Dehydrogenases polyol dehydrogenase

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. 

Further studies on liver polyol dehydrogenases (e.g., Hll, Mil, T3, W14, W19) revealed the existence of a number of enzymes catalyzing reactions which can be written as follows ... 

Different preparative procedures have been shown to yield protein fractions which are able to catalyze different types of reactions with respect to their requirement of either NAD or NADP as coenzymes [cf. Eqs. (19), (20), and (21)]. In sera of mice poisoned by carbon tetrachloride we found polyol dehydrogenases catalyzing the oxidation of the following polyols (a) with NAD sorbitol, ribitol, mannitol (b) with NADP sorbitol, ribitol. Erythritol and mt/o-inositol were not attacked at all. Figures 8 and 9 show the results of these determinations performed at pH 9.6. In the NAD system sorbitol and ribitol are oxidized at exactly the same rate, while in the NADP system ribitol does not reach the rate of sorbitol. The ratio NAD NADP for sorbitol is calculated to be 4.20 and for ribitol 5.50. Mannitol is oxidized at 23% of the rate of sorbitol. 

The reactivity of xylitol in the polyol dehydrogenase reactions has been extensively studied for its relations to pentosuria. Xylitol was found to be oxidized in two ways (a) to L-xylulose by a highly specific NADP-requiring dehydrogenase and (b) to D-xylulose by a NAD-linked enzyme with lesser substrate specificity ... 

Fic. 8. NAD polyol dehydrogenase in sera of CCl4-poisoned mice sorbitol, ribitol, and mannitol oxidation (pH 9.6 polyols as substrates). 

The evidence that polyol dehydrogenases can be considered as a group of different enzymes is supported by the finding that all reactions exhibit a specific stereochemical pattern (e.g., Mil, S13, V3). 

The role that polyol dehydrogenases play in metabolism has scarcely been elucidated. Approaches were made by investigating the metabolic fate of C14-labeled sorbitol after oral and parenteral administration. It has been found that in normal animals C1402 was expired following the administration of labeled sorbitol, while eviscerated, liverless subjects showed no C1402 expiration under these conditions, thus confirming... 

Clinical Implications of Polyol Dehydrogenases 5.6.1. Serum SDH Activity in Disease States... 

The Role of Polyol Dehydrogenases in Essential Congenital Pentosuria... 

Hll. Hollman, S., and Touster, O., The L-xylulose-xylitol enzyme and other polyol dehydrogenases of guinea pig liver mitochondria. ]. Biol. Chem. 225, 87-102 (1957). 

Dehydrogenase, 6-Phosphogluconate Dehydrogenase, Glutathione Reductase, Methemoglobin Reductase, Polyol Dehydrogenases (Bruns and Werners), 5, 237... 

This enzyme [EC 1.1.1.21], also known as aldehyde reductase and polyol dehydrogenase (NADP ), catalyzes the reaction of an alditol with NAD(P) to generate an aldose and NAD(P)H. The enzyme exhibits a broad specificity for the alditol. 

ACTIN ASSEMBLY KINETICS POLYNUCLEOTIDE S -HYDROXYL-KINASE POLYNUCLEOTIDE PHOSPHORYLASE Polyol dehydrogenase,... 

Schematic of the polyol pathway showing the NADPH-dependent reduction of open chain D-glucose to sorbitol, which is catalyzed by ALR2. This step is followed by the NAD+-dependent oxidation of sorbitol by sorbitol dehydrogenase to yield D-fructose.

A random urine sample can be used for the analysis of polyols. TALDO and RPI deficiencies, as well as galactosaemia and presumably sorbitol dehydrogenase deficiency, can be diagnosed using urine. The samples are stored frozen. Repeated freeze-thawing does not influence the concentrations of the polyols. 

Figure 6.5. Compatibility of organic osmolytes with enzyme function. (Upper panel) Pyruvate kinase of the marine crab Pachygrapsus crassipes. The effects of KC1 and NaCI and several organic solutes on the Km of phosphoenol pyruvate (PEP) (modified after Bowlus and Somero, 1979). (Middle panel) Malate dehydrogenase of the mangrove (Rhizophora mangle). Effects of NaCI and three organic osmolytes (the amino acid proline and the polyols pinitol and OMMI) on catalytic activity (modified after Sommer et al., 1990). (Bottom panel) Effects of NaCI and four osmolytes found in mammalian kidney (urea, glycine betaine, sorbitol, and inositol) on the Km of uric acid of uricase (modified after Yancey, 1992). (Figure modified after Somero and Yancey, 1997.)...

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