耐冷菌Pseudomonas Sp. Strain E-3における不飽和脂肪酸の合成

Biosynthetic pathway of unsaturated fatty acids in a psychrotrophic bacterium, Pseudomonas sp. Strain E-3, was examined． The results obtained by gas-chromatography-mass-spectrometry demonstrated that the main unsaturated fatty acids in this bacterium are △9-C 16：1 and △11-C 18：1.On the other hand，fatty acid synthetase was partially purified，which produced saturated and unsaturated fatty acids（anaerobic pathway）．This is first report which demonstrate the co-existence of two pathways for the biosynthesis of unsaturated fatty acids in one organism.3-Decynoyl-NAC，specific inhibitor of the anaerobic pathway，completely inhibited the synthesis of unsaturated fatty acid by partially purified fatty acid synthetase．However，the inhibitor did not blocked the unsaturated fatty acid synthesis in whole cells and reconstituted system which contained fatty acid synthetase and the membrane fraction．High concentration of 3-decynoyl-NAC completely inhibited the cell growth，but the growth inhibition was completely restored by addition of △9-C18：1and partly recovered by addition of C16：0 to the growth medium. Thus，the aerobic pathway can synthesize unsaturated fatty acids to sustain cell growth under the condition in which the anaerobic pathway was blocked．Pseudomonas sp. Strain E-3 grew in the medium which contained a fatty acid or hydrocarbon as the sole carbon source． Fatty acid composition of phospholipids and growth curve were affected by the carbon source．The added fatty acid and its desaturation product were increased in phospholipids．Saturated and unsaturated odd-chain fatty acids appeared in phospholipids of the cells grown on C 11：0 or C 15：0, though odd-chain fatty acid was not synthesized de novo. The in vivodesaturase activity was increased when the cells were grown on the carbon source which was the enzyme substrate， whereas the activity was lowered whenthe carbon source was unsaturated fatty acid．Composition of de novo synthesized fatty acids was altered to save the synthesis of the supplemented one．Therefore，this bacterium utilizes efficiently exogenous long chain fatty acid for the membrane lipids synthesis with and without modification（desaturation and elongation）. Fatty acidmetabolism was regulated in accordance with the cellular economy