Enzymic oxidation of linolenic acid to 1,Z-5-octadien-3-ol, Z-2,Z-5-octadien-1-ol and 10-oxo-E-8-decenoic acid by a protein fraction from mushrooms (Psalliota bispora).

The pathway for the oxidative cleavage of linolenic acid was investigated using a protein fraction from mushrooms (Psalliota bispora) as the enzyme source. Incubation of the protein fraction with linolenic acid resulted in 1,Z-5-octadien-3(R)-ol and Z-2,Z-5-octadien-1-ol (in a 3∶2 ratio) and 10-oxo-E-8-decenoic acid (10-ODA). Experiments with molecular oxygen-18 indicated that the oxygen in the hydroxy group of both octadienols originates from the gaseous phase and not from water. The protein fraction was incubated with the individual 9-, 10-, 12-, 13-, 15- and 16-hydroperoxide isomers of linolenic acid. Only the 10-hydroperoxy-E-8,Z-12,Z-15-octadecatrienoic acid (10-HPOT) served as substrate, and was cleaved into the two octadienols and the 10-ODA. This result suggests that in the oxidation of linolenic acid by the mushroom fraction the 10-HPOT is an intermediate cleaved by a hydroperoxide lyase into the octadienols and the 10-ODA. Model experiments in which the methyl esters of both 10-hydroperoxy-E-8,Z-12-octadecadienoic acid (10-HPOD) and 10-HPOT were treated with the Lewis acid BF3 yielded only various C9 compounds. It was therefore concluded that the reactions of the mushroom hydroperoxide lyase cannot be explained by the heterolytic rearrangement mechanism, which was proposed for the corresponding plant enzyme. β-Scission of the 10-HPOD and the 10-HPOT explains the reactions of the mushroom hydroperoxide lyase and is discussed in detail.