Biosynthesis of Acyl Moieties of Capsaicin and its Analogues from Valine and Leucine in Capsicum Fruits

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Biosynthetic pathways of acyl moieties of capsaicinoid in intact Capsicum fruits and spheroplasts prepared from placentas of Capsicum fruits were examined using a radioisotopic technique. In intact Capsicum fruits, L-[U-^<14>C] valine was incorporated into capsaicin and dihydrocapsaicin, the acyl constituents of which are even-number branched chain fatty acids, while L-[U-^<14>C] leucine was incorporated into nordihydrocapsaicin and homodihydrocapsaicin, which have odd-number branched chain fatty acids as the. acyl moieties. The intermediates of the odd- and even-number branched chain fatty acids were identified with GLC/GPC after the spheroplasts had been incubated with L-[U-^<14>C] valine or L-[U-^<14>Cl leucine. After incubation with L-[U-^<14>C] valine, isobutyric acid and 8-methyl nonanoic acid were detected, while isopentanoic acid and 9-methyl decanoic acid were found after incubation with L-[U-^<14>C] leucine. The involvement of α-ketoisovalerate or α-ketoisocaproate in the biosynthesis of acyl moieties of capsaicinoid was also demonstrated in vitro using cell-free extracts of the placentas of Capsicum fruits. These findings suggest that the acyl moieties of individual capsaicinoid in Capsicum fruits are synthesized by pathways similar to those proposed for adipose tissue and bacteria.
日本植物生理学会の論文