Hexokinase and

Another simple sugar that enters glycolysis at the same point as fructose is mannose, which occurs in many glycoproteins, glycolipids, and polysaccharides (Chapter 7). Mannose is also phosphorylated from ATP by hexokinase, and the mannose-6-phosphate thus produced is converted to fructose-6-phosphate by phosphomannoisomerase. 

Acifluorfen, synthesis of, 683 Acrolein, structure of, 697 Acrylic acid, pKa of, 756 structure of. 753 Activating group (aromatic substitution), 561 acidity and, 760 explanation of, 564-565 Activation energy, 158 magnitude of, 159 reaction rate and, 158-159 Active site (enzyme), 162-163 citrate synthase and, 1046 hexokinase and, 163... 

Coe and Bessell and coworkers studied the metabolic fates of 2-deoxy-2-fluoro-D-glucose (2DFG) and related compounds by using yeast hexokinase (as a model for mammalian hexokinase), and determined the kinetic constants K and V ) of the Michaelis-Menten equation D-glucose 0.17 (K in mAf)> 1 00 (relative value, D-glucose taken as 1) 2DG 0.59 0.11, 0.85 2DFG 0.19 0.03, 0.50 2-deoxy-2-fluoro-D-mannose (2DFM) 0.41 0.05, 0.85 2-deoxy-2,2-difluoro-D-nraZ>//Jo-hexose... 

Allow for consumption of ATP by reactions catalyzed by hexokinase and phosphofructokinase... 

Figure 19-5. Variation in glucose phosphorylating activity of hexokinase and glucokinase with increase of blood glucose concentration. The for glucose of hexokinase is 0.05 mmol/L and of glucokinase is 10 mmol/L.

The names of enzymes usually end in -ase, for example hexokinase and nitrogenase. 

A kinetic procedure employing the reverse reaction is coupled to the enzymes hexokinase and glucose-6-phosphate dehydrogenase, as used by Nielson and Ludvigson after the method of Oliver (J ). This procedure was later modified and optimized by Rosalki (38). 

Brain hexokinase is inhibited by its product glucose-6-phosphate and to a lesser extent by adenosine diphosphate. The isoenzyme of hexokinase found in brain may be soluble in the cytosol or be attached firmly to mitochondria [2 and references therein]. An equilibrium exists between the soluble and the bound enzyme. The binding changes the kinetic properties of hexokinase and its inhibition by Glc-6-P resulting in a more active enzyme. The extent of binding is inversely related to the ATP ADP ratio, i.e. conditions in which energy utilization... 

Several different changes in mitochondria occur during apoptosis. These include a change in membrane potential (usually depolarization), increased production of reactive oxygen species, potassium channel activation, calcium ion uptake, increased membrane permeability and release of cytochrome c and apoptosis inducing factor (AIF) [25]. Increased permeability of the mitochondrial membranes is a pivotal event in apoptosis and appears to result from the formation of pores in the membrane the proteins that form such permeability transition pores (PTP) may include a voltage-dependent anion channel (VDAC), the adenine nucleotide translocator, cyclophilin D, the peripheral benzodiazepine receptor, hexokinase and... 

Mannose, fructose and glucose may all be assayed independently using hexokinase and the appropriate additional enzymes. All the reactions can be monitored by the increase in absorbance at 340 nm as NADI is reduced to NADPH. 

Treatment of 9-(/ -D-ribofuranosyluronic acid)adenine with diphenylphosphoro-chloridate and orthophosphate or tripolyphosphate yields (62) and (63), which, although unstable, inhibit rabbit AMP aminohydrolase and pyruvate kinase, respectively, with behaviour characteristic of active-site-specific reagents.98 Adenylate kinases from several sources are inactivated by iV6-[2- and 4-fluorobenzoyl]-adenosine-5 -triphosphates, with kinetics characteristic of active-site labelling, although these compounds were without effect on yeast hexokinase and rabbit pyruvate kinase.99... 

Two examples are presented the hexokinase and phos-phoglucoisomerase reaction in glycolysis (data taken from experiments with the isolated perfused rat heart). 

There are two different glucose-phosphorylating enzymes, hexokinase and glucokinase, which catalyse the reaction ... 

Initial phosphorylations The formation of fructose bisphosphate occurs via two phosphorylation reactions that involve ATP hydrolysis, which are catalysed by hexokinase and phosphofructokinase ... 

The physiological usefulness of this method for identifying the fuels that are used and their rates of utilisation in different cells is discussed in other chapters (Chapter 3). For example, measurement of the activity of the enzymes hexokinase and glutaminase in immune cells showed, for the first time, that glucose and glutamine are the major fuels utilised by these cells. This finding has had clinical significance (Chapter 17). 

ATP NADH Disappearance Hexokinase and Glucose-6-P Dehydrogenase Adenylate Kinase, Creatine Kinase ... 

For this reason, these alternative routes for isotope combination with enzyme-substrate and/or enzyme-product complexes ensures that raising the [A]/[Q] or [B]/[P] pair will not depress either the A< Q or the B< P exchanges. Fromm, Silverstein, and Boyer conducted a thorough analysis of the equilibrium exchange kinetic behavior of yeast hexokinase, and the data shown in Fig. 2 indicate that there is a random mechanism of substrate addition and product release. 

The reacting enzyme centrifugation technique has been used with yeast hexokinase and with phosphoenolpy-ruvate carboxykinase. ... 

Creatine phosphokinase activity has been reported to be minimally inhibited by hemolysis. Hemoglobin concentrations of 1.25 g/100 ml inhibit 5% and 2.5 g/100 ml, 12% (N5). However, in methods utilizing adenosine diphosphate in the reaction mixture, hemolysates containing 100 mg of hemoglobin per 100 ml may have apparent activities of 5-100 units/liter. The activity is presumably related to adenylate kinase in the erythrocyte (S33). In methods utilizing adenosine diphosphate in a coupled enzyme reaction with hexokinase and glucose-6-phosphatase, the inhibitory effect can be eliminated by adding sufficient adenosine mono-... 

B. Two key enzymes, hexokinase and glucokinase, catalyze the reaction of glucose with ATP to form glucose 6- ph osphate, which becomes trapped in the cell and subject to metabolism. 

Hexokinase 280 kU/l/glucose-6-phosphate dehydrogenase 140 kU/1 hexokinase and glucose-6-phosphate dehydrogenase from yeast, suspended in 3.2 M ammonium sulfate solution. Dilute stock solutions with 3.2 M ammonium sulfate solution according to specified activity to 280 kU/1 and 140 kU/1, respectively. 

Smith, T.A. (2000) Mammalian hexokinases and their abnormal expression in cancer. Br. J. Biomed. Sci. 57, 170-178. 

Effect of glucose concentration on the rate of phosphorylation catalyzed by hexokinase and glucokinase. 

Some enzymes, such as yeast hexokinase and creatine kinase (Chapter 12), associate in extremely asymmetric ways.102 A dimer is formed by means of heterologous interactions but steric hindrance prevents the unsatisfied sets of interacting groups from joining with additional monomers to form higher polymers. 

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