Studies on the Control of Fatty Acid Metabolism: II. THE INHIBITION OF FATTY ACID SYNTHESIS IN LACTOBACILLUS PLANTARUM BY EXOGENOUS FATTY ACID

Abstract

Abstract When Lactobacillus plantarum is cultured in a medium containing certain fatty acids, the synthesis of fatty acid by the organism is reduced. Of the fatty acids tested, oleic and cis-vaccenic acids exert the most pronounced inhibition, but significant inhibition is also produced by palmitoleic, lactobacillic, elaidic, linoleic, and eicosenoic acids. Linolenic acid, petroselenic acid, and the saturated fatty acids, myristic, palmitic, and stearic acids, have little or no such effect. The exogenous fatty acids are incorporated into the cellular lipids, thus altering the fatty acid composition. Experimental evidence suggests that the inhibition of fatty acid synthesis is a consequence of repression of enzyme synthesis. There is no evidence to suggest feedback inhibition of fatty acid synthesis. The activities of both acetyl-CoA carboxylase and fatty acid synthetase are considerably reduced. When L. plantarum is grown in the presence of oleic acid, the activity of the fatty acid synthetase drops below one-twentieth of its normal level. The level of the acetyl-CoA carboxylase also decreases, but to what precise extent remains undetermined because of the low activity of this enzyme in crude extracts. Several of the component enzymes of the fatty acid synthetase (the malonyl-CoA-ACP transacylase, the acetyl, malonyl-ACP condensing enzyme, the β-ketoacyl-ACP reductase, the β-hydroxybutyryl-ACP dehydrase, the β-hydroxyoctanoyl-ACP dehydrase, and the enoyl-ACP reductase) are reduced by 5 to 6 times when cells are grown in the presence of oleic acid—which suggests that the synthesis of these enzymes is under some form of coordinate control. The synthesis of unsaturated fatty acid is repressed more than the synthesis of saturated fatty acid, suggesting that the enzyme(s) required solely for the synthesis of unsaturated fatty acid is under a different level of control. The amount of the acyl carrier protein is also regulated since cells grown in the presence of oleic acid contain reduced levels of acyl carrier protein.