Linoleate 9 R-dioxygenase and allene oxide synthase activities of Aspergillus terreus

Abstract

Oxygenation of linoleic acid by Aspergillus terreus was studied with LC–MS/MS. 9( R) -Hydroperoxy-10( E),12( Z)-octadecadienoic acid (9 R-HpODE) was identified along with 10( R)-hydroxy-8( E),12( Z)-octadecadienoic acid and variable amounts of 8( R)-hydroxy-9( Z),12( Z)-octadecadienoic acid. 9 R-HpODE was formed from [11 S- 2H]18:2 n − 6 with loss of the deuterium label, suggesting antarafacial hydrogen abstraction and oxygenation. Two polar metabolites were identified as 9-hydroxy-10-oxo-12( Z)-octadecenoic acid (α-ketol) and 13-hydroxy-10-oxo-11( E)-octadecenoic acid (γ-ketol), likely formed by spontaneous hydrolysis of an unstable allene oxide, 9( R),10-epoxy-10,12( Z)-octadecadienoic acid. α-Linolenic acid and 20:2 n − 6 were oxidized to hydroperoxy fatty acids at C-9 and C-11, respectively, but α- and γ-ketols of these fatty acids could not be detected. The genome of A. terreus lacks lipoxygenases, but contains genes homologous to 5,8-linoleate diol synthases and linoleate 10 R-dioxygenases of aspergilli. Our results demonstrate that linoleate 9 R-dioxygenase linked to allene oxide synthase activities can be expressed in fungi.