ISSN:
1432-2048
Keywords:
Cyclitol biosynthesis
;
myo-Inositol 6-O-methyltransferase
;
Ononitol
;
Vigna
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The cyclitol 1d-4-O-methyl-myo-inositol (d-ononitol) is accumulated in certain legumes in response to abiotic stresses. S-Adenosyl-l-methionine:myo-inositol 6-O-methyltransferase (m6OMT), the enzyme which catalyses the synthesis of d-ononitol, was extracted from stems of Vigna umbellata Ohwi et Ohashi and purified to apparent homogeneity by a combination of conventional chromatographic techniques and by affinity chromatography on immobilized S-adenosyl-l-homocysteine (SAH). The purified m6OMT was photoaffinity labelled with S-adenosyl-l-[14C-methyl]methionine. The native molecular weight was determined to be 106 kDa, with a subunit molecular weight of 40 kDa. Substrate-saturation kinetics of m6OMT for myo-inositol and S-adenosyl-l-methionine (SAM) were Michaelis-Menten type with K m values of 2.92 mM and 63 μM, respectively. The SAH competitively inhibited the enzyme with respect to SAM (K i of 1.63 μM). The enzyme did not require divalent cations for activity, but was strongly inhibited by Mn2+, Zn2+ and Cu2+ and sulfhydryl group inhibitors. The purified m6OMT was found to be highly specific for the 6-hydroxyl group of myo-inositol and showed no activity on other naturally occurring isomeric inositols and inositol O-methyl-ethers. Neither d-ononitol, nor d-3-O-methyl-chiro-inositol, d-1-O-methyl-muco-inositol or d-chiro-inositol (end products of the biosynthetic pathway in which m6OMT catalyses the first step), inhibited the activity of the enzyme.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00196663
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