出版社：American Society for Biochemistry and Molecular Biology
摘要：manganese lipoxygenase (Mn-LO) oxygenates 18:3n-3 and 18:2n-6 to bis -allylic 11 S -hydroperoxy fatty acids, which are converted to 13 R -hydroperoxy fatty acids. Other unsaturated C16-C22 fatty acids, except 17:3n-3, are poor substrates, possibly because of ineffective enzyme activation (MnII→MnIII) by the produced hydroperoxides. Our aim was to determine whether unsaturated C16-C22 fatty acids were oxidized by MnIII-LO. MnIII-LO oxidized C16, C19, C20, and C22 n-3 and n-6 fatty acids. The carbon chain length influenced the position of hydrogen ion (n-8, n-5) and oxygen insertion at the terminal or the penultimate 1 Z ,4 Z -pentadienes. Dilinoleoyl-glycerophosphatidylcholine was oxidized by Mn-LO, in agreement with a “tail-first” model. 16:3n-3 was oxidized at the bis -allylic n-5 carbon and at positions n-3, n-7, and n-6. Long fatty acids, 19:3n-3, 20:3n-3, 20:4n-6, 22:5n-3, and 22:5n-6, were oxidized mainly at the n-6 and the bis -allylic n-8 positions (in ratios of ∼3:2). The bis -allylic hydroperoxides accumulated with one exception, 13 - hydroperoxyeicosatetraenoic acid (13-HPETE). MnIII-LO oxidized 20:4n-6 to 15 R -HPETE (∼60%) and 13-HPETE (∼37%) and converted 13-HPETE to 15 R -HPETE. MnIII-LO G316A oxygenated mainly 16:3n-3 at positions n-7 and n-6, 19:3n-3 at n-10, n-8, and n-6, and 20:3n-3 at n-10 and n-8. We conclude that Mn-LO likely binds fatty acids tail-first and oxygenates many C16, C18, C20, and C22 fatty acids to significant amounts of bis -allylic hydroperoxides.
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