BIOSYNTHESIS OF P-HYDROXYPHENYLBUTAN-2-ONE IN RASPBERRY FRUITS AND TISSUE-CULTURES

p-Hydroxyphenylbutan-2-one (pHPB), the raspberry ketone, is responsibl e for the characteristic aroma of raspberries. The compound accumulate s rapidly during the later maturation stages of the berries. The synth esis and accumulation of pHPB correlates with that of anthocyanin and soluble solids (Brix). pHPB is synthesized in cell-free extracts of fr uits and tissue cultures from p-coumaryl-CoA and malonyl-CoA in a mann er similar to the synthesis of chalcones and stilbenes. The specific b iosynthetic pathway for pHPB formation deviates from the general pheny lpropanoid pathway at the p-coumaryl-CoA stage and it is composed of t wo enzymes. The first enzyme is the p-hydroxyphenylbut-3-ene-2-one syn thase (pHPB-3-ene-2-one synthase) that forms p-hydroxyphenylbut-3-ene- 2-one by the condensation of malonyl-CoA with p-coumaryl-CoA. The seco nd enzyme, p-hydroxyphenylbut-3-ene-2-one reductase (pHPB-3-ene-2-one reductase), reduces the p-hydroxyphenylbut-3-ene-2-one to p-hydroxyphe nylbutan-2-one, the raspberry ketone. We detected the activity of both enzymes in crude extracts from raspberry fruits and their tissue cult ures, and identified their reaction products by HPLC, crystallization to constant radioactivity and by GC-MS.