Long chain fatty acid:CoA ligase (EC 220.127.116.11.) was examined in human small intestinal mucosa using the hydroxamate-trapping method. With optimal assay requirements using palmitate as substrate a significant difference of specific activities could be detected in the total homogenate from duodenum, 40.9 +/- 11.6 nmol/min per mg protein versus upper jejunum, 51.9 +/- 13.7 (P less than 0.05). The enzyme activity of the microsomal fraction of upper jejunum was 101.8 +/- 44 nmol/min per mg protein. ATP, CoA, and Mg2+ were essential constituents of the reaction. A broad pH-optimum was observed between 6.75 and 7.75 with a maximum at a pH of 7.25. Whereas palmitate in the presence of albumin revealed a wide range of optimal concentration in supporting maximal enzyme activity, oleate was found to strongly inhibit the reaction. Where substrate specificity with both the total homogenate and the microsomal fraction was concerned, maximal reaction rates were obtained with palmitate for the long chain saturated fatty acids C12:0' C14:0' C16:0' and C18:0' and with oleate for the long chain unsaturated fatty acids C18:1 C18:2' and C18:3' respectively. The highest specific activity of the enzyme was localised in the microsomal fraction. The kinetic data and properties of the long chain fatty acid: CoA ligase from human intestine are discussed with respect to the intestinal enzyme from other species.
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