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Precise Preparation of Functional Polysaccharides Nanoparticles by an Enzymatic Approach
Published in Raj K. Keservani, Anil K. Sharma, Rajesh K. Kesharwani, Drug Delivery Approaches and Nanosystems, 2017
Phosphorylase is the enzyme that catalyzes the reversible phosphorolysis of α(1→4)-glucans at the nonreducing end, such as starch and glycogen, in the presence of Pi to produce α-D-glucose 1-phosphate (Glc-1-P) (Figure 4.4a). Depending on the reaction conditions, phosphorylase catalyzes the enzymatic glucosylation using Glc-1-P as a glycosyl donor to form α(1→4)-glucosidic linkage (Figure 4.4a). As glycosyl acceptors, oligo-α(1→4)-glucans, that is, maltooligosaccharides, are used. In the glycosylation, accordingly, a glucose residue is transferred from Glc-1-P to the nonreducing end of a maltooligosaccharide to produce the α(1→4)-glucan chain with one larger DP. Phosphorylases specifically have the smallest DP value in α(1→4)-glucan chains to recognize depending on their sources, and accordingly, maltooligosaccharides with DPs higher than the smallest one should be used as glycosyl acceptors. The smallest substrates for phosphorolysis and glycosylation recognized by phosphorylase isolated from potato (potato phosphorylase) are maltopentaose (Glc5) and maltotetraose (Glc4), respectively. On the other hand, those for the former and latter reactions recognized by phosphorylase isolated from thermophilic bacteria sources (thermostable phosphorylase) are Glc4 and maltotriose (Glc3), respectively (Boeck and Schinzel, 1996; Takaha et al., 2001; Yanase et al., 2005, 2006). These observations suggest the different recognition specificities of phosphorylases for the substrates depending on their sources.
Naturally Occurring Polymers—Plants
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
In animals, glycogen degradation to give the glucose needed as an energy source or to increase the blood sugar concentration begins with the action of phosphorylase. Phosphorylase occurs in active, a, and inactive, b, forms. Phosphorylase b is converted into phosphorylase a by phosphorylation that occurs at the end of a series of events initiated by an increased intercellular concentration of cAMP and activation of the protein kinase (Figure 10.7). This is reversed by a phosphoprotein phosphatase whose activity is hormonally regulated. Thus, phosphorylation initiated by increased intracellular concentrations of cAMP inactivates glycogen synthetase and activates phosphorylase. This is an example of the complex steps that are carried out all of the time in our bodies. Here, enzymes that are responsible for the glycogen metabolism do not act directly on glycogen but regulate the activity of other enzymes.
Intermittent fasting and probiotics in non-alcoholic fatty liver in rats: interplay between FGF19 and FGF21
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Yomna M yehya, Zeinab H. El-Said, Mohamed Adel, Basma H Othman, Atef A Mansour, Sabry M Gad
HFD led to a significant rise in the HOMA IR score with no obvious effect of PR, which is consistent with Duseja et al., 2019 [22]. However, HOMA IR was improved after IF, in line with a previous study by Baumeier et al. (2015) [23]. Fasting is thought to be similar to aerobic exercise in many physiological effects [24], as it regulates insulin and glucose tolerance despite the continuation of the diet by increasing insulin receptor sensitivity and stimulating glucose uptake by muscle and liver cells by insulin [25]. Increased β cell survival, enhanced nuclear expression of the pancreatic regeneration marker, attenuated hepatic insulin signaling, and decreased expression of glycogen phosphorylase may all contribute to this impact via restoring autophagic flux in islets [26]. Unexpectedly, IP showed no significant improvement as compared to either IF or PR alone, in agreement with previous studies by Tay et al., 2020, and Mohamad Nor et al., 2021 [27,28].
Engineered production of pyridoxal 5′-phosphate in Escherichia coli BL21
Published in Preparative Biochemistry & Biotechnology, 2022
Min He, Jian Ma, Qingwei Chen, Qili Zhang, Ping Yu
PLP is the most widely used organic cofactor in biology and is used by a variety of enzymes.[2–6] It is the coenzyme of more than 140 enzymes, which plays a wide and important role in organisms.[7] Except for glycogen phosphorylase, almost all PLP- dependent enzymes are related to the biochemical pathways of amino compounds (mainly amino acids). PLP participates in a series of reactions, such as intracellular catalytic displacement, transamination, decarboxylation, and racemization.[8] In mammals, the biosynthesis of some neurotransmitters, such as γ-aminobutyric acid, dopamine, histamine, and 5-hydroxytryptamine, is closely related to the catalysis of PLP-dependent enzymes.[9,10] PLP is also used as the coenzyme for cystathionine synthetase,[11] threonine synthetase,[12] cystathionine lyase,[13] and other enzymes. PLP plays an important role in the metabolism of phosphatidylcholine and polyunsaturated fatty acids.[14] It also affects the synthesis and function of steroid hormone receptors.[15] PLP is involved in the normal growth and development of the plant because it is essential to maintain the normal material transport and signal transduction among plant cells,[16] and has a protective effect on the roots of the plant.[17]
Acute caffeine supplementation and live match-play performance in team-sports: A systematic review (2000–2021)
Published in Journal of Sports Sciences, 2022
Adriano Arguedas-Soley, Isobel Townsend, Aaron Hengist, James Betts
Peripheral effects of caffeine on skeletal muscle contraction and fatigue also involve an interference with calcium uptake and storage in the sarcoplasmic reticulum of striated muscle, an increased calcium ion (Ca++) translocation through the plasma membrane of muscle cells and an increased myofilament Ca++ sensitivity (Nehlig et al., 1992); thus optimising myofibrillar contractions. Further, clinical studies have proposed that ingesting caffeine before exercise can enhance lipolysis via inhibition of phosphodiesterase, along with direct effects on muscle glycogen sparing via inhibition of glycogen phosphorylase (Da Silva et al., 2018). Caffeine may also increase phosphorylation of AMP-activated protein kinase (AMPK) and enhance GLUT4 translocation to the plasma membrane of muscle cells and glycogen synthase (GS) activation, which can improve AMPK-dependent glucose uptake in skeletal muscle (Jensen et al., 2007). These factors may facilitate a decreased reliance on muscle glycogen as a metabolic fuel during exercise and simultaneously increase non-esterified fatty acid (NEFA) oxidation for energy provision (Arciero et al., 1995). Together, mechanisms at the central and peripheral level may therefore culminate in greater motor unit recruitment and power output, a delayed onset of fatigue and/or a decreased perception of effort with caffeine intake before endurance or high-intensity exercise. As such, caffeine is widely used as a supplement to improve sports performance.