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Cell Physiology
Published in Wei-Shou Hu, Cell Culture Bioprocess Engineering, 2020
Glucose from the medium is imported into cells via the glucose transporter. During glycolysis, high-energy compounds (ATP and NADH) are generated. However, the first segment of glycolysis actually consumes two ATP for each glucose (Figure 3.2, Panel 3.3). The two ATP are used to add a phosphate group to each end of the glucose molecule. The first phosphorylation converts glucose to glucose 6-phosphate (G6P). After isomerization to fructose 6-phosphate (F6P), the second phosphate is added to give fructose 1,6-bisphosphate (F16BP). The two phosphate groups, being nucleophilic centers, help pull their surrounding electron clouds toward the two ends of the molecule, thereby making the carbon-carbon bond in the middle of the glucose molecule susceptible to enzymatic cleavage (Figure 3.3). The six-carbon F16BP becomes two three-carbon compounds: glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone-phosphate (DHAP). These two compounds are interconvertible through a reversible reaction. The continued utilization of GAP toward downstream reactions effectively draws DHAP toward GAP. The original 1 mole of glucose now becomes 2 moles of GAP and moves further downstream in glycolysis. The conversion of 2 GAP to the end product of 2 pyruvates also converts 2 NAD+ and 4 ADP to 2 NADH and 4 ATP. The net energetic consequence of the conversion of glucose to 2 pyruvate in glycolysis is the generation of 2 ATP (recall 2 ATP are consumed to activate glucose) and 2 NADH. Note that NAD+ is often denoted as NAD in the text.
Applications of Chemical Kinetics in Environmental Systems
Published in Kalliat T. Valsaraj, Elizabeth M. Melvin, Principles of Environmental Thermodynamics and Kinetics, 2018
Kalliat T. Valsaraj, Elizabeth M. Melvin
The synthesis of pyruvic acid by the partial oxidation of glucose is called “glycolysis.” This reaction is a convenient one to show how ATP mediates in a metabolic process. Shown in Figure 4.51 is the partial oxidation process. The process starts with the conversion of glucose to glucose-6-phosphate in which one ATP molecule is lost. Subsequent rearrangement to fructose-6-phosphate and loss of another ATP gives fructose-1,6-diphosphate. At this point, there is a net energy loss. However, during further transformations, two molecules of ATP are gained and hence overall energy is stored during the process. The conversion of glyceraldehyde-3-phosphate to pyruvic acid is the most energy-yielding reaction for anaerobic organisms. This ATP/ADP cycle is called the “fermentative mode” of ATP generation and does not involve any electron transport.
Construction of Enzyme Biosensors Based on a Commercial Glucose Sensor Platform
Published in Krzysztof Iniewski, Biological and Medical Sensor Technologies, 2017
Here, the developments of two types of ATP biosensors are described which are based on new combinations of enzymes and electrodes by using the coimmobilizations of HBH, G6PDH, and HEX on a Clark-type oxygen electrode and on a screen-printed electrode. The schematic illustrations for the biosensor setup and the determination principles are shown in Figure 6.4. HEX transfers the phosphate group from ATP to glucose to form glucose-6-phosphate. G6PDH catalyzes the specific dehydrogenation of glucose-6-phosphate by consuming NADP+. The product “NADPH” initiates the irreversible hydroxylation of p-hydroxybenzoate by HBH to consume dissolved oxygen and generate 3,4-dihydroxybenzoate. During the measurement of ATP, a detectable signal caused by the consumption of oxygen by HBH can be monitored at −0.6 V versus Ag/AgCl by the Clark-type electrode, and another detectable signal caused by the generation of 3,4-dihydroxybenzoate by HBH can be monitored at 0.42 V versus Ag/AgCl by the screen-printed electrode. The electronic signals are monitored and processed with a potentiostat, and the data acquisitions are performed with a computer.
Comparative assessment of blood glucose monitoring techniques: a review
Published in Journal of Medical Engineering & Technology, 2023
Nivad Ahmadian, Annamalai Manickavasagan, Amanat Ali
Hexokinase is a glycolytic enzyme that promotes the transition process of glucose to glucose-6-phosphate (G-6-P) by utilising the energy from adenosine triphosphate (ATP) that provides the phosphate group. In the presence of magnesium ions, glucose is converted to glucose-6-phosphate (G-6-P) and adenosine diphosphate (ADP) [17]. In the next stage, G-6-P oxidises nicotinamide adenine dinucleotide phosphate (NADP) to reach the reduced form (NADPH) [18]. The final substance is 6-phosphogluconic acid. The hexokinase-based glucose detection method utilises spectrophotometry (Figure 2). NADPH strongly absorbs a particular wavelength of ultraviolet (UV) light at 340 nm, which is the main target in the monitoring of the HK method [17,18]. NADPH’s absorption value directly relates to the glucose concentration level, making this method a standard laboratory technique [19]. The detection process is prolonged according to several enzyme reaction chains [17,18,20].
Role of key enzymes in the production of docosahexaenoic acid (DHA) by Thraustochytrium sp. T01
Published in Preparative Biochemistry & Biotechnology, 2023
D. Muthu, C. Kabilan, Sathyanarayana N. Gummadi, Anju Chadha
The glucose-6-phosphate dehydrogenase activity was assayed by measuring NADPH formation. 10 µg protein concentration of the cell-free extract was added to the reaction mix containing 34 mM tris-chloride buffer, 0.85 mM glucose-6-phosphate, and 6.8 mM magnesium chloride (MgCl2). The mix was made up to 1 ml by adding water. The reaction was initiated by adding 68 µM NADP+. The sample was then spectrophotometrically analyzed using UV-VIS spectroscopy (Jasco V530) for the rate of increase in absorbance at 340 nm. One unit (U) of enzyme activity is the amount of enzyme required to reduce 1 µmol of NADP+ per minute.[27]