This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Sugars Biosynthesis → Sugar Alcohols Biosynthesis → Pinitol Biosynthesis|
Some taxa known to possess this pathway include : Trifolium incarnatum
Expected Taxonomic Range: Viridiplantae
Pinitol is a methylated cyclic sugar alcohol (cyclitol). It has been found in bacteria, fungi, algae and plants. It plays an important role in osmoregulation and osmoprotection. In the salt-tolerant plant M. crystallinum (common ice plant), pinitol can accumulate up to 70% of total soluble carbohydrate, or 10% of plant dry weight under water stress conditions. In salt-tolerant plants pinitol was found located in the cytosol and chloroplast. In angiosperms, pinitol biosynthesis proceeds via ononitol (1D-4-O-methyl myo-inositol) [Vernon92], whereas in gymnosperms, it proceeds via sequoyitol (1D-5-O-methyl myo-inositol) [Dittrich72].
Epimerization of sequoyitol to pinitol proceeds via a keto intermediate, D-5-O-methyl-2,3,5/4,6-pentahydroxycyclohexanone. The conversion of sequoyitol to the keto intermediate was catalyzed by a NAD-specific dehydrogenase activity, whereas the conversion of the keto to pinitol was catalyzed by a NADP-dependent dehydrogenase activity. In Trifolium incarnatum, both enzyme activities were detected in a partially purified protein fraction from leaves, however the authors were not able to distinguish between the possibilities of the two activities being reside in one protein or in two proteins [Ruis69].
Variants: pinitol biosynthesis I
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