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Apple flavor is characterized by combinations of ester compounds, which increase markedly during fruit ripening. The final step in ester biosynthesis is catalyzed by alcohol acyl transferases (AATs) that use coenzyme A (CoA) donors together with alcohol acceptors as substrates. The gene MpAAT1, which produces a predicted protein containing features of other plant acyl transferases, was isolated fromMalus pumila(cv. Royal Gala). TheMpAAT1gene is expressed in leaves, flowers and fruit of apple. | iFEBS Journal An alcohol acyl transferase from apple cv. Royal Gala MpAATI produces esters involved in apple fruit flavor Edwige J. F. Souleyre David R. Greenwood Ellen N. Friel Sakuntala Karunairetnam and Richard D. Newcomb The Horticulturaland Food Research Institute of New Zealand Ltd. HortResearch Auckland New Zealand Keywords aroma alcoholacyltransferase volatiles ester biosynthesis apple Malus pumila cv. RoyalGala Correspondence E. J. F. Souleyre Molecular Olfaction Group Mt Albert Research Centre The Horticulturaland Food Research Institute of New Zealand Ltd Private Bag 92169 Auckland New Zealand Fax 64 9 8154201 Tel 64 9 8154200 E-mail esouleyre@hortresearch.co.nz Received 24 January 2005 revised 5 April 2005 accepted 21 April 2005 doi 10.1111 j.1742-4658.2005.04732.x Apple flavor is characterized by combinations of ester compounds which increase markedly during fruit ripening. The final step in ester biosynthesis is catalyzed by alcohol acyl transferases AATs that use coenzyme A CoA donors together with alcohol acceptors as substrates. The gene MpAATl which produces a predicted protein containing features of other plant acyl transferases was isolated from Malus pumila cv. Royal Gala . The MpAATl gene is expressed in leaves flowers and fruit of apple. The recombinant enzyme can utilize a range of alcohol substrates from short to medium straight chain C3-C10 branched chain aromatic and terpene alcohols. The enzyme can also utilize a range of short to medium chain CoAs. The binding of the alcohol substrate is rate limiting compared with the binding of the CoA substrate. Among different alcohol substrates there is more variation in turnover compared with Km values. MpAATl is capable of producing many esters found in Royal Gala fruit including hexyl esters butyl acetate and 2-methylbutyl acetate. Of these MpAATl prefers to produce the hexyl esters of C3 C6 and C8 CoAs. For the acetate esters however MpAAT1 preference depends upon substrate concentration. At .
