Incubation with sesame oil increases the mycelial dihomo-gamma-linolenic acid content of an arachidonic acid-producing fungus, Mortierella alpina, but decreases its arachidonic acid content [Shimizu, S., K. Akimoto, H. Kawashima, Y. Shinmen and H. Yamada (1989) J. Am. Oil Chem. Soc. 66, 237-241]. The factor causing these effects was isolated and identified to be (+)-sesamin. The results obtained in experiments with both a cell-free extract of the fungus and with rat liver microsomes demonstrated that (+)-sesamin specifically inhibits delta 5 desaturase at low concentrations, but does not inhibit delta 6, delta 9 and delta 12 desaturases. Kinetic analysis showed that (+)-sesamin is a noncompetitive inhibitor (Ki for rat liver delta 5 desaturase, 155 microM). (+)-Sesamolin, (+)-sesaminol and (+)-episesamin also inhibited only delta 5 desaturases of the fungus and liver. These results demonstrate that (+)-sesamin and related lignan compounds present in sesame seeds or its oil are specific inhibitors of delta 5 desaturase in polyunsaturated fatty acid biosynthesis in both microorganisms and animals.
Various microorganisms were screened for high arachidonic acid productivity. An isolated fungus, strain 1S-5, identified as Mortierella elongata Linnemann, was found to show the highest productivity. Using this fungus, the cultural conditions for high intracellular production of arachidonic acid were investigated. The production of arachidonic acid reached 0.99mg/ml (22mg/g dry cells) when the fungus was grown in a medium containing 10% glucose, 0.5% Polypepton and 0.3% yeast extract, pH 6.0, for 4 days at 24°C with shaking. The arachidonic acid could be isolated as the methyl ester from mycelia with a good recovery. Arachidonic acid (eicosa-5,8,ll,14-tetra
Mycelia of arachidonic acid‐producing fungi belonging to the genusMortierella were found to be rich sources of 5,8,11,14,17‐cis‐eicosapentaenoic acid (EPA). Production of EPA by these fungi was observed only when they were grown at low temperature (6–16 C). EPA comprised 5–20% of the total extractable mycelial fatty acids in most strains tested. No significant accumulation of EPA was observed on incubation at high temperature (20–28 C), at which the other major mycelial C‐20 fatty acid, arachidonic acid, was still efficiently produced. In a study on the optimization of the culture conditions for EPA production by a selected fungiM. alpina 20–17, a medium containing glucose and yeast extract as major carbon and nitrogen sources, respectively, was found to be suitable. Periodic feeding of glucose during growth of the fungus and cultivation at high temperature (20 C) during the early growth phase followed by temperature shift to 12 C were found to be effective at increasing mycelial yield and reducing cultural period, respectively. Under the optimal culture conditions, the EPA production reached 0.49 mg/ml of culture broth (29 mg/g dry mycelia). This value accounted for 13.5% of the total fatty acids in the extracted lipids. Other major fatty acids in the lipids were palmitic acid (6.0%, by weight), stearic acid (5.3), oleic acid (6.2), linoleic acid (3.0), γ‐linolenic acid (3.5) and arachidonic acid (60.0).
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