Carotenoids Carvone

With regard to the metabolism of primary carotenoid degradation p ucts, recent results obtained by Tang and Suga (57) have indicated a two-step mechanism for the conversion of the primary carotenoid metabolite B-ionone 1 to 14 in Nicotiana tabacum plant cells (cf. Fig. 4). These results revealed, that first of all, the side-chain double bond is hydrogenated by the action of carvone reductase (co-factor NADH), before the carbonyl function is enzymatically reduced in the second step. Importantly, the enantioselectivity of the latter reductase is decisive for the enantiomeric composition in fruits as outlined for theaspirane formation from the labile precursor diol 12 (cf. Fig. 5). The formation of vitispiranes 10, edulans 11 and related Ci3-norisoprenoids (29,30) is known to proceed via similar mechanisms. 

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