MetaCyc Pathway: pinitol biosynthesis II
Inferred from experiment

Pathway diagram: pinitol biosynthesis II

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: BiosynthesisCarbohydrates BiosynthesisSugars BiosynthesisSugar Alcohols BiosynthesisPinitol 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

Created 02-Mar-2011 by Zhang P, TAIR


Dittrich72: Dittrich, P, Kandler, O (1972). "Biosynthesis of D-1-O-methyl-mucoinositol in gymnosperms." Phytochemistry, 1972, 11:1729-1732.

Ruis69: Ruis H, Hoffmann-Ostenhof O (1969). "Enzymic epimerization of sequoyitol to D-pinitol in Trifolium incarnatum." Eur J Biochem 7(3);442-8. PMID: 4389340

Vernon92: Vernon DM, Bohnert HJ (1992). "A novel methyl transferase induced by osmotic stress in the facultative halophyte Mesembryanthemum crystallinum." EMBO J 11(6);2077-85. PMID: 1600940

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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