Aroma biosynthesis in strawberry: s-adenosylmethionine:furaneol o-methyltransferase activity in ripening fruits.
Among the most important volatile compounds in the aroma of strawberries are 2,5-dimethyl-4-hydroxy-3(2H)-furanone (Furaneol) and its methoxy derivative (methoxyfuraneol, mesifuran). Three strawberry varieties, Malach, Tamar, and Yael, were assessed for total volatiles, Furaneol, and methoxyfuraneol. The content of these compounds sharply increased during fruit ripening, with maximum values at the ripe stage. An enzymatic activity that transfers a methyl group from S-adenosylmethionine (SAM) to Furaneol sharply increases during ripening of strawberry fruits. The in vitro generated methoxyfuraneol was identified by radio-TLC and GC-MS. The partially purified enzyme had a native molecular mass of approximately 80 kDa, with optimum activity at pH 8.5 and 37 degrees C. A high apparent K(m) of 5 mM was calculated for Furaneol, whereas this enzyme preparation apparently accepted as substrates other o-dihydroxyphenol derivatives (such as catechol, caffeic acid, and protocatechuic aldehyde) with much higher affinities (K(m) approximately 105, 130, and 20 microM, respectively). A K(m) for SAM was found to be approximately 5 microM, regardless of the acceptor used. Substrates that contained a phenolic group with only one OH group, such as p-coumaric and trans-ferulic acid, as well as trans-anol and coniferyl alcohol, were apparently not accepted by this activity. It is suggested that Furaneol methylation is mediated by an O-methyltransferase activity and that this activity increases during fruit ripening.
Lavid
Noa
N
Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30-095, Israel.
Schwab
Wilfried
W
Kafkas
Ebru
E
Koch-Dean
Margery
M
Bar
Einat
E
Larkov
Olga
O
Ravid
Uzi
U
Lewinsohn
Efraim
E
D002855:Chromatography, Thin Layer; D005638:Fruit / Q000201:enzymology*; D005663:Furans / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006863:Hydrogen-Ion Concentration; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D009812:Odorants; D027824:Rosaceae / Q000201:enzymology*; D013379:Substrate Specificity
D005663:Furans; C463487:S-adenosylmethionine furaneol O-methyltransferase; C058427:furaneol; D008780:Methyltransferases