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Biochemical Contributors to Exercise Fatigue
Published in Peter M. Tiidus, Rebecca E. K. MacPherson, Paul J. LeBlanc, Andrea R. Josse, The Routledge Handbook on Biochemistry of Exercise, 2020
Arthur J. Cheng, Maja Schlittler, Håkan Westerblad
Glycogen breakdown is controlled by glycogen phosphorylase, which is regulated by covalent phosphorylation, allosteric regulation, and substrate availability (44). Phosphorylase exists in two forms: a phosphorylated form (referred to as phosphorylase a) that is considered to be constitutively active and a non-phosphorylated form (referred to as phosphorylase b) that is fully dependent on AMP for activation and is considered to be essentially inactive in resting muscle (13). Phosphorylation (activation) and dephosphorylation (inactivation) of phosphorylase are catalyzed by specific kinases and phosphatases, respectively (39). Glycogen synthesis is catalyzed by glycogen synthase, and the activity of this enzyme is controlled by phosphorylation in a complex manner (72).
Medicinal Plants in Natural Health Care as Phytopharmaceuticals
Published in Anil K. Sharma, Raj K. Keservani, Surya Prakash Gautam, Herbal Product Development, 2020
Studies have demonstrated the hypoglycaemic action and effects of coriander on carbohydrate metabolism. The effect of coriander seeds on carbohydrate metabolism was studied in rats that were fed with a fat-rich cholesterol diet. The spice exhibited noteworthy hypoglycemic action. There was an increase in the concentration of hepatic glycogen as was evident from the increased activity of glycogen synthase. Activities of glycogen phosphorylase and gluconeogenic enzymes revealed decreased rates of glycogenolysis and gluconeogenesis. The increased activities of glucose-6-phosphate dehydrogenase and glycolytic enzymes suggest the utilization of glucose by the pentose phosphate pathway and glycolysis. These observations clearly indicated that coriander seeds demonstrate good hypoglycemic activity through enhanced glycogenesis, glycolysis and decreased glycogenolysis and gluconeogenesis (Aissaoui et al., 2011).
Fuel Metabolism in the Fetus
Published in Emilio Herrera, Robert H. Knopp, Perinatal Biochemistry, 2020
The pathway of glycogen synthesis in the adult is summarized in Figure 6. It involves the activation of a glycogen synthase and the inhibition of a glycogen phosphorylase by mechanisms under the dependence of insulin and glucagon through cAMP-dependent pathways. Glycogen synthase and glycogen phosphorylase exist in active and inactive forms of which interconversion is catalyzed by phosphorylation/dephosphorylation processes under the control of specific kinases and phosphatases. Dephosphorylation of these two enzymes leads to glycogen synthase activation, glycogen phosphorylase inactivation, and glycogen synthesis. Moreover, glycogen phosphorylase in its active form is an inhibitor of the glycogen synthase phosphatase, thus precluding a concomitant synthesis and degradation of glycogen. glucose itself is able to stimulate glycogen synthesis because of the activation of glycogen phosphorylase phosphatase and inhibition of glycogen phosphorylase a, which blocks glycogen breakdown and facilitates glycogen synthesis.
Platelet glycogenolysis is important for energy production and function
Published in Platelets, 2023
Kanakanagavalli Shravani Prakhya, Hemendra Vekaria, Daniёlle M. Coenen, Linda Omali, Joshua Lykins, Smita Joshi, Hammodah R. Alfar, Qing Jun Wang, Patrick Sullivan, Sidney W. Whiteheart
A key enzyme needed to mobilize glucose from glycogen is glycogen phosphorylase.4 This enzyme removes terminal, α1–4-linked, glucoses from the polymer, generating glucose-1-phosphate that can be further metabolized by glycolysis.11 Glycogen phosphorylase exists in two interconvertible forms (a and b); the proportions of each are regulated by phosphorylation.12 Pharmacological inhibitors of glycogen phosphorylase have been developed to attenuate the hyperglycemia associated with diabetes, though their success has been limited because of bleeding complications.13,14 Two structurally related compounds, CP316819 and CP91149, inhibit GP by binding at the regulatory pocket.13 CP316819 is a more efficacious derivative of CP91149. These inhibitors principally bind to the less active b form and prevent its conversion to the more active a form.
Glycogen phosphorylase B promotes cell proliferation and migration through PI3K/AKT pathway in non-small cell lung cancer
Published in Experimental Lung Research, 2021
Yiyi Zhan, Ru Chen, Tianhai Wang, Shijun Shan, Hongge Zhu
Under hypoxia condition, glycogen is the storage form of glucose in most of the tumor cells.18 Therefore, glycogen metabolism is essential for tumor cell growth under metabolic stress.19 Glycogen phosphorylases, as the rate limited enzymes in glycogen degradation, play key role in cancer progression and has evolved as new targets for cancer therapy.20 In NSCLC, glycogen phosphorylase regulates nuclear glycogenolysis, and controls epigenetic regulation for cell growth.21 Glycogen debranching enzyme, another enzyme responsible for glycogen degradation, has been reported as a critical regulator of NSCLC.22 Recently, PYGB, one of the three isoforms of glycogen phosphorylase in mammals, was shown to be highly expressed in NSCLC.23 However, the functional role as well as the mechanism of PYGB in NSCLC remain enigmatic. In this study, we investigated the impact of PYGB on NSCLC and the mechanism of PYGB contributing to proliferation, migration, and invasion.
Novel approaches for designing drugs that interfere with pH regulation
Published in Expert Opinion on Drug Discovery, 2019
Emanuela Berrino, Claudiu T. Supuran
A large number of cellular processes is strongly dependent of the intracellular pH, meaning that alteration of pH steady state has important consequences on the cell homeostasis [1,15,16]. Cellular metabolism is mutually dependent of the acid-base balance since the products generated from several metabolic pathways can affect intracellular pH, which in turn impairs the activity of metabolic enzymes. In this context, glycolytic enzymes such as the phosphofructokinase or phosphorylase are highly sensitive to pH changes, with variations of even 0.1 pH units making them catalytically inactive. Cellular contraction is also affected by intracellular acidification, probably because of a reduced cellular excitability. For the same reason, membrane electric conductance can be affected by pH modifications, by means of changes of the ion channel charge with the subsequent alteration of ion permeability. Cellular activation and proliferation are thought to be initiated by alkalinization events. In this context, the role of pH in cellular activation and proliferation was defined as ‘permissive’ rather than necessary. Finally, cell death is also strongly dependent of intracellular pH, as apoptotic enzymes such as caspase, or DNA damage checkpoints are found to be suppressed by an alkaline pHi [1,15,16] (Scheme 1).