Glucose 6-phosphate dehydrogenase, enzymatic

For the synthesis of vanillin itself, there follows, in a separate step, a further enzymatic reduction ofthe carboxylic function. To recover the NADP+, the reaction product is stirred for 7 hours at 30 °C together with glucose in the presence of the arylaldehyde-dehydrogenase from Neurospora crassa and glucose phosphate dehydrogenase. 

C18. Cross, R. T., Hurwitz, R. E., and Marks, P. A., An hereditary enzymatic defect in erythrocyte metabolism Glucose-6-phosphate dehydrogenase deficiency. J. Clin. Invest. 37, 1170-1184 (1958). 

H. J. Engel, W. Domschke, M. Alberti, and G. F. Domagk, Protein structure and enzymatic activity II. Purification and properties of a crystalline glucose-6-phosphate dehydrogenase from Candida utilis, Biochim. Biophys. Acta, 191, 509-522 (1969). 

Figure 15-2 Absorption spectra of NAD+ and NADH. Spectra of NADP+ and NADPH are nearly the same as these. The difference in absorbance between oxidized and reduced forms at 340 nm is the basis for what is probably the single most often used spectral measurement in biochemistry. Reduction of NAD+ or NADP+ or oxidation of NADH or NADPH is measured by changes in absorbance at 340 nm in many methods of enzyme assay. If a pyridine nucleotide is not a reactant for the enzyme being studied, a coupled assay is often possible. For example, the rate of enzymatic formation of ATP in a process can be measured by adding to the reaction mixture the following enzymes and substrates hexokinase + glucose + glucose-6-phosphate dehydrogenase + NADP+. As ATP is formed, it phosphorylates glucose via the action of hexokinase. NADP+ then oxidizes the glucose 6-phosphate that is formed with production of NADPH, whose rate of appearance is monitored at 340 nm.

The first method of enzymatic PolyP assay was proposed by Clark et al. (1986). In this technique, PolyPs were determined by polyphosphate glucokinase obtained from Pro-pionibacterium shermanii. Glucose-6-phosphate dehydrogenase reduced NADP through utilization of the formed glucose-6-phosphate, and the increase in NADPH concentration was measured. 

Enzymatic reactions that cannot be monitored directly by spectroscopic changes can be coupled to other reactions that do show such changes. One of the classic examples is the detection of glucose by an assay which depends on its conversion by hexo-kinase into glucose 6-phosphate, which is then coupled to an ancillary indicator reaction with NADP+ and glucose 6-phosphate dehydrogenase ... 

As discussed above, an enzymatic reaction is usually found to be more rapid in one direction than the other so that the reaction is virtually irreversible.If the product of the reaction in one direction is removed as it is formed (Le., because it is the substrate of a second enzyme present in the reaction mixture), the equilibrium of the first enzymatic process is displaced so that the reaction may continue to completion in that direction. Reaction sequences in which the product of one enzyme-catalyzed reaction becomes the substrate of another enzyme, often through many stages, are characteristic of metabolic processes. Analytically, several enzymatic reactions also may be Unked together to provide a means of measuring the activity of the first enzyme or the concentration of the initial substrate in the chain. For example, the activity of creatine kinase is usually measured by a series of linked reactions, and glucose can be determined by consecutive reactions catalyzed by hexokinase and glucose-6-phosphate dehydrogenase. 

Deficiencies of any of these red cell enzymes may result in impaired ATP generation and consequently loss of function of the erythrocyte. By far the majority of these disorders are hereditary in nature, although acquired deficiencies have been described, mainly in malignant disorders involving the bone marrow. Hereditary enzymatic defects in these pathways disturb the erythrocyte s integrity, shorten its cellular survival, and produce chronic nonspherocytic hemolytic anemia (CNSHA). Deficiencies of some enzymes, however, do not lead to chronic hemolytic anemia, but to acute episodes of severe hemolysis when there is increased oxidative stress on the red cell (as in some types of glucose-6-phosphate dehydrogenase deficiency). 

Using the glucose-6-phosphate dehydrogenase (G6PDH) enzymatic sub-system as an example, reaction rate of G6PDH (i.e., rate of reaction facilitated by G6PDH) is given as ... 

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