Hexokinase activation

Hexene, mass spectrum of, 415 Hexokinase, active site in. 163... 

Figure 7-10. Coupled enzyme assay for hexokinase activity. The production of glucose 6-phosphate by hexokinase is coupled to the oxidation of this product by glucose-6-phosphate dehydrogenase in the presence of added enzyme and NADP". When an excess of glucose-6-phosphate dehydrogenase is present, the rate of formation of NADPH, which can be measured at 340 nm, is governed by the rate of formation of glucose 6-phosphate by hexokinase.

L6. Lehto, M., Huang, X., Davis, E. M Le Beau, M. M., Laurila, K. F., Eriksson, K. F., Bell, G. I., and Groop, L., Human hexokinase II gene Exon-intron organization, mutation screening in N1DDM, and its relationship to muscle hexokinase activity. Diabetologia 38, 1466-1474 (1995). 

Hormones have a profound effect on carbohydrate metabolism. Great interest has been aroused by reports of hormonal control of hexokinase activity by specific proteins in animal tissues.99- 100 Hexokinase action is the rate-limiting step in the uptake of D-glucose by muscle. Hexokinase is inhibited in diabetic muscle, but the inhibition can be partially reversed by insulin. A protein fraction from the anterior pituitary gland will inhibit the hexokinase of extracts of brain and muscle, and the effect of this... 

The introduction of the invertase from yeast alone was not sufficient. Invertase cleaves sucrose to release the two component sugars, glucose and fructose. While fructose can be readily metabolized by fructokinase in potato tubers, there is insufficient hexokinase activity in developing potato tubers to bring the glucose into intermediary metabolism. Therefore, it was necessary to introduce a second transgene, a bacterial glucokinase, in order to ensure that the hexoses became available for subsequent metabolism.25... 

FIGURE 15-36 Control of glycogen synthesis from blood glucose in myocytes. Insulin affects three of the five steps in this pathway, but it is the effects on transport and hexokinase activity, not the change in glycogen synthase activity, that increase the flux toward glycogen. 

In the absence of added glucose, hexokinase was found to catalyze the very slow hydrolysis of MgATP (59). This has been explained by assuming that water has replaced glucose at the active site of the enzyme. This ATPase activity can be inhibited by compounds that inhibit the hexokinase activity (60) and can be stimulated by compounds such as D-xylose or D-lyxose which lack the terminal -CH2OH of glucose (61). The ATPase reaction has been used to support evidence that hexokinase has a random kinetic mechanism, since it shows that ATP can bind to hexokinase in the absence of glucose (62). 

Exley et al. [61] found aluminum in practically all reagents used in a study of the inhibition of hexokinase activity by this element. The way to overcome the problem was cleaning the solutions using an aminophosphonate chelation resin. The procedure reduced the contamination of ATP and NADP to approximately 5% and 10% of their initial values, respectively, but the resin was ineffective in removing aluminum from magnesium acetate or the enzyme glucose 6-phosphate dehydrogenase. Probably the conditions were not favorable for the resin to pick up the aluminum ions from these solutions. It is important to remember that, if there is an affinity between aluminum and the species in solution, a competition between this species and the resin will take place. 

Hepatoma, transhydrogenase in, 65 Hexokinase, activity in muscle, 47 Histidine residues... 

Dovrat, A., Horwitz, J., Sivak, J.G., Weinreb, O., Scharf, J., and Silbermann, M. (1993) DL-propranolol inhibits lens hexokinase activity and affects lens optics, Exp. Eye. Res., 57, 747-751. 

Fluorodeoxyglucose is the most commonly used radiotracer for imaging glucose utilization. The uptake of FDG into tissues is determined mainly by high glucose transporter and hexokinase activities and low... 

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