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

Oxygenation of linoleic acid by Aspergillus terreus was studied with LC-MS/MS. 9(R)-Hydroperoxy-10(E), 12(Z)-octadecadienoic acid (9R-HpODE) was identified along with 10(R)-hydroxy-8(E),I 2(Z)-octadecadienoic acid and variable amounts of 8(R)-hydroxy-9(Z),12(Z)-octadecadienoic acid. 9R-HpODE was formed from [11S-H-2]18:2n-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 (alpha-ketol) and 13-hydroxy-10-oxo-11 (E)-octadecenoic acid (gamma-ketol), likely formed by spontaneous hydrolysis of an unstable allene oxide, 9(R),10-epoxy-10,12(Z)-octadecadienoic acid. alpha-Linolenic acid and 20:2n - 6 were oxidized to hydroperoxy fatty acids at C-9 and C-11, respectively, but alpha- and gamma-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 10R-dioxygenases of aspergilli. Our results demonstrate that linoleate 9R-dioxygenase linked to allene oxide synthase activities can be expressed in fungi. (C) 2009 Elsevier Inc. All rights reserved