Chain elongation of fatty acids in rat small intestine: subcellular localization and effects of clofibrate and partially hydrogenated fish oil.

Clofibrate treatment was found to increase by a factor of two the activity of malonyl-CoA-dependent palmitic acid chain elongation in crude 'microsomal' fractions isolated from rat small intestine. A slight stimulation was indicated also after feeding a high fat diet containing partially hydrogenated fish oil (PHFO). This effect was, however, not statistically significant. Subcellular localization of this chain elongation activity was studied by Nycodenz gradient centrifugation. Chain elongation of palmitic acid was observed only in fractions containing high esterase activity, suggesting a microsomal localization. Similar distributions were seen after feeding the peroxisomal proliferators clofibrate and PHFO. Chain-shortening activity was found in the fractions containing high catalase activity, confirming our earlier studies suggesting a peroxisomal localization of this activity also in rat small intestine.