Sterol glycosyltransferases catalyze the synthesis of diverse glycosterols in plants. Withania somnifera is a medically important plant, known for a variety of pharmacologically important ...withanolides and their glycosides. In this study, a novel 27beta-hydroxy glucosyltransferase was purified to near homogeneity from cytosolic fraction of W. somnifera leaves and studied for its biochemical and kinetic properties. The purified enzyme showed activity with UDP-glucose but not with UDP-galactose as sugar donor. It exhibited broad sterol specificity by glucosylating a variety of sterols/withanolides with beta-OH group at C-17, C-21 and C-27 positions. It transferred glucose to the alkanol at C-25 position of the lactone ring, provided an alpha-OH was present at C-17 in the sterol skeleton. A comparable enzyme has not been reported earlier from plants. The enzyme is distinct from the previously purified W. somnifera 3beta-hydroxy specific sterol glucosyltransferase and does not glucosylate the sterols at C-3 position; though it also follows an ordered sequential bisubstrate reaction mechanism, in which UDP-glucose and sterol are the first and second binding substrates. The enzyme activity with withanolides suggests its role in secondary metabolism in W. somnifera. Results on peptide mass fingerprinting showed its resemblance with glycuronosyltransferase like protein. The enzyme activity in the leaves of W. somnifera was enhanced following the application of salicylic acid. In contrast, it decreased rapidly on exposure of the plants to heat shock, suggesting functional role of the enzyme in biotic and abiotic stresses.
Sterol glycosyltransferases catalyze the synthesis of diverse glycosteroids in plants, leading to a change in their participation in cellular metabolism. Withania somnifera is a medically important ...plant, known for a variety of pharmacologically important withanolides and their glycosides. In this study, a cytosolic sterol glucosyltransferase was purified 3406 fold to near homogeneity from W. somnifera leaves and studied for its biochemical and kinetic properties. The purified enzyme was active with UDP-glucose but not with UDP-galactose as sugar donor. It exhibited broad sterol specificity by glucosylating a variety of sterols and phytosterols with 3beta-OH group. It showed a low level of activity with flavonoids and isoflavonoids. The enzyme gave maximum K(cat)/K(m) value (0.957) for 24-methylenecholesterol that resembles aglycone structure of pharmacologically important sitoindosides VII and VIII from W. somnifera. The enzyme follows ordered sequential bisubstrate mechanism of reaction, in which UDP-glucose and sterol are the first and second binding substrates. This is the first detailed kinetic study on purified plant cytosolic sterol glucosyltransferases. Results on peptide mass fingerprinting and substrate specificity suggested that the enzyme belongs to the family of secondary metabolite glucosylating glucosyltransferases. The enzyme activity exhibited a rapid in vivo response to high temperature and salicylic acid treatment of plants, suggesting its physiological role in abiotic and biotic stress.
Transgenic cultivars expressing delta -endotoxin coding genes of Bacillus thuringiensis are being grown globally on about 12 million hectares this year. Agriculture in India can benefit substantially ...by adopting transgenic insecticidal cultivars since, in contrast to the world average of 30%, of the total chemical pesticides used in India 75% are employed against insects. No other biological approach, as safe as and yet as effective as the Bt technology is presently known to control agricultural pests. The question at the center stage is to expedite the commercial release of Bt transgenics and also make a parallel effort to devise knowledge-based strategies aimed at achieving longer durability of crop resistance to insect pests. Plant breeders have encountered similar situations in the past for improving crops against insects and other diseases. This article identifies the gap areas where research efforts are needed to develop strategies for enhancing the durability of crop resistance.
Silver(I) dialkyl/alkylene dithiophosphates of the types Ag{S^sub 2^P(OR)^sub 2^} and Ag{S^sub 2^P(OGO)} (where R = -Pr^sup n^; G = -CMe^sub 2^CH^sub 2^CHMe-, -CH^sub 2^CMe^sub 2^CH^sub 2^-, -CMe^sub ...2^CMe^sub 2^- or -CH^sub 2^CH^sub 2^CHMe-) have been prepared by treating an aqueous solution of AgNO^sub 3^ with ammonia salts of the respective dithiophosphoric acid. The derivatives form 1:1 adducts readily with 2,2'-bipyridine or Ph^sub 3^P in CH^sub 2^Cl^sub 2^ solution. These novel complexes have been characterized by elemental analyses, molecular weight measurements and spectral (i.r., ^sup 1^H- and ^sup 31^P-n.m.r.) studies. The crystal structure of Ag{S^sub 2^POCH^sub 2^CMe^sub 2^CH^sub 2^O · PPh^sub 3^^sub 2^ · 2H^sub 2^O exhibits an unsymmetrical attachment of the silver(I) to the ligand moiety.PUBLICATION ABSTRACT
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