title: Hexokinase and not glycogen synthase controls the flux through the glycogen synthesis pathway in frog oocytes.
abstract: Here we set out to evaluate the role of hexokinase and glycogen synthase in the control of glycogen synthesis in vivo. We used metabolic control analysis (MCA) to determine the flux control coefficient for each of the enzymes involved in the pathway. Acute microinjection experiments in frog oocytes were specifically designed to change the endogenous activities of the enzymes, either by directly injecting increasing amounts of a given enzyme (HK, PGM and UGPase) or by microinjection of a positive allosteric effector (glc-6P for GS). Values of 0.61 ± 0.07, 0.19 ± 0.03, 0.13 ± 0.03, and -0.06 ± 0.08 were obtained for the flux control coefficients of hexokinase EC 2.7.1.1 (HK), phosphoglucomutase EC 5.4.2.1 (PGM), UDPglucose pyrophosphorylase EC 2.7.7.9 (UGPase) and glycogen synthase EC 2.4.1.11 (GS), respectively. These values satisfy the summation theorem since the sum of the control coefficients for all the enzymes of the pathway is 0.87. The results show that, in frog oocytes, glycogen synthesis through the direct pathway is under the control of hexokinase. Phosphoglucomutase and UDPG-pyrophosphorylase have a modest influence, while the control exerted by glycogen synthase is null.
authors.affiliation: Department of Biology, Faculty of Sciences, University of Chile, Las Palmeras 3425, Ñuñoa, Santiago, Chile. apreller@uchile.cl
authors.forename: Ana
authors.initials: A
authors.lastname: Preller
authors.forename: Christian A M
authors.initials: CA
authors.lastname: Wilson
authors.forename: Diego
authors.initials: D
authors.lastname: Quiroga-Roger
authors.forename: Tito
authors.initials: T
authors.lastname: Ureta
mesh_terms: D000818:Animals; D001001:Anura; D053898:Biosynthetic Pathways; D002478:Cells, Cultured; D005260:Female; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis*; D006006:Glycogen Synthase / Q000502:physiology*; D006593:Hexokinase / Q000502:physiology*; D008845:Microinjections; D009865:Oocytes / Q000201:enzymology* / Q000378:metabolism; D010733:Phosphoglucomutase / Q000502:physiology
chemical_list: D019298:Glucose-6-Phosphate; D006003:Glycogen; D006006:Glycogen Synthase; D006593:Hexokinase; D010733:Phosphoglucomutase
keywords: Flux control coefficient; Frog oocyte; GS; Glycogen synthase; HK; Hexokinase; MCA; Metabolic control analysis; PGM; UDPglucose pyrophosphorylase (EC 2.7.7.9); UPGase; glycogen synthase (EC 2.4.1.11); hexokinase (EC 2.7.1.1); metabolic control analysis; phosphoglucomutase (EC 5.4.2.1)