Enzymes glucose-6-phosphate dehydrogenase

In this biosensor a quartz radio crystal is functionalized with the enzyme glucose-6-phosphate dehydrogenase. As shown in Figure 3, a thin film of Pmssian blue [14038-43-8] C gN gFe, is then coated onto the crystal. 

Third, a poly[bis(phenoxy)phosphazene] has been coated on porous alumina particles, surface nitrated, reduced to the amino-derivative, and then coupled to the enzyme glucose-6-phosphate dehydrogenase or trypsin by means of glutaric dialdehyde. The immobilized enzymes were more stable than their counterparts in solution, and they could be used in continuous flow enzyme reactor equipment (25). 

The importance of having adequate supplies of NADPH for the regeneration of these various enzymes cannot be over emphasized. In normal situations this cofactor can be adequately provided by the reductive pentose phosphate pathway. Monitoring the activity of the pentose phosphate pathway has been proposed as a unique way to study the metabolic response to oxidative stress, since the glutathione peroxidase activity is coupled via glutathione reductase to the enzyme glucose-6-phosphate dehydrogenase (Ben Yoseph et ah, 1994). 

K8. Kerppola, W., Nikkila, E. A., and Pitkanen, E., Serum TPN linked enzymes glucose-6-phosphate dehydrogenase, isocitric dehydrogenase and glutathione reductase activities in health and various disease states. Acta Med. Scand. 164, 357-305 (1959). 

Another enzyme used for the measurement of glucose is hexokinase (EC 2.7.1.1) which catalyses the phosphorylation of glucose to produce glucose-6-phosphate with adenosine triphosphate as the phosphate donor and magnesium ions as an activator. The rate of formation of glucose-6-phosphate can be linked to the reduction of NADP by the enzyme glucose-6-phosphate dehydrogenase (EC 1.1.1.49). This indicator reaction can be monitored spectrophotometrically at 340 nm or fluorimetrically ... 

Oxidized, denatured hemoglobin forms aggregates, which can become attached to the inner surface of the red cell, known as Heinz bodies. This leads to damage to the red cell, which may result in direct destruction of the cell, which can be shown in vitro, or removal from the circulation by the spleen in vivo. When caused by Fava beans, the syndrome is known as Favism. As the deficient enzyme (glucose-6-phosphate dehydrogenase) is intrinsic to the red cell, exposure of such cells in vitro to suitable drugs will lead to cell damage and death. 

The simple cases where one enzyme is employed afford a limited scope of potential targets. Usually two or more enzyme reactions are coupled, as exemplified by the development of a piezoelectrically-transduced biocatalytic biosensor that couples two enzyme reactions to detect glucose [492-62-6], C6H120 > (3) (13). In this biosensor a quartz radio crystal is functionalized with the enzyme glucose-6-phosphate dehydrogenase. As shown in Figure 3, a thin film of Prussian blue [14038 43-8], C18N18Fe7, is then coated onto the crystal. 

Figure 3.20 Plots showing the activity of the enzyme, glucose-6-phosphate dehydrogenase as a function of time for (open circles) the free enzyme in solution and (black circles) the enzyme bound to the surface of poly[W.v(phcnoxy)phosphazene]. The polyphosphazene is an excellent surface substrate because of the stability of the polymer backbone to nitration and reduction, and the ease with which the hydrophobicity or hydrophilicity of the surface can be changed. From Allcock and Kwon, reference 191.

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. 

It is becoming increasingly evident that a number of adverse reactions to drugs are due to genetically transmitted inborn enzyme abnormalities or deficiencies. The best known example of this category is the hereditary relative deficiency of the enzyme glucose-6-phosphate-dehydrogenase (G-6-PD), which occurs in 5% to 10% of Mediterranean littoral races, blacks, Pakistanis, and Sephardic Jews. This condition renders affected individuals susceptible to acute hemolytic ane-... 

This reaction involves nicotinamide adenine dinucleotide phosphate (NADP), in the presence of its specific enzyme, glucose-6-phosphate dehydrogenase (G6PDH). 

Umbilical cord blood is deficient in the enzyme glucose-6-phosphate dehydrogenase and thus cannot readily convert the methemoglobin that is formed "naturally" back to hemoglobin as is readily done in adults. 

A more common genetic defect was also described in which the enzyme glucose-6-phosphate dehydrogenase has decreased activity (Goldstein et al. 1969). The pattern of inheritance of this trait is linked to one of several alleles on the X chromosome. The phenotype is expressed as an incomplete dominant trait. Thus, female heterozygotes are not known to have severely depressed enzyme levels and males may have a wide range of activity. These phenotypes express a wide... 

Isolation and subcloning of two key enzymes, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, from the thermophile Thermotoga maritima... 

Fig. 36.4. Regulation of citrate lyase, malic enzyme, glucose 6-phosphate dehydrogenase, and fatty acid synthase. Citrate lyase, which provides acetyl CoA for fatty acid biosynthesis, the enzymes that provide NADPH (malic enzyme, glucose 6-phosphate dehydrogenase), as well as fatty acid synthase, are inducible (circled t).

The main control of flux in the oxidative pentose phosphate pathway under normal conditions is the profound product inhibition by NADPH on the first enzyme, glucose-6-phosphate dehydrogenase (G6PDH). NADPH concentrations can become low due to active lipogenesis. Then G6PDH will increase in activity. 

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