出版社：American Society for Biochemistry and Molecular Biology
摘要：Linoleate dioxygenase-cytochrome P450 (DOX-CYP) fusion enzymes are common in pathogenic fungi. The DOX domains form hydroperoxy metabolites of 18:2 n -6, which can be transformed by the CYP domains to 1,2- or 1,4-diols, epoxy alcohols, or to allene oxides. We have characterized two novel allene oxide synthases (AOSs), namely, recombinant 8 R -DOX-AOS of Coccidioides immitis (causing valley fever) and 8 S -DOX-AOS of Zymoseptoria tritici (causing septoria tritici blotch of wheat). The 8 R -DOX-AOS oxidized 18:2 n -6 sequentially to 8 R -hydroperoxy-9 Z ,12 Z -octadecadienoic acid (8 R -HPODE) and to an allene oxide, 8 R (9)-epoxy-9,12 Z -octadecadienoic acid, as judged from the accumulation of the α-ketol, 8 S -hydroxy-9-oxo-12 Z -octadecenoic acid. The 8 S -DOX-AOS of Z. tritici transformed 18:2 n -6 sequentially to 8 S -HPODE and to an α-ketol, 8 R -hydroxy-9-oxo-12 Z- octadecenoic acid, likely formed by hydrolysis of 8 S (9)-epoxy-9,12 Z -octadecadienoic acid. The 8 S -DOX-AOS oxidized [8 R -2H]18:2 n -6 to 8 S -HPODE with retention of the 2H-label, suggesting suprafacial hydrogen ion and oxygenation in contrast to 8 R -DOX-AOS. Both enzymes oxidized 18:1 n -9 and 18:3 n -3 to α-ketols, but the catalysis of the 8 R - and 8 S -AOS domains differed. 8 R -DOX-AOS transformed 9 R -HPODE to epoxy alcohols, but 8 S -DOX-AOS converted 9 S -HPODE to an α-ketol (9-hydroxy-10-oxo-12 Z- octadecenoic acid) and epoxy alcohols in a ratio of ∼1:2. Whereas all fatty acid allene oxides described so far have a conjugated diene impinging on the epoxide, the allene oxides formed by 8-DOX-AOS are unconjugated.
