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Published in Samar Razaq, Difficult Cases in Primary Care, 2021
McArdle’s syndrome is another glycogen storage disease, resulting in inefficient use of energy substrate in muscle due to muscle phosphorylase deficiency. Exercise results in cramp that tends to settle with a period of rest. Creatine kinase levels may be elevated. It is generally a benign disorder and may not even be picked up until later in adult life when the individual takes up strenuous exercise. No specific treatment exists but the patient should be advised to stop exercise on the onset of muscle cramps. Failure to do so may result in rhabdomyolysis, myoglobinuria and subsequent renal failure.
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).
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.
Is the benefit of using adjuvant capecitabine in patients with residual triple-negative breast cancer related to pathological response to neoadjuvant chemotherapy?
Published in Expert Review of Anticancer Therapy, 2022
Özgecan Dülgar, Başak Bala Öven, Muhammed Mustafa Atcı, Rukiye Arıkan, Seval Ay, Murat Ayhan, Oğuzhan Selvi, Deniz Tataroglu Ozyukseler, Ertuğrul Bayram, Erkan Özcan, Ayşe İrem Yasin, Mahmut Gümüş
Poor responsive group included patients with tumor with no change or minimal loss of tumor cellularity after anthracycline and taxane therapy. We can suspect chemotherapy resistance in the unresponsive group. Despite chemotherapy resistance, capecitabine improves the survival outcomes of patients in the poor response group. Capecitabine activity depends on thymidine phosphorylase enzyme expression that converts capecitabine to cytotoxic fluorouracil in tumors. Thymidine phosphorylase is highly expressed in breast cancer and up-regulated by taxanes and cyclophosphamide and by X-ray irradiation [13]. In our study, 91.1% and 88.5% of patients received adjuvant radiotherapy (RT) in poor and good response group, respectively. While the adjuvant single agent capecitabine is ineffective, post-neoadjuvant use increases the efficacy of capecitabine. In Geicam/2003-10 trial, cyclophosphamide was omitted in the experimental capecitabine arm, and the study failed to show improvement with the addition of adjuvant capecitabine despite large cohort and long follow up [14].
Ameliorative effects of tropisetron on liver injury in streptozotocin-induced diabetic rats
Published in Archives of Physiology and Biochemistry, 2021
Shiva Gholizadeh-Ghaleh Aziz, Roya Naderi, Nima Mahmodian
Insulin enhances intracellular glycogen deposition which triggers glycogen synthase and inhibits glycogen phosphorylase. Therefore, as shown in this study, glycogen contents decrease in some tissues, including the liver (Whitton and Hems 1975) in insulin deficiency such as STZ injection. In the present study, tropisetron ameliorated the reduction of liver glycogen content in STZ-induced T1DM. Heimes et al. (2009) reported that tropisetron can increase insulin secretion in an insulin-producing beta cell line in vitro. Thus, the glycogen accumulation effect of tropisetron in diabetic animals seems logical. Interestingly, no significant difference was observed in the glycogen content of the glibenclamide-administered and tropisetron-administered groups in the liver of diabetic rats.