Functional characterization of enone oxidoreductases from strawberry and tomato fruit

Dorothée Klein, Barbara Fink, Beate Arold, Wolfgang Eisenreich, Wilfried Schwab

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43 Scopus citations

Abstract

Fragaria x ananassa enone oxidoreductase (FaEO), earlier putatively assigned as quinone oxidoreductase, is a ripening-induced, negatively auxin-regulated enzyme that catalyzes the formation of 4-hydroxy-2,5-dimethyl- 3(2H)-furanone (HDMF), the key flavor compound in strawberry fruit by the reduction of the α,β-unsaturated bond of the highly reactive precursor 4-hydroxy-5-methyl-2-methylene-3(2H)-furanone (HMMF). Here we show that recombinant FaEO does not reduce the double bond of straight-chain 2-alkenals or 2-alkenones but rather hydrogenates previously unknown HMMF derivatives substituted at the methylene functional group. The furanones were prepared from 4-hydroxy-5-methyl-3(2H)-furanone with a number of aldehydes and a ketone. The kinetic data for the newly synthesized aroma-active substrates and products are similar to the values obtained for an enone oxidoreductase from Arabidopsis thaliana catalyzing the α,β-hydrogenation of 2-alkenals. HMMF, the substrate of FaEO that is formed during strawberry fruit ripening, was also detected in tomato and pineapple fruit by HPLC-ESI-MSn and became 13C-labeled when D-[6-13C]-glucose was applied to the fruits, which suggested that a similar HDMF biosynthetic pathway occurs in the different plant species. With a database search (http://ted.bti.cornell.edu/ and http://genet.imb.uq.edu.au/Pineapple/), we identified a tomato and pineapple expressed sequence tag that shows significant homology to FaEO. Solanum lycopersicon EO (SIEO) was cloned from cDNA, and the protein was expressed in Escherichia coli and purified. Biochemical studies confirmed the involvement of SIEO in the biosynthesis of HDMF in tomato fruit.

Original languageEnglish
Pages (from-to)6705-6711
Number of pages7
JournalJournal of agricultural and food chemistry
Volume55
Issue number16
DOIs
StatePublished - 8 Aug 2007

Keywords

  • 4-hydroxy-2,5-dimethyl-3(2H)-furanone
  • Enone oxidoreductase
  • Flavor formation
  • Fragaria x ananassa
  • Solanum lycopersicon

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