NADPH-dependent aldose reductase

Sorbitol, a sugar alcohol, is a minor dietary constituent. It can be synthesized in the body from glucose by NADPH-dependent aldose reductase (Figure 15-16). It is clinically... 

Besides the involvement in the de novo biosynthesis of BH4, SR may also participate in the pterin salvage pathway by catalyzing the conversion of sepiapterin (Figure 14, 47) into 7,8-dihydrobiopterin (46) that is then transformed to BH4 by dihydrofolate reductase (DHFR EC 1.5.1.3). Both reactions consume NADPH. Although SR is sufficient to complete the BH4 biosynthesis, a family of alternative NADPH-dependent aldo—keto reductases, including carbonyl reductases (CR), aldose reductases (AR), and the 3a-hydroxysteroid dehydrogenase type 2 (AKR1C3) may participate in the diketo reduction of the carbonyl side chain in Moreover, based on the discover) of the autosomal recessive deficiency for SR, which presents... 

A NADPH-dependent PGF, synthase activity has been partially purified from lung. Structurally, this enzyme is a member of the aldose reductase family of proteins. There is also a glutathione-dependent form of the enzyme [15]. The roles of these proteins in PGF synthesis in vivo remain to be established. 

Information about the L-arabinose pathway in yeast is rare. It is probably similar to the mold pathway. It requires a xylitol dehydrogenase as shown by Shi et al. 24). In a mutant of Pichia stipitis, which was unable to grow on L-arabinose, overexpression of a xylitol dehydrogenase could restore growth on L-arabinose. In a study of Dien et al. (5) more than 100 yeast species were tested for L-arabinose fermentation. Most of them produced arabinitol and xylitol indicating that the yeast pathway is indeed similar to the pathway of molds and not to the pathway of bacteria. There is only little knowledge of the enzymes in the yeast pathway. Aldose reductases which are active with L-arabinose and D-xylose were described e.g. for the yeasts S. cerevisiae 25) and P. stipitis 17). The enzymes have similar affinity toward D-xylose and L-arabinose and convert both sugars with a similar rate. The S. cerevisiae enzyme however is strictly NADPH-dependent, while the P. stipitis enzyme can use both NADH and... 

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