Abstract
beta-Oxidation of unsaturated fatty acids was studied with isolated solubilized or nonsolubilized peroxisomes or with perfused liver isolated from rats treated with clofibrate. gamma-Linolenic acid gave the higher rate of beta-oxidation, while arachidonic acid gave the slower rate of beta-oxidation. Other polyunsaturated fatty acids (including docosahexaenoic acid) were oxidized at rates which were similar to, or higher than, that observed with oleic acid. Experiments with 1-14C-labeled polyunsaturated fatty acids demonstrated that these are chain-shortened when incubated with nonsolubilized peroxisomes. Spectrophotometric investigation of solubilized peroxisomal incubations showed that 2,4-dienoyl-CoA esters accumulated during peroxisomal beta-oxidation of fatty acids possessing double bond(s) at even-numbered carbon atoms. beta-Oxidation of [1-14C]docosahexaenoic acid by isolated peroxisomes was markedly stimulated by added NADPH or isocitrate. This fatty acid also failed to cause acyl-CoA-dependent NADH generation with conditions of assay which facilitate this using other acyl-CoA esters. These findings suggest that 2,4-dienoyl-CoA reductase participation is essential during peroxisomal beta-oxidation if chain shortening is to proceed beyond a delta 4 double bond. Evidence obtained using arachidionoyl-CoA, [1-14C]arachidonic acid, and [5,6,8,9,11,12,14,15-3H]arachidonic acid suggests that peroxisomal beta-oxidation also can proceed beyond a double bond positioned at an odd-numbered carbon atom. Experiments with isolated perfused livers showed that polyunsaturated fatty acids also in the intact liver are substrates for peroxisomal beta-oxidation, as judged by increased levels of the catalase-H2O2 complex on infusion of polyunsaturated fatty acids.
Highlights
From the $Department of Biochemistry, NorwegianCollege of Veterinary Medicine, Oslo, Norway, and $Department of Medicd Biochemistry, University of Oulu, Oulu, Finland &Oxidation of unsaturated fatty acids was studied high fat diets rich in such fatty acids [3]. It has been with isolated solubilizedor nonsolubilizedperoxisomes suggested that impaired peroxisomal @-oxidationis the cause or with perfused liver isolated from rats treated with of accumulation of very long chain saturated fatty acids in clofibrate. y-Linolenic acid gave the higher rate of 0- individuals suffering from X-linked adrenoleucodystrophy oxidation, while arachidonic acid gave theslower rate of @-oxidation.Other polyunsaturated fatty acids were oxidized at rates which were similar to, or higher than, that observed with oleic acid
@-Oxidationof Various Polyunsaturated Fatty Acids by Nonsolubilized Peroxisomes-The results presented in Fig. 1show that of the various fatty acids examined the rate of oxidation of [l-'4C]linolenic acid was by far fastest.[l-'4C]Linoleic acid was, oxidized at a somewhat slower rate, the other fatty acids
Most of these unsaturated fatty acids are oxidized at rates which are similar to, or higher than, the rate observed with oleic acid (Figs. 1 and 2)
Summary
"Means which are significantly different ( p < 0.05)from that obtained with oleic acid. A modified t test was used to test the significance of differences between means [39]. The final concentration of bovine serum albumin was 2 mg/ml. The incubation mixture contained 5 mM ATP and 5 mMMgC1, to facilitate activation of the fatty acid by the peroxisomal acyl-CoAsynthetase (EC 6.2.1.3) [20].Incubations were carried out at 37 "C in a shaking water bath. It was always ensured that a linear relationship existed between amount of fatty acid oxidized and the amount of peroxisomal protein present in the incubations. In spectrophotometric work peroxisomal fractions isolated in Nycodenz gradients were used, and rates of &oxidation were measured with acyl-CoA esters as substrates.
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