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Author: search.filters.author.Sharma, PankajSubject: search.filters.subject.Acetyltransferase

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    Coherent ontogenic dynamics of geraniol acetyltransferase activity and geranyl acetate concentration in flowers and leaves of aroma grass Cymbopogon martinii var. Motia
    (Springer, 2009) Sharma, Pankaj
    We have investigated the correlation between the concentration of geranyl acetate (GA) and acetyl CoA: geraniol acetyltransferase (GAAT) activity in palamarosa (Cymbopogon martini var. Motia) inflorescence and leaves at their different physiological stages. The results on GA concentration and the GAAT activity have been expressed on per gram fresh weight, per spikelet pair or leaf and per unit area of the phylloplane also incase of leaf. The percentage of geranyl acetate and geraniol in the volatile oil has also been considered. GA concentration was found to be highest in unopened floral spikelets and on the decline in fully open spikelets matching the trend of GAAT activity. Similarly, highest concentration of GA and maximum GAAT activity were found in leaves at mid-stage of development (stage II). The regression analysis curve between GA concentration (mg gFw−1) and GAAT activity (IU 10−3 gFw−1) gave an estimate of correlation coefficient (at 95% confidence) value of 0.79 for flowers and 0.92 for leaf. The results suggest that volatile ester (like geranyl acetate) synthesis in foliage and flowers of the aroma oil plant is controlled by the existent catalytic levels GAAT rather than the availability of geraniol. The study also indicates that the GAAT to be a good target to over-express for improvement of oil quality in terms of GA linked to fruit-fresh olfactory note of the oil.
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    Biochemical characteristics of a novel vegetative tissue geraniol acetyltransferase from a monoterpene oil grass (Palmarosa, Cymbopogon martinii var. Motia) leaf
    (Elsiever, 2013-04) Sharma, Pankaj
    Plants synthesize volatile alcohol esters on environmental insult or as metabolic induction during flower/fruit development. However, essential oil plants constitutively produce them as the oil constituents. Their synthesis is catalyzed by BAHD family enzymes called alcohol acyltransferases (AATs). However, no AAT has been characterized from plant foliage synthesizing acyclic monoterpenoids containing essential oils. Therefore, we have purified and biochemically characterized a geraniol: acetyl coenzyme A acetyltransferase (GAAT) from Palmarosa aroma grass (Cymbopogon martinii) leaf. MALDI-assisted proteomic study of the 43 kDa monomeric enzyme revealed its sequence motif novelties e.g. relaxed conservation at Phe and Trp in DFGWG’. This suggests permissiveness of variations in the conserved motif without loss of catalytic ability. Also, some new conserved/semi-conserved motifs of AATs were recognized. The GAAT kcat/Km values (300–700 M−1 s−1) were low (a generic characteristic for secondary metabolism enzyme) but higher than those of some floral AATs. Wide substrate acceptability for catalyzing acetylation of diverse primary alcohols (chain of ≥C6) implied its catalytic description as a ‘primary aliphatic alcohol acetyltransferase’. It signifies metabolic ability to deliver diverse aroma esters, should the acceptor alcohols be available in planta. To our knowledge, this is the first report of detailed kinetics of a vegetal monoterpenol acyltransferase