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Muscle Disorders
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Kourosh Rezania, Peter Pytel, Betty Soliven
Autosomal recessive disorder characterized by postexertional cramps or weakness. The gene for myophosphorylase (PYGM) maps to chromosome 11q13. It is caused by a myophosphorylase (α-1, 4-glucan orthophosphate glycosyltransferase) deficiency, which results in impaired conversion of glycogen to glucose-1-phosphate in muscle.
Functions of the Liver
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Glycogen formation from glucose-6-phosphate proceeds via glucose-1-phosphate. Glycogen synthase uses energy from uridine triphosphate to phosphorylate glucose-1-phosphate to build up glycogen polymers. With feeding, insulin is secreted in response to an increase in portal blood sugar, and this enhances glucose phosphorylation, activates glycogen synthetase, increases glycolysis, stimulates pyruvate dehydrogenase activity with increased acetyl coenzyme A (CoA) formation and inhibits glycogenolysis and gluconeogenesis. In humans, glycogen arises mainly from lactate and, to a lesser extent, from pyruvate, glycerol and gluconeogenic amino acids. Glycogen may also arise from fructose, via triose phosphates. Overall, about 10% of dietary glucose is converted to glycogen.
Galactosemia
Published in William L. Nyhan, Georg F. Hoffmann, Aida I. Al-Aqeel, Bruce A. Barshop, Atlas of Inherited Metabolic Diseases, 2020
William L. Nyhan, Georg F. Hoffmann, Aida I. Al-Aqeel, Bruce A. Barshop
The ideal approach to diagnosis of galactosemia is through routine neonatal screening. A protocol for the screening and management of galactosemia is given in Table 57.2. The assay in the United States is for the activity of galactose-1-phosphate uridyltransferase in dried blood on filter paper. In some countries, the assay is for galactose, and this will also detect galactokinase deficiency. The test for galactose will also be positive in patients with congenital shunts from portal to systemic vessels [68]. A positive screening test is confirmed by quantification of activity in freshly obtained erythrocytes in the fluorimetric assay for NADPH formed along with glucose-6-phosphate from the glucose-1-phosphate product. In classic galactosemia, the activity approximates zero. Variants with greater activity than this can be elucidated by electrophoresis or by mutational analysis. It is important for clinicians to recognize the early clinical manifestation of galactosemia and its infectious complications, because some developed countries have given up neonatal screening for this disease, and even in screened infants, classical disease can develop before the results of screening are known. The screening assay is followed by quantification of activity in freshly obtained erythrocytes.
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.
Proteomic response in Streptococcus gordonii DL1 biofilm cells during attachment to salivary MUC5B
Published in Journal of Oral Microbiology, 2021
Carolina Robertsson, Gunnel Svensäter, Zoltan Blum, Magnus E Jakobsson, Claes Wickström
The proteins that were less abundant in biofilms grown on MUC5B compared to LDP were NifU, FtcD, GALE, Phgdh, putative transcriptional regulator SGO_1758, and four uncharacterized proteins, SGO_0264, SGO_0356, SGO_0636 and SGO_0834. GALE is an isomerase that catalyzes the reaction UDP-galactose → UDP-glucose, the final step of the Leloir galactose metabolism pathway. UDP-glucose is then cycled back to the third step of the pathway, where it is converted into glucose-1-phosphate, the first intermediary of glycolysis, and then shunted into the central carbon metabolism [27]. GALE is necessary for continued Leloir pathway cycling [60]. In S. gordonii and Streptococcus sanguinis, Leloir pathway UDP-glucose is also utilized in the biosynthesis of cell surface presented polysaccharide coaggregation receptors [61]. The lower abundance of GALE suggests that UDP-galactose may be less utilized in the biofilms on MUC5B, leading to attenuated acid production and thereby a reduced risk for harmful acidification of the biofilm, and possibly also that different types of attachment strategies than the cell surface receptors produced from Leloir pathway UDP-glucose could be preferred in biofilms on MUC5B.
Neuropathological profile of the pentylenetetrazol (PTZ) kindling model
Published in International Journal of Neuroscience, 2018
E. Samokhina, Alexander Samokhin
In the meantime, Franke and Kittner [73] observed arrangement of astrocytes around capillaries in PTZ kindling. This may be related to some protection mechanisms against the above-mentioned reduction of brain glucose accessibility in epileptic tissues and, so, presents some functional benefit. When glucose intake is reduced below immediate requirements, as occurs during the period of seizure, glycogen from astrocytes was metabolized in the form of glucose-1-phosphate to ensure supply of glucose to neurons and astrocytes. Furthermore, astrocytes are key elements for the recycling and regulation of neurotransmitters, i.e. glutamate re-uptake, glutamate–glutamine shuttle, and GABA metabolism [92,93]. Astrocytic glutamine synthetase was partially inhibited after repeated PTZ-induced seizures [89]. Therefore, impaired astrocytes may contribute to an altered recycling of neurotransmitters after PTZ treatment.