \t<li>Glycogen is\u00a0 broken-down\u00a0 in\u00a0 to\u00a0 Glucose-1-Phosphate\u00a0 (G1P)\u00a0 by\u00a0 Glycogen<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">\u00a0 \u00a0 \u00a0 \u00a0 Phosphorylase. It is carried out by\u00a0phosphorolysis reaction. Phosphorolysis\u00a0 reaction involves the cleavage of larger molecules into smaller molecules. It uses phosphate for the cleavage. Such breakdown of bonds by the addition of orthophosphate is referred to as phosphorolysis. A hydrolysis reaction also involves the same process but it uses water instead of phosphate for the cleavage of bond.<\/p>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter size-full wp-image-404\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-211.png\" alt=\"\" width=\"471\" height=\"449\" \/>\r\n<p style=\"text-align: center\"><strong>Fig: 24.3 Formation of G- 1-P from glycogen<\/strong><\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\">Cleavage by phosphorolysis is energetically favourable because released glucose is phosphorylated. While hydrolytically release of sugar needs to be phosphorylated before enters into the glycolytic pathway.<\/li>\r\n<\/ul>\r\n<ul>\r\n \t<li style=\"text-align: justify\">Glycogen phosphorylase act on exoglycosidic bond. Pyridoxal phosphate is an necessary cofactor in the glycogen phosphorylase reaction. This cofactor is linked to lysine 680 of the enzyme.<\/li>\r\n<\/ul>\r\n<ul style=\"text-align: justify\">\r\n \t<li>Glycogen phosphorylase will act repeatedly on non-reducing ends of a glycogen chain. Glycogen phosphorylase can act continuously until it reaches 4 glucose away from \u03b1 1-6 branch point.<\/li>\r\n<\/ul>\r\n<ul style=\"text-align: justify\">\r\n \t<li>Glycogen phosphorylase is an allosteric enzyme. AMP acts as an allosteric activator while ATP, G6P and glucose acts as an allosteric inhibitor. Glycogen phosphorylase is also regulated by covalent modification. ( For further details please refer module:26 ,<span style=\"text-align: initial;font-size: 1em\"> regulation of glycogen degradation)<\/span><\/li>\r\n<\/ul>\r\n<ul>\r\n \t<li style=\"text-align: justify\">Generally in the structure of glycogen about 1 in 10 residues is branched. In such situation phosphorylase enzyme cannot degrade glycogen independently. It will stop to a halt after the release of six glucose molecules per branch.<\/li>\r\n<\/ul>\r\n&nbsp;\r\n\r\n<strong>2. Removal of \u03b1-1,6 branches from glycogen by Glycogen Debranching enzyme<\/strong>\r\n<ul>\r\n \t<li style=\"text-align: justify\">In glycogen, \u03b1- 1-6 glycosidic bonds at the branch point are not susceptible to cleavage by glycogen phosphorylase while it can act continuously until it reaches four glucose away from \u03b1 1-6 branch point. Thus further degradation of glycogen chain by glycogen phosphorylase occurs only after the action of a glycogen debranching enzyme.<\/li>\r\n<\/ul>\r\n<ul>\r\n \t<li>Glycogen debranching enzyme shows two different activities.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">\u00a0 \u00a0 o Transferase activity<\/p>\r\n<p style=\"text-align: justify\">o \u03b1 1\u00e06 glucosidase activity<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\">In transferase activity, the enzyme removes and transfers terminal 3 of the 4 glucose residues. It transfers this moiety intact to the non reducing end of another branch. It involves cleaving of an \u03b1 (1\u00e04) linkage and formation of new \u03b1 (1\u00e04) linkage in another branch. This action leaves a single<span style=\"text-align: initial;font-size: 1em\"> glucose at the \u03b11,6 branch.<\/span><\/li>\r\n<\/ul>\r\n<ul style=\"text-align: justify\">\r\n \t<li>In \u03b1 1\u00e06 glucosidase activity, enzyme removes the single glucose residue which is remaining at branch point by an alpha (1\u00e06 glucosidase activity of the same debranching enzyme.<\/li>\r\n<\/ul>\r\n<ul>\r\n \t<li style=\"text-align: justify\">91 % of the glycogen residues are converted to Glucose-1-phosphate by the combined activity of glycogen phosphorylase and glycogen debranching enzyme.<\/li>\r\n<\/ul>\r\n&nbsp;\r\n<p style=\"text-align: justify\">Remaining about 8 % are converted to glucose by the \u03b1 1\u00e06 glucosidase activity of the glycogen debranching enzyme.<\/p>\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n<strong>3. Glucose-6-phosphate formation from Glucose-1-phosphate by Phosphoglucomutase<\/strong>\r\n<ul>\r\n \t<li style=\"text-align: justify\">Glucose-1-phosphate is converted to Glucose-6-phosphate by Phosphoglucomutase.<\/li>\r\n<\/ul>\r\n<ul style=\"text-align: justify\">\r\n \t<li>Active site of the active Phosphoglucomutase molecule has a phosphorylated serine residue. The phosphoryl group istransferred from the amino acid serine to the hydroxyl group (C-6) of glucose 1-phosphate. It result in to<span style=\"text-align: initial;font-size: 1em\"> the formation of intermediate called glucose1, 6-bisphosphate. The phosphoryl group from the C-1\u00a0<\/span>of glucose 1, 6-bisphosphate is then transfer<span style=\"text-align: initial;font-size: 1em\"> to the serine residue of the enzyme. It results <\/span>in to<span style=\"text-align: initial;font-size: 1em\"> the formation of glucose 6-phosphate and the regeneration of the enzyme.<\/span><\/li>\r\n<\/ul>\r\n<div>\r\n<ul>\r\n \t<li style=\"text-align: justify\">\u00a0This reaction is reversible. It allows the inter conversion of Glucose-6-Phosphate and Glucose-1-Phosphate. This isvery important. Phosphoglucomutase is also required to form.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<span style=\"text-align: initial;font-size: 1em\"><span style=\"text-align: initial;font-size: 1em\"><img class=\"aligncenter size-full wp-image-405\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-212.png\" alt=\"\" width=\"653\" height=\"292\" \/><\/span><\/span>\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n<table>\r\n<tbody>\r\n<tr>\r\n<td><strong>you can view video on Glycogenolysis<\/strong><\/td>\r\n<td><a href=\"https:\/\/youtu.be\/NLSTHlBahcM\" target=\"_blank\" rel=\"noopener\"><img class=\"alignnone wp-image-120\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"\" width=\"36\" height=\"36\" \/><\/a><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n&nbsp;\r\n<div class=\"textbox learning-objectives\">\r\n<h3>References<\/h3>\r\n<ul>\r\n \t<li style=\"text-align: justify\">Peter J. Roach, Anna A. Depaoli-Roach, Thomas D. Hurley, Vincent S. Tagliabracci (2012) Glycogen and its metabolism: some new developments and old themes . Biochemical Journal, 441 (3) 763-787; DOI: 10.1042\/BJ20111416<\/li>\r\n \t<li style=\"text-align: justify\">Roach PJ, Depaoli-Roach AA, Hurley TD, Tagliabracci VS (2012) Glycogen and its metabolism: some new developments and old themes. Biochem J 441: 763\u2013787. doi: 10.1042\/BJ20111416<\/li>\r\n \t<li style=\"text-align: justify\">Wilson WA, Roach PJ, Montero M, Baroja-Fernandez E, Munoz FJ, Eydallin G, et al. Regulation of glycogen metabolism in yeast and bacteria. Fems Microbiol Rev. 2010;34(6):952\u2013985.<\/li>\r\n<\/ul>\r\n&nbsp;\r\n\r\n<strong>Web site<\/strong>\r\n<ul>\r\n \t<li>http:\/\/www.wiley.com\/college\/fob\/quiz\/quiz15\/15-20.swf<\/li>\r\n \t<li>https:\/\/www.tamu.edu\/faculty\/bmiles\/lectures\/Glycogen%20Metabolism.pdf<\/li>\r\n \t<li>http:\/\/themedicalbiochemistrypage.org\/glycogen.php<\/li>\r\n \t<li>https:\/\/en.wikibooks.org\/wiki\/Principles_of_Biochemistry<\/li>\r\n<\/ul>\r\n&nbsp;\r\n\r\n<strong>Books<\/strong>\r\n<ul>\r\n \t<li style=\"text-align: justify\">Harper\u2019sIllustrated Biochemistry by Robert K.. Murray, Daryl K. Granner, Peter A. Mayes, 26th Edition (2003)<\/li>\r\n \t<li style=\"text-align: justify\">Lehninger\u2019S Principle of Biochemistry David L. Nelson and Michael M. Cox,5th Edition (2008)<\/li>\r\n \t<li style=\"text-align: justify\">Instant Notes: Biochemistry, 2nd Edition, B.D. Hames &amp; N. M. Hooper (2005)<\/li>\r\n \t<li style=\"text-align: justify\">Textbook of Biochemistry, 4th Edition Donald Voet, Judith G. Voet(2011)<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\"><\/p>\r\n\r\n<\/div>\r\n&nbsp;","rendered":"<div><span style=\"float: right\"><a href=\"https:\/\/youtu.be\/NLSTHlBahcM\" target=\"_blank\" rel=\"noopener\"><img decoding=\"async\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"epgp books\" width=\"75px\" height=\"75px;\" \/><\/a><br \/>\n<\/span><\/div>\n<p><strong>\u00a0 \u00a0<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><strong>GLYCOGENOLYSIS<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Objectives<\/strong><\/p>\n<ol>\n<li>To understand the breakdown of glycogen.<\/li>\n<li>To understand the role of glycogen phosphorylase in glycogen breakdown.<\/li>\n<li>To understand the role of Glycogen Debranching enzyme<\/li>\n<\/ol>\n<p><strong>\u00a0 \u00a0<\/strong><\/p>\n<p><strong>Introduction<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify\">The biological degradation of glycogen is termed as <strong>glycogenolysis.<\/strong><\/li>\n<\/ul>\n<ul>\n<li style=\"text-align: justify\">Glycogen is a highly branched, large polymer of glucose molecules linked along its main line by \u03b1-1, 4 glycosidic linkages; branches arise by \u03b1-1,6 glycosidic bond at about every tenth residues.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-401\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-208.png\" alt=\"\" width=\"627\" height=\"307\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-208.png 627w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-208-300x147.png 300w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-208-65x32.png 65w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-208-225x110.png 225w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-208-350x171.png 350w\" sizes=\"auto, (max-width: 627px) 100vw, 627px\" \/><\/p>\n<p style=\"text-align: center\"><strong>Fig: 25.1 STRUCTURE OF GLYCOGEN<\/strong><\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li style=\"text-align: justify\">Glycogen founds in the cytoplasm as granules. Granules also contain the enzymes and regulatory proteins which is required for its synthesis and degradation.It acts as an important energy reserve for the body. It is stored in the liver and skeletal muscle.Glycogen stored in the muscles will be utilized for the energy requirement of muscles only, while glycogen stored in the liver will be used for the energy requirement of the rest of the body.<\/li>\n<\/ul>\n<ul>\n<li style=\"text-align: justify\">Regulation of glycogenesis and glycogenolysis is very important in maintaining the glycogen homeostasis. These two processes are commonly regulated. Hormones which stimulate glycogenolysis (e.g. glucagon,\u00a0 cortisol, epinephrine,\u00a0norepinephrine<span style=\"text-align: initial;font-size: 1em\">) concurrently inhibit glycogenesis. On the other hand, insulin, which promotes the body to store glycogenesis, is inhibiting glycogenolysis.<\/span>\n<ul>\n<li>Glycogen is degraded by two different pathways. In the first, glucose is released in muscles to fuel its contraction or it is released in liver to transport it in to the blood. It is catalysed by the Glycogen phosphorylase and Debranching enzyme. In the second pathway, glycogen is degraded to glucose within the lysosome by the enzyme \u03b1-glucosidase and acid maltase.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<ul>\n<li>Glycogen metabolism is very important because it facilitate the blood glucose level to be maintained between meals (liver glycogen) and also act as an energy reserve for muscular activity. The maintenanceof blood glucose is essential in order to supply energy to tissues.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-402\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-209.png\" alt=\"\" width=\"422\" height=\"249\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-209.png 422w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-209-300x177.png 300w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-209-65x38.png 65w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-209-225x133.png 225w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-209-350x207.png 350w\" sizes=\"auto, (max-width: 422px) 100vw, 422px\" \/><\/li>\n<\/ul>\n<p><strong>\u00a0 \u00a0 STEPS OF GLYCOGENOLYSIS<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Glycogenolysis requires2main enzymes. Glycogenolysisoccurs by a different pathway from glycogenesis.<\/p>\n<ol style=\"text-align: justify\">\n<li>Glucose-1-phosphate formation from non reducing end of glycogen by Glycogen phosphorylase<\/li>\n<\/ol>\n<ol style=\"text-align: justify\" start=\"2\">\n<li>Removal of \u03b1-1,6 branches from glycogen by Glycogen Debranching enzyme<\/li>\n<\/ol>\n<ol start=\"3\">\n<li style=\"text-align: justify\">Glucose-6-phosphate formation from Glucose-1-phosphateby Phosphoglucomutase.<\/li>\n<\/ol>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-403\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-210.png\" alt=\"\" width=\"531\" height=\"413\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-210.png 531w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-210-300x233.png 300w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-210-65x51.png 65w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-210-225x175.png 225w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-210-350x272.png 350w\" sizes=\"auto, (max-width: 531px) 100vw, 531px\" \/><\/p>\n<p style=\"text-align: center\"><strong>Fig: 24.2OVERVIEW OF GLYCOGENOLYSIS<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><strong>1. Glucose-1-phosphate formation from non reducing end of glycogen by Glycogen phosphorylase<\/strong><\/p>\n<ul>\n<li>Glycogen is\u00a0 broken-down\u00a0 in\u00a0 to\u00a0 Glucose-1-Phosphate\u00a0 (G1P)\u00a0 by\u00a0 Glycogen<\/li>\n<\/ul>\n<p style=\"text-align: justify\">\u00a0 \u00a0 \u00a0 \u00a0 Phosphorylase. It is carried out by\u00a0phosphorolysis reaction. Phosphorolysis\u00a0 reaction involves the cleavage of larger molecules into smaller molecules. It uses phosphate for the cleavage. Such breakdown of bonds by the addition of orthophosphate is referred to as phosphorolysis. A hydrolysis reaction also involves the same process but it uses water instead of phosphate for the cleavage of bond.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-404\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-211.png\" alt=\"\" width=\"471\" height=\"449\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-211.png 471w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-211-300x286.png 300w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-211-65x62.png 65w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-211-225x214.png 225w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-211-350x334.png 350w\" sizes=\"auto, (max-width: 471px) 100vw, 471px\" \/><\/p>\n<p style=\"text-align: center\"><strong>Fig: 24.3 Formation of G- 1-P from glycogen<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify\">Cleavage by phosphorolysis is energetically favourable because released glucose is phosphorylated. While hydrolytically release of sugar needs to be phosphorylated before enters into the glycolytic pathway.<\/li>\n<\/ul>\n<ul>\n<li style=\"text-align: justify\">Glycogen phosphorylase act on exoglycosidic bond. Pyridoxal phosphate is an necessary cofactor in the glycogen phosphorylase reaction. This cofactor is linked to lysine 680 of the enzyme.<\/li>\n<\/ul>\n<ul style=\"text-align: justify\">\n<li>Glycogen phosphorylase will act repeatedly on non-reducing ends of a glycogen chain. Glycogen phosphorylase can act continuously until it reaches 4 glucose away from \u03b1 1-6 branch point.<\/li>\n<\/ul>\n<ul style=\"text-align: justify\">\n<li>Glycogen phosphorylase is an allosteric enzyme. AMP acts as an allosteric activator while ATP, G6P and glucose acts as an allosteric inhibitor. Glycogen phosphorylase is also regulated by covalent modification. ( For further details please refer module:26 ,<span style=\"text-align: initial;font-size: 1em\"> regulation of glycogen degradation)<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"text-align: justify\">Generally in the structure of glycogen about 1 in 10 residues is branched. In such situation phosphorylase enzyme cannot degrade glycogen independently. It will stop to a halt after the release of six glucose molecules per branch.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p><strong>2. Removal of \u03b1-1,6 branches from glycogen by Glycogen Debranching enzyme<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify\">In glycogen, \u03b1- 1-6 glycosidic bonds at the branch point are not susceptible to cleavage by glycogen phosphorylase while it can act continuously until it reaches four glucose away from \u03b1 1-6 branch point. Thus further degradation of glycogen chain by glycogen phosphorylase occurs only after the action of a glycogen debranching enzyme.<\/li>\n<\/ul>\n<ul>\n<li>Glycogen debranching enzyme shows two different activities.<\/li>\n<\/ul>\n<p style=\"text-align: justify\">\u00a0 \u00a0 o Transferase activity<\/p>\n<p style=\"text-align: justify\">o \u03b1 1\u00e06 glucosidase activity<\/p>\n<ul>\n<li style=\"text-align: justify\">In transferase activity, the enzyme removes and transfers terminal 3 of the 4 glucose residues. It transfers this moiety intact to the non reducing end of another branch. It involves cleaving of an \u03b1 (1\u00e04) linkage and formation of new \u03b1 (1\u00e04) linkage in another branch. This action leaves a single<span style=\"text-align: initial;font-size: 1em\"> glucose at the \u03b11,6 branch.<\/span><\/li>\n<\/ul>\n<ul style=\"text-align: justify\">\n<li>In \u03b1 1\u00e06 glucosidase activity, enzyme removes the single glucose residue which is remaining at branch point by an alpha (1\u00e06 glucosidase activity of the same debranching enzyme.<\/li>\n<\/ul>\n<ul>\n<li style=\"text-align: justify\">91 % of the glycogen residues are converted to Glucose-1-phosphate by the combined activity of glycogen phosphorylase and glycogen debranching enzyme.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Remaining about 8 % are converted to glucose by the \u03b1 1\u00e06 glucosidase activity of the glycogen debranching enzyme.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><strong>3. Glucose-6-phosphate formation from Glucose-1-phosphate by Phosphoglucomutase<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify\">Glucose-1-phosphate is converted to Glucose-6-phosphate by Phosphoglucomutase.<\/li>\n<\/ul>\n<ul style=\"text-align: justify\">\n<li>Active site of the active Phosphoglucomutase molecule has a phosphorylated serine residue. The phosphoryl group istransferred from the amino acid serine to the hydroxyl group (C-6) of glucose 1-phosphate. It result in to<span style=\"text-align: initial;font-size: 1em\"> the formation of intermediate called glucose1, 6-bisphosphate. The phosphoryl group from the C-1\u00a0<\/span>of glucose 1, 6-bisphosphate is then transfer<span style=\"text-align: initial;font-size: 1em\"> to the serine residue of the enzyme. It results <\/span>in to<span style=\"text-align: initial;font-size: 1em\"> the formation of glucose 6-phosphate and the regeneration of the enzyme.<\/span><\/li>\n<\/ul>\n<div>\n<ul>\n<li style=\"text-align: justify\">\u00a0This reaction is reversible. It allows the inter conversion of Glucose-6-Phosphate and Glucose-1-Phosphate. This isvery important. Phosphoglucomutase is also required to form.<\/li>\n<\/ul>\n<\/div>\n<p><span style=\"text-align: initial;font-size: 1em\"><span style=\"text-align: initial;font-size: 1em\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-405\" src=\"http:\/\/biocp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/215\/2019\/04\/1-212.png\" alt=\"\" width=\"653\" height=\"292\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-212.png 653w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-212-300x134.png 300w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-212-65x29.png 65w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-212-225x101.png 225w, https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-content\/uploads\/sites\/215\/2019\/04\/1-212-350x157.png 350w\" sizes=\"auto, (max-width: 653px) 100vw, 653px\" \/><\/span><\/span><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<table>\n<tbody>\n<tr>\n<td><strong>you can view video on Glycogenolysis<\/strong><\/td>\n<td><a href=\"https:\/\/youtu.be\/NLSTHlBahcM\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-120\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"\" width=\"36\" height=\"36\" \/><\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>&nbsp;<\/p>\n<div class=\"textbox learning-objectives\">\n<h3>References<\/h3>\n<ul>\n<li style=\"text-align: justify\">Peter J. Roach, Anna A. Depaoli-Roach, Thomas D. Hurley, Vincent S. Tagliabracci (2012) Glycogen and its metabolism: some new developments and old themes . Biochemical Journal, 441 (3) 763-787; DOI: 10.1042\/BJ20111416<\/li>\n<li style=\"text-align: justify\">Roach PJ, Depaoli-Roach AA, Hurley TD, Tagliabracci VS (2012) Glycogen and its metabolism: some new developments and old themes. Biochem J 441: 763\u2013787. doi: 10.1042\/BJ20111416<\/li>\n<li style=\"text-align: justify\">Wilson WA, Roach PJ, Montero M, Baroja-Fernandez E, Munoz FJ, Eydallin G, et al. Regulation of glycogen metabolism in yeast and bacteria. Fems Microbiol Rev. 2010;34(6):952\u2013985.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p><strong>Web site<\/strong><\/p>\n<ul>\n<li>http:\/\/www.wiley.com\/college\/fob\/quiz\/quiz15\/15-20.swf<\/li>\n<li>https:\/\/www.tamu.edu\/faculty\/bmiles\/lectures\/Glycogen%20Metabolism.pdf<\/li>\n<li>http:\/\/themedicalbiochemistrypage.org\/glycogen.php<\/li>\n<li>https:\/\/en.wikibooks.org\/wiki\/Principles_of_Biochemistry<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p><strong>Books<\/strong><\/p>\n<ul>\n<li style=\"text-align: justify\">Harper\u2019sIllustrated Biochemistry by Robert K.. Murray, Daryl K. Granner, Peter A. Mayes, 26th Edition (2003)<\/li>\n<li style=\"text-align: justify\">Lehninger\u2019S Principle of Biochemistry David L. Nelson and Michael M. Cox,5th Edition (2008)<\/li>\n<li style=\"text-align: justify\">Instant Notes: Biochemistry, 2nd Edition, B.D. Hames &amp; N. M. Hooper (2005)<\/li>\n<li style=\"text-align: justify\">Textbook of Biochemistry, 4th Edition Donald Voet, Judith G. Voet(2011)<\/li>\n<\/ul>\n<p style=\"text-align: justify\">\n<\/div>\n<p>&nbsp;<\/p>\n","protected":false},"author":3,"menu_order":24,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["dr-vikram-raval"],"pb_section_license":""},"chapter-type":[],"contributor":[61],"license":[],"class_list":["post-400","chapter","type-chapter","status-publish","hentry","contributor-dr-vikram-raval"],"part":3,"_links":{"self":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/pressbooks\/v2\/chapters\/400","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/wp\/v2\/users\/3"}],"version-history":[{"count":4,"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/pressbooks\/v2\/chapters\/400\/revisions"}],"predecessor-version":[{"id":409,"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/pressbooks\/v2\/chapters\/400\/revisions\/409"}],"part":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/pressbooks\/v2\/parts\/3"}],"metadata":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/pressbooks\/v2\/chapters\/400\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/wp\/v2\/media?parent=400"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/pressbooks\/v2\/chapter-type?post=400"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/wp\/v2\/contributor?post=400"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/biocp04\/wp-json\/wp\/v2\/license?post=400"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}