Acyl-CoA synthetase for long-chain fatty acids in rat small bowel and the influence of diets containing different compositions of fatty acids on intestinal lipid reesterifying enzyme activities

Abstract

1. 1. Kinetic studies of microsomal long chain acyl-CoA synthetase (acid:CoA ligase (AMP), EC 6.2.1.3) from rat jejunum using palmitic acid, oleic acid, and linoleic acid as substrates were performed. Kinetic studies were also done using whole jejunal mucosal homogenates. The enzyme assay employed was the hydroxamate-trapping method. 2. 2. Palmitic acid was found to mildly inhibit the enzyme reaction while oleic acid was shown to be a strong inhibitor. This inhibition by oleate could be partially overcome by the addition of large amounts of albumin. Plant lecithin, however, was found to be much more effective in reversing the inhibitory effects of oleic acid. 3. 3. Under ideal conditions for the enzyme assay specific activity of acyl-CoA synthetase for jejunal microsomes was 6–7 times greater than for jejunal homogenate. Recovery of total enzymatic activity in this subcellular fraction was about one-third of the amount calculated to be present in the whole jejunal homogenate. 4. 4. The effect of the long chain fatty acid composition of the diet on lipid reesterifying enzyme activities in the small bowel including palmitoyl-CoA synthetase, oleoyl-CoA synthetase and acyl-CoA :monoglyceride acyltransferase were also determined. No difference in specific or total small intestinal enzymatic activities were observed between two groups of rats, one on a diet for 3 weeks with a fatty acid composition of 13.8% saturated and 86.2% unsaturated and the other on a diet for a similar period containing 43.6% saturated and 56.4% unsaturated fatty acids. It was concluded that both saturated and unsaturated long chain fatty acids in the diet stimulate intestinal lipid reesterifying enzymatic activities equally well.