Product Specificity in an Entire Series of (ω-6 Z, ω-9 Z)-C13~C20-Dienoic Acids and -Dienols for Soybean Lipoxygenase

Abstract

Abstract Substrate specificity of soybean lipoxygenase-1 (EC 1.13.11.12) was studied using as synthetic substrate analogs an entire series of (ω-6 Z,ω-9 Z)-C13 ~ C20 (rdienoic acids and (ω-6 Z,ω-9 Z)- C12 ~ C20 (i-dienols. The relative activity of lipoxygenase-1 against linoleic acid (C18:2COOH) was the highest among the dienoic acids and that of (6Z.9Z)-pentadecadienol (C15:2OH) was the highest among the dienols. Soybean lipoxygenase-1 oxygenated almost at to- 6 position of the dienoic acids independently of the chain length. With the dienols as substrate, the position of oxygenation was much influenced by the chain length. Above all, C15:2OH was selectively oxygenated at ω-10 rather than at ω-6 . Kinetic analyses revealed that longer and more hydrophobic dienols had higher affinity but lower velocity of oxygenation reaction. But higher velocity was obtained when smaller Km value was observed for the dienoic acids. To clucidate stereospecificity of the oxygenation to C15:2OH, optically active authentic samples were prepared via biological asymmetric reduction with baker’s yeast. The ω- 6 oxygenation to C15:2OH was found to be (S)-specific (R/S = 26/74) as is that to C18:2COOH. whereas the ω-10 oxygenation showed low enantioselectivity (R/S - 60/40).