著者

畑中 顯和 梶原 忠彦 関谷 次郎

出版者

天然有機化合物討論会実行委員会

雑誌

天然有機化合物討論会講演要旨集 22 (ISSN:24331856)

巻号頁・発行日

pp.657-664, 1979-09-20 (Released:2017-08-18)

---

Endogenous linolenic acid in Thea chloroplasts is cleaved into cis-3-hexenal and 11-formyl-cis-9-undecenoic acid via a very labile intermediate by E_2 of an enzyme system E_2 (E_2 and E'_2+E"_2) bound to the lamellae membranes of chloroplasts under aerobic condition. On the other hand, in external addition of a large amount of linoleic acid to chloroplasts, E'_2 and E"_2 activities newly are induced in addition to E_2 activity, and E'_2 catalyzes the formation of 13-Hydroperoxide and then it was cleaved to n-hexanal by E"_2. The substrate specificity of the enzyme system E_2 in Thea chloroplasts was clarified with an entire series of synthesized positional isomers, in which the position of cis-1,cis-4-pentadiene system varies from C-3 to C-13 in C_<18> fatty acid and geometrical isomers of linoleic acid. The structural requirement for the substrate of E_2 is the presence of cis-1,cis-4-pentadiene system between ω-6 and ω-10. The enantiomeric composition of the 13-Hydroperoxide produced by E'_2 was determined by GLC and NMR analysis: After a large amount of linoleic acid was incubated with tea chloroplasts, a mixture of hydroperoxides (13-hydroperoxy-cis-9,trans-11-/9-hydroperoxy-trans-10,cis-12-octadecadienoic acid=84/16: crude-I) was isolated. The major hydroperoxide of the crude-I was identified as 13-L-hydroperoxy-cis-9,trans-11-octadecadienoic acid (80) containing a small amount of its enantiomer(13-D=20). So, it was demonstrated that E'_2in Tea chloroplasts catalyzes the stereospecific oxygenation of linoleic acid to the 13-L-hydroperoxide.