Dehydrogenases fructose dehydrogenase

As discussed in Section 22.7, illumination of chloroplasts leads to light-driven pumping of protons into the thylakoid lumen, which causes pH changes in both the stroma and the thylakoid lumen (Figure 22.27). The stromal pH rises, typically to pH 8. Because rubisco and rubisco activase are more active at pH 8, COg fixation is activated as stromal pH rises. Fructose-1,6-bisphosphatase, ribulose-5-phosphate kinase, and glyceraldehyde-3-phosphate dehydrogenase all have alkaline pH optima. Thus, their activities increase as a result of the light-induced pH increase in the stroma. 

Directed evolution of enzymes has been used to improve the reducing function of the enzymes. For example, this method was used to eliminate the cofactor requirement of B. stearothermophillus lactate dehydrogenase, which is activated in the presence of fructose 1,6-bisphosphate [12]. The activator is expensive and representative of the sort of cofactor complications that are undesirable in industrial processes. Three rounds of random mutagenesis and screening produced a mutant that is almost fully... 

Figure 17.12 Direct electrocatal3ftic oxidation of D-fnictose at a glassy carbon electrode painted with a paste of Ketjen black particles modified with D-fructose dehydrogenase from a Gluconobacter species. The enzyme incorporates an additional heme center allowing direct electron transfer from the electrode to the flavin active site. Cyclic voltammograms were recorded at a scan rate of 20 mV s and at 25 + 2 °C and pH 5.0. Reproduced by permission of the PCCP Owner Societies, from Kamitaka et al., 2007.

Ameyama M. 1982. Enzymatic microdetemtination of D-glucose, D-fructose, D-gluconate, 2-keto-D-gluconate, aldehyde, and alcohol with memhrane-hound dehydrogenases. Meth Enzymol 89 20-29. 

Fructose dehydrogenase (FDH) having pyrroloquinoline quinone (PQQ) as a prosthetic group is an redox enzyme to catalyze the oxidation of fructose. A... 

Fig. 11 Differential pulse voltammogram of the molecularly interfaced fructose dehydrogenase (—) and simply adsorbed one...

Electron Transfer Type of Dehydrogenase Sensors To fabricate an enzyme sensor for fructose, we found that a molecular interface of polypyrrole was not sufficient to realize high sensitivity and stability. We thus incorporated mediators (ferricyanide and ferrocene) in the enzyme-interface for the effective and the most sensitive detection of fructose in two different ways (l) two step method first, a monolayer FDH was electrochemically adsorbed on the electrode surface by electrostatic interaction, then entrapment of mediator and electro-polymerization of pyrrole in thin membrane was simultaneously performed in a separate solution containing mediator and pyrrole, (2) one-step method co-immobilization of mediator and enzyme and polymerization of pyrrole was simultaneously done in a solution containing enzyme enzyme, mediator and pyrrole as illustrated in Fig.22. 

In clinical chemistry however, these systems have not been differentiated as yet. Since the oxidation of an alcohol corresponds to the reduction of a ketose or an aldose, the designations ketose reductase and aldose reductase, respectively, were suggested (H4, W14). In this paper however, the enzyme or enzyme system will be named polyol or sorbitol dehydrogenase (SDH), although the latter expression does not characterize exacdy the enzyme s function in a general biochemical sense. But sorbitol or fructose have been commonly used as substrates in clinical chemical investigations. 

Aldolase 4.1.2.3 C Fructose-1,6-diphosphate NADH Glyceraldehyde-3- phosphate Glycerophosphate dehydrogenase... 

Glucose phosphate isomerase 5.3.1.9 C Fructose-6- phosphate NADP+ Glucose-6- phosphate Glucose-6-phosphate dehydrogenase... 

The natural substrate for the dehydrogenase, glyceraldehyde-3-phosphate (G-3-P), had been synthesized earlier by Hermann Fischer, Emil Fischer s son, and Baer in 1932. In 1934 Meyerhof and Lohmann synthesized hexose diphosphate, establishing it to be fructose 1,6 bisphosphate (F-l, 6 bis P). With F-1,6 bisP as substrate and hydrazine to trap the aldehydic and ketonic products of the reaction, G-3-P was identified in the mixture of G-3-P and dihydroxyacetone phosphate which resulted. Triose phosphate isomerase was then isolated and the importance of phosphorylated 3C derivatives established. 

Figure 6.3 Multienzymatic activity test for FSA. G3P D-glyceraldehyde-3-phosphate F6P fructose-6-phosphate PGI phosphoglucose Isomerase G6P glucose-6-phosphate GPD glu-cose-6-phosphate dehydrogenase.

Fructose 6-P NADH Formation Glucosephosphate Isomerase, Glucose-6-P Dehydrogenase Fructokinase ... 

This enzyme [EC 1.1.1.14], also known as L-iditol 2-dehydrogenase and polyol dehydrogenase, catalyzes the reaction of L-iditol with NAD+ to produce L-sorbose and NADH. The enzyme will also convert D-glucitol to D-fructose. 

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