Premium
Intermediates and products formed during fatty acid α‐oxidation in cucumber ( Cucumis sativus )
Author(s) -
Andersen Borge Grethe I.,
Vogt Gjermund,
Nilsson Astrid
Publication year - 1999
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-999-0411-7
Subject(s) - palmitic acid , chemistry , formate , cucumis , beta oxidation , biochemistry , fatty acid , biology , catalysis , ecology
Fatty acid α‐oxidation is an essential metabolic pathway both in plants and in mammals which is still not completely understood. We previously described and purified an α‐oxidation enzyme in cucumber which has been used in the present investigation of the α‐oxidation reaction mechanism. Free fatty acids, and not the CoA thioesters, were found to undergo α‐oxidation in cucumber. 2‐Hydroxy‐ and 2‐oxopalmitic acids were identified as palmitic acid α‐oxidation intermediates by high‐performance liquid chromatography and gas chromatography—mass spectrometry analysis in cucumber subcellular 150,000× g max pellets obtained by differential centrifugation. Incubation of purified α‐oxidation enzyme with [1‐ 14 C]palmitic acid resulted in the formation of both the above‐described intermediates and the C n −1 product, pentadecanal, and 14 CO 2 . Besides 14 CO 2 , 14 C‐formate was identified as an α‐oxidation product from [1‐ 14 C]palmitic acid in cucumber subcellular fractions. Fe 2+ stimulated the 14 CO 2 and 14 C‐formate production, and the addition of ascorbate and 2‐oxoglutarate together with Fe 2+ resulted in optimal α‐oxidation activities, suggesting a dioxygenase reaction mechanism, as previously shown in mammals. NADPH and, to a lesser extent, NADH stimulated the total 14 C‐formate plus 14 CO 2 production but had only slight or no effects on 14 CO 2 production. H 2 O 2 showed concentration‐dependent inhibitory effects, while FAD had neither effect on 14 CO 2 nor 14 CO 2 plus 14 C‐formate production. The results in the present study demonstrate that an α‐oxidation enzyme in cucumber is capable of oxidizing palmitic acid via 2‐hydroxy‐ and 2‐oxopalmitic acid to produce pentadecanal and CO 2 . In contrast to the subcellular 150,000× g max fraction, the purified α‐oxidation enzyme could neither produce formate nor convert 14 C‐formate into 14 CO 2 , indicating two possible α‐oxidation routes in cucumber.