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Hình 6.1. Đề án chuyển hóa glycogen và glycolysis. PGK, phosphoglycerate kinase; P, phosphate; PLD, phosphorylase hạn dextrin; UDPG, uridine diphosphate glucose. Các chữ số La Mã cho biết các enzyme có thiếu sót gây ra gan (in nghiêng) | 102 Chapter 6 The Glycogen Storage Diseases and Related Disorders Glycogen Metabolism Glycogen is a macromolecule composed of glucose units. It is found in all tissues but is most abundant in liver and muscle where it serves as an energy store pro viding glucose and glycolytic intermediates o Fig. 6.1 Numerous enzymes intervene in the synthesis and degradation of glycogen which is regulated by hormones. Epinephrine Exercise __ Glucagon cA P Ca II Protein Kinase zT J Phosphorylase b Kinase--- IX Phosphorylase a- Phosphorylase b V VI PLD II Glucose 6-P Glucose Fructose 6-P Fructose 1 6-P Glyceraldehyde 3-P 2 3-P-Glycerol Phosphate 2 I -------PGK Deficiency 3-Phosphạglycerate 2 2-Phosphoglycerate 2 Phosphoenplpyruvate 2 Pyruvate 2 Ĩ Xl Lactate 2 o Fig. 6.1. Scheme of glycogen metabolism and glycolysis. PGK phosphoglycerate kinase P phosphate PLD phosphorylase limit dextrin UDPG uridine diphosphate glucose. Roman numerals indicate enzymes whose deficiencies cause liver italics and or muscle glycogenoses 0 glycogen synthase I glucose-6-phos-phatase II acid maltase a-glucosidase III debranching enzyme IV branching enzyme V myophosphorylase VI liver phosphorylase VII phosphofructokinase IX phosphorylase-b-kinase X phosphoglycerate mutase XI lactate dehydrogenase XII fruc-tose-1 6-bisphosphate aldolase A XIII p-enolase 103 6 6.1 The Liver Glycogenoses The liver glycogen storage disorders GSDs comprise GSD I the hepatic presentations of GSD III GSD IV GSD VI the liver forms of GSD IX and GSD 0. GSD I III VI and IX present similarly with hypoglycemia marked hepatomegaly and growth retardation. GSD I is the most severe affecting both glycogen breakdown and gluconeogenesis. In GSD Ib there is additionally a disorder of neutrophil function. Most patients with GSD III have a syndrome that includes hepatopathy myopathy and often cardiomyopathy. GSD VI and GSD IX are the least severe there is only a mild tendency to fasting hypoglycemia liver size normalises with age and
