Incomplete palmitate oxidation in cell-free systems of rat and human muscles

The palmitate oxidation capacity was determined in whole homogenates, postnuclear fractions and mitochondrial fractions of various rat and human muscles and in rat liver, kidney, brain and lung. The oxidation rate (production of 14CO2 and 14C-labeled acid-soluble intermediates) was [1-14C]palmitate greater than [U-14C]palmitate greater than [16-14C]palmitate in all cell-free systems. Oxidation rates were highest in rat heart and liver, intermediate in kidney, diaphragm and m. quadriceps, and low in brain and lung. The capacity of human heart was much lower than that of rat heart and about twice that of human skeletal muscles. Omission of L-carnitine and addition of malonyl-CoA, KCN or antimycin A decreased the oxidation rates in whole homogenates and mitochondrial fractions. Antimycin or KCN increased and malonyl-CoA decreased the ratio of the oxidation rates with [1-14C]- and [16-14C]palmitate. The carnitine concentration had no significant effect on the ratio. 14C-labeled dodecanoic and tetradecanoic acids were identified in homogenates and mitochondrial fractions of m. quadriceps and liver of rat as acid-insoluble intermediates of [16-14C]palmitate oxidation in the presence and absence of antimycin A. Their amounts recovered can account for the differences in oxidation rates found with [1-14C]- and [16-14C]palmitate. The incomplete palmitate oxidation in cell-free systems appears to be mainly caused by an inadequate mitochondrial degradation of peroxisomal oxidation products.     

Peroxisomal-mitochondrial oxidation in a rodent model of obesity-associated insulin resistance

Peroxisomal oxidation yields metabolites that are more efficiently utilized by mitochondria. This is of potential clinical importance because reduced fatty acid oxidation is suspected to promote excess lipid accumulation in obesity-associated insulin resistance. Our purpose was to assess peroxisomal contributions to mitochondrial oxidation in mixed gastrocnemius (MG), liver, and left ventricle (LV) homogenates from lean and fatty (fa/fa) Zucker rats. Results indicate that complete mitochondrial oxidation (CO(2) production) using various lipid substrates was increased approximately twofold in MG, unaltered in LV, and diminished approximately 50% in liver of fa/fa rats. In isolated mitochondria, malonyl-CoA inhibited CO(2) production from palmitate 78%, whereas adding isolated peroxisomes reduced inhibition to 21%. These data demonstrate that peroxisomal products may enter mitochondria independently of CPT I, thus providing a route to maintain lipid disposal under conditions where malonyl-CoA levels are elevated, such as in insulin-resistant tissues. Peroxisomal metabolism of lignoceric acid in fa/fa rats was elevated in both liver and MG (LV unaltered), but peroxisomal product distribution varied. A threefold elevation in incomplete oxidation was solely responsible for increased hepatic peroxisomal oxidation (CO(2) unaltered). Alternatively, only CO(2) was detected in MG, indicating that peroxisomal products were exclusively partitioned to mitochondria for complete lipid disposal. These data suggest tissue-specific destinations for peroxisome-derived products and emphasize a potential role for peroxisomes in skeletal muscle lipid metabolism in the obese, insulin-resistant state.     

Peroxisomal fatty acid oxidation in rat and human tissues. Effect of nutritional state, clofibrate treatment and postnatal development in the rat

Oxidation of palmitate 14C-labeled in different positions was assayed in the absence and presence of antimycin and rotenone in homogenates of various rat and human tissues to determine total and peroxisomal oxidation and acetyl group production. Total and antimycin-insensitive palmitate oxidation rates were higher in rat heart, liver and quadriceps muscle than in the corresponding human tissues. The proportion of antimycin-insensitive oxidation of [1-14C]palmitate was 17-35% in tissues of starved rats and in human muscles and fibroblasts, but peroxisomal production of acetyl groups amounted only to 5-11% of that by mitochondria. The mean number of peroxisomal beta-oxidation cycles was 1.5-2.5 per palmitate molecule. The nutritional state markedly influenced the total oxidation rate and the antimycin-insensitive proportion in rat liver. Clofibrate feeding increased total and antimycin-insensitive oxidation rates in liver, heart and kidney, but not in quadriceps muscle. Total oxidation capacity was maximal in rat liver at weaning, and in rat heart at an age of 70 days. Antimycin-insensitive oxidation rates increased in rat liver and heart at postnatal development up to weaning. A marked proportion of lignocerate oxidation was antimycin-sensitive in rat tissues.     

Glyoxylate cycle in the rat liver: effect of vitamin D3 treatment

Evidence for the glyoxylate cycle in the mammalian rat liver was sought. Activity of two unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase, was found in rat liver homogenates. Vitamin D3 treatment of rachitic animals produced a five- and fourfold increase, respectively, in the activity of these enzymes. Vitamin D3 also increased the peroxisomal fatty acid oxidation and the accumulation of glycogen in liver slices in the presence of palmitate. These data suggest that the mammalian rat liver can convert fatty acid carbon to carbohydrate carbon directly.     

Acyl-CoA oxidase activity and peroxisomal fatty acid oxidation in rat tissues

Acyl-CoA oxidase, the first enzyme of the peroxisomal β-oxidation, was proved to be rate-limiting for this process in homogenates of rat liver, kidney, adrenal gland, heart and skeletal muscle. Acyl-CoA oxidase activity, based on H₂O₂-dependent leuko-dichlorofluorescein oxidation in tissue extract, was compared with radiochemically assayed peroxisomal β-oxidation rates. Dichlorofluorescein production was a valid measure of peroxisomal fatty acid oxidation only in liver and kidney, but not in adrenal gland, heart or skeletal muscle. Production of ¹⁴C-labeled acid-soluble products from 1-¹⁴C-labeled fatty acids in the presence of antimycin-rotenone appears to be a more accurate and sensitive estimate of peroxisomal β-oxidation than the acyl-CoA oxidase activity on base of H₂O₂ production. Chain-length specificity of acyl-CoA oxidase changed with the acyl-CoA concentrations used. Below 80 μM, palmitoyl-CoA showed the highest activity of the measured substrates in rat liver extract. No indications were obtained for the presence in rat liver of more forms of acyl-CoA oxidase with different chain-length specificity.     

Inhibition of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid oxidation and of bile acid secretion in rat liver by fatty acids

In isolated rat hepatocytes, fatty acids inhibited the side chain oxidation, but not the uptake, of exogenously added 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid (THCA). THCA did not inhibit fatty acid oxidation. In liver homogenates, fatty acids inhibited THCA activation to its CoA ester (THC-CoA) and THCA oxidation. THCA did not influence fatty acid activation or oxidation. Comparison of the THC-CoA concentrations present in the incubation mixtures during THCA oxidation, with substrate concentration curves determined for THC-CoA oxidation, indicated that the inhibition of THCA oxidation by fatty acids was at least partly exerted at the activation step. The inhibition of THCA activation by fatty acids was noncompetitive. Palmitoyl-CoA at concentrations found in the incubation mixtures during THCA oxidation in the presence of palmitate inhibited THC-CoA oxidation, but not sufficiently to fully explain the fatty acid-induced inhibition of THCA oxidation. The inhibition of THC-CoA oxidation by palmitoyl-CoA did not seem to be competitive. Acyl-CoA oxidase, the first enzyme of peroxisomal beta-oxidation (which catalyzes the side chain oxidation of THCA), was enhanced 15-fold in liver homogenates from clofibrate-treated rats when palmitoyl-CoA was the substrate, but the oxidase activity remained unaltered when THC-CoA was the substrate. In the perfused liver, oleate, infused after a wash-out period of 60 min, markedly inhibited bile acid secretion. The results 1) suggest that fatty acids inhibit THCA metabolism both at the activation step and at the peroxisomal beta-oxidation sequence and that separate enzymes may be involved in both the activation and peroxisomal beta-oxidation of fatty acids and THCA and 2) raise the question whether fatty acids might (indirectly?) affect overall bile acid synthesis via their inhibitory effect on THCA metabolism.     

Peroxisomal fatty acid oxidation is a substantial source of the acetyl moiety of malonyl-CoA in rat heart

Little is known about the sources of acetyl-CoA used for the synthesis of malonyl-CoA, a key regulator of mitochondrial fatty acid oxidation in the heart. In perfused rat hearts, we previously showed that malonyl-CoA is labeled from both carbohydrates and fatty acids. This study was aimed at assessing the mechanisms of incorporation of fatty acid carbons into malonyl-CoA. Rat hearts were perfused with glucose, lactate, pyruvate, and a fatty acid (palmitate, oleate or docosanoate). In each experiment, substrates were (13)C-labeled to yield singly or/and doubly labeled acetyl-CoA. The mass isotopomer distribution of malonyl-CoA was compared with that of the acetyl moiety of citrate, which reflects mitochondrial acetyl-CoA. In the presence of labeled glucose or lactate/pyruvate, the (13)C labeling of malonyl-CoA was up to 2-fold lower than that of mitochondrial acetyl-CoA. However, in the presence of a fatty acid labeled in its first acetyl moiety, the (13)C labeling of malonyl-CoA was up to 10-fold higher than that of mitochondrial acetyl-CoA. The labeling of malonyl-CoA and of the acetyl moiety of citrate is compatible with peroxisomal beta-oxidation forming C(12) and C(14) acyl-CoAs and contributing >50% of the fatty acid-derived acetyl groups that end up in malonyl-CoA. This fraction increases with the fatty acid chain length. By supplying acetyl-CoA for malonyl-CoA synthesis, peroxisomal beta-oxidation may participate in the control of mitochondrial fatty acid oxidation in the heart. In addition, this pathway may supply some acyl groups used in protein acylation, which is increasingly recognized as an important regulatory mechanism for many biochemical processes.     

An accurate and sensitive assay of [14C]octanoate oxidation and its application on tissue homogenates and fibroblasts

A procedure was developed to assay [14C]octanoate oxidation from the production of both 14CO2 and 14C-labeled acid-soluble products. Octanoic acid and its CoA and carnitine esters were eliminated from the acid-soluble products by alkaline hydrolysis of the esters and acidification and binding of the acid to Lipidex 1000. The method was evaluated with homogenates of various rat tissues and human muscles and with human fibroblasts. 14CO2 production was variable and comprised less than 3% of the total oxidation products with homogenates and 26 +/- 19% with fibroblasts. As compared to palmitate, oxidation rates of octanoate were higher in rat liver and heart homogenates, of the same magnitude in muscle homogenates, but lower in fibroblasts. The proportion of antimycin-insensitive oxidation was much lower with octanoate than with palmitate. Using the assay a case of medium-chain acyl-CoA dehydrogenase deficiency could be indicated.     

14CO2 production is no adequate measure of [14C]fatty acid oxidation

Palmitate oxidation was comparatively assayed in various cell-free and cellular systems by 14CO2 production and by the sum of 14CO2 and 14C-labeled acid-soluble products. The 14CO2 production rate was dependent on incubation time and amount of tissue in contrast to the total oxidation rate. The 14CO2 contribution to the oxidation rate of [1-14C]palmitate varied with homogenates from 1% with rat liver to 28% with rat kidney and amounted to only 2-4% with human muscles. With cellular systems the 14CO2 contribution varied between 20% in human fibroblasts and 70% in rat muscles and myocytes. Addition of cofactors increased the oxidation rate, but decreased the 14CO2 contribution. Various conditions appeared also to influence to a different extent the 14CO2 production and the total oxidation rate with rat tissue homogenates and with rat muscle mitochondria. Incorporation of radioactivity from [1-14C]palmitate into protein was not detectable in cell-free systems and only 2-3% of the sum of 14CO2 and 14C-labeled acid-soluble products in cellular systems. Assay of 14CO2 and 14C-labeled acid-soluble products is a much more accurate and sensitive estimation of fatty acid oxidation than assay of only 14CO2.     

The effect of di(ethylhexyl)phthalate on fatty acid oxidation and carnitine palmitoyltransferase in various rat tissues

Male rats were fed a diet with or without 2% di(2-ethylhexyl)phthalate (DEHP) for 12 days. Total and peroxisomal oxidation rates of palmitic and arachidonic acid were increased in homogenates of liver and kidney after DEHP administration. The relative peroxisomal contribution to the total oxidation was only higher in liver. The activities of acyl-CoA oxidase and carnitine palmitoyltransferase were also higher in both tissues. Immunoblots showed that the increase of fatty acid oxidation was associated with a higher concentration of enzymes of peroxisomal and mitochondrial beta-oxidation. DEHP did not change total and peroxisomal fatty acid oxidation and activity of carnitine palmitoyltransferase of homogenates of heart and skeletal muscle. The cause for the tissue-specific response is discussed.     

The action of vasopressin and calcium on palmitate metabolism in hepatocytes and isolated mitochondria from rat liver

Vasopressin inhibits fatty acid oxidation and stimulates fatty acid esterification, glycogenolysis, and lactate production in hepatocytes from fed rats. In cells from fasted rats, the effect of the hormone on palmitate oxidation was absent, while gluconeogenesis was stimulated. The inhibitory action of vasopressin on palmitate oxidation was not due to the increased lactate production. Neither was it correlated to glycogen content or stimulation of glycogenolysis, which were restored earlier than the vasopressin effect on palmitate oxidation when previously fasted rats were refed a carbohydrate diet. The level of malonyl-CoA was moderately increased by vasopressin. Isolated mitochondria from rat liver were incubated in the presence of [U-14C]palmitate, ATP, CoA carnitine, glycerophosphate, ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid, and varying amounts of calcium. The oxidation of palmitate was inhibited when the concentration of free calcium was increased from about 0.1 to 10 microM. Simultaneously, palmitate esterification was stimulated. This effect of calcium was observed also with mitochondria from fasted rats and with octanoate as well as palmitate as the substrate. Carnitine acylation was not affected by calcium. The possibility that the observed effects of calcium on mitochondrial fatty acid utilization is part of the mechanism of action of vasopressin on hepatocyte fatty acid metabolism is discussed.     

Evidence of a malonyl-CoA-insensitive carnitine palmitoyltransferase I activity in red skeletal muscle

Carnitine palmitoyltransferase I (CPT I), which is expressed as two distinct isoforms in liver (alpha) and muscle (beta), catalyzes the rate-limiting step in the transport of fatty acid into the mitochondria. Malonyl-CoA, a potent inhibitor of CPT I, is considered a key regulator of fatty acid oxidation in both tissues. Still unanswered is how muscle beta-oxidation proceeds despite malonyl-CoA concentrations that exceed the IC(50) for CPT Ibeta. We evaluated malonyl-CoA-suppressible [(14)C]palmitate oxidation and CPT I activity in homogenates of red (RG) and white (WG) gastrocnemius, soleus (SOL), and extensor digitorum longus (EDL) muscles. Adding 10 microM malonyl-CoA inhibited palmitate oxidation by 29, 39, 60, and 89% in RG, SOL, EDL, and WG, respectively. Thus malonyl-CoA resistance, which correlated strongly (0.678) with absolute oxidation rates (RG > SOL > EDL > WG), was greater in red than in white muscles. Similarly, malonyl-CoA-resistant palmitate oxidation and CPT I activity were greater in mitochondria from RG compared with WG. Ribonuclease protection assays were performed to evaluate whether our data might be explained by differential expression of CPT I splice variants. We detected the presence of two CPT Ibeta splice variants that were more abundant in red compared with white muscle, but the relative expression of the two mRNA species was unrelated to malonyl-CoA resistance. These results provide evidence of a malonyl-CoA-insensitive CPT I activity in red muscle, suggesting fiber type-specific expression of distinct CPT I isoforms and/or posttranslational modulations that have yet to be elucidated.     

Immunochemical analysis of the peroxisomal beta-oxidation enzymes in rat and human heart and skeletal muscle and in skeletal muscle of Zellweger patients

Immunoblot analyses with antibodies against the peroxisomal beta-oxidation enzymes from rat liver showed the presence of these enzymes in rat and human liver and kidney and rat adrenal gland. The bifunctional protein could not be detected in muscle tissues or cultured muscle cells. Acyl-CoA oxidase was detected in rat heart and cultured human muscle cells. 3-Ketoacyl-CoA thiolase was also detected in human and rat heart and skeletal muscle; however, this enzyme was not detectable in skeletal muscle of Zellweger patients, in agreement with the absence of peroxisomal fatty acid oxidation.     

Mitochondrial and peroxisomal fatty acid oxidation in liver homogenates and isolated hepatocytes from control and clofibrate-treated rats.

Mitochondrial and peroxisomal fatty acid oxidation were compared in whole liver homogenates. Oxidation of 0.2 mM palmitoyl-CoA or oleate by mitochondria increased rapidly with increasing molar substrate:albumin ratios and became saturated at ratios below 3, while peroxisomal oxidation increased more slowly and continued to rise to reach maximal activity in the absence of albumin. Under the latter condition mitochondrial oxidation was severely depressed. In homogenates from normal liver peroxisomal oxidation was lower than mitochondrial oxidation at all ratios tested except when albumin was absent. In contrast with mitochondrial oxidation, peroxisomal oxidation did not produce ketones, was cyanide-insensitive, was not dependent on carnitine, and was not inhibited by (+)-octanoylcarnitine, malonyl-CoA and 4-pentenoate. Mitochondrial oxidation was inhibited by CoASH concentrations that were optimal for peroxisomal oxidation. In the presence of albumin, peroxisomal oxidation was stimulated by Triton X-100 but unaffected by freeze-thawing; both treatments suppressed mitochondrial oxidation. Clofibrate treatment increased mitochondrial and peroxisomal oxidation 2- and 6- to 8-fold, respectively. Peroxisomal oxidation remained unchanged in starvation and diabetes. Fatty acid oxidation was severely depressed by cyanide and (+)-octanoylcarnitine in hepatocytes from normal rats. Hepatocytes from clofibrate-treated rats, which displayed a 3- to 4-fold increase in fatty acid oxidation, were less inhibited by (+)-octanoylcarnitine. Hydrogen peroxide production was severalfold higher in hepatocytes from treated animals oxidizing fatty acids than in control hepatocytes. Assuming that all H2O2 produced during fatty acid oxidation was due to peroxisomal oxidation, it was calculated that the contribution of the peroxisomes to fatty acid oxidation was less than 10% both in cells from control and clofibrate-treated animals.     

Leptin activates cardiac fatty acid oxidation independent of changes in the AMP-activated protein kinase-acetyl-CoA carboxylase-malonyl-CoA axis

Leptin regulates fatty acid metabolism in liver, skeletal muscle, and pancreas by partitioning fatty acids into oxidation rather than triacylglycerol (TG) storage. Although leptin receptors are present in the heart, it is not known whether leptin also regulates cardiac fatty acid metabolism. To determine whether leptin directly regulates cardiac fatty acid metabolism, isolated working rat hearts were perfused with 0.8 mm [9,10-(3)H]palmitate and 5 mm [1-(14)C]glucose to measure palmitate and glucose oxidation rates. Leptin (60 ng/ml) significantly increased palmitate oxidation rates 60% above control hearts (p < 0.05) and decreased TG content by 33% (p < 0.05) over the 60-min perfusion period. In contrast, there was no difference in glucose oxidation rates between leptin-treated and control hearts. Although leptin did not affect cardiac work, oxygen consumption increased by 30% (p < 0.05) and cardiac efficiency was decreased by 42% (p < 0.05). AMP-activated protein kinase (AMPK) plays a major role in the regulation of cardiac fatty acid oxidation by inhibiting acetyl-CoA carboxylase (ACC) and reducing malonyl-CoA levels. Leptin has also been shown to increase fatty acid oxidation in skeletal muscle through the activation of AMPK. However, we demonstrate that leptin had no significant effect on AMPK activity, AMPK phosphorylation state, ACC activity, or malonyl-CoA levels. AMPK activity and its phosphorylation state were also unaffected after 5 and 10 min of perfusion in the presence of leptin. The addition of insulin (100 microunits/ml) to the perfusate reduced the ability of leptin to increase fatty acid oxidation and decrease cardiac TG content. These data demonstrate for the first time that leptin activates fatty acid oxidation and decreases TG content in the heart. We also show that the effects of leptin in the heart are independent of changes in the AMPK-ACC-malonyl-CoA axis.     

Metabolism and short-term metabolic effects of conjugated linoleic acids in rat hepatocytes

Metabolic fate and short-term effects of a 1:1 mixture of cis-9,trans-11 and trans-10,cis-12-conjugated linoleic acids (CLA), compared to linoleic acid (LA), on lipid metabolism was investigated in rat liver. In isolated mitochondria CLA-CoA were poorer substrates than LA-CoA for carnitine palmitoyltransferase-I (CPT-I) activity. However, in digitonin-permeabilized hepatocytes, where interactions among different metabolic pathways can be simultaneously investigated, CLA induced a remarkable stimulatory effect on CPT-I activity. This stimulation can be ascribed to a reduced malonyl-CoA level in turn due to inhibition of acetyl-CoA carboxylase (ACC) activity. The ACC/malonyl-CoA/CPT-I system can therefore represent a coordinate control by which CLA may exert effects on the partitioning of fatty acids between esterification and oxidation. Moreover, the rate of oxidation to CO2 and ketone bodies was significantly higher from CLA; peroxisomes rather than mitochondria were responsible for this difference. Interestingly, peroxisomal acyl-CoA oxidase (AOX) activity strongly increased by CLA-CoA compared to LA-CoA. CLA, metabolized by hepatocytes at a higher rate than LA, were poorer substrates for cellular and VLDL-triacylglycerol (TAG) synthesis. Overall, our results suggest that increased fatty acid oxidation with consequent decreased fatty acid availability for TAG synthesis is a potential mechanism by which CLA reduce TAG level in rat liver.     

Oxidation of oleic and elaidic acids in rat and human heart homogenates

Parallel incubations with uniformly 14C-labeled oleic and elaidic acids were conducted to compare oxidation rates in tissue homogenates prepared from rat and human hearts. Radioactivity in 14CO2 and 14C-labeled chain-shortened acid-soluble products was used to measure the extent of oxidation. Oxidation rates (pmol/min per mg heart protein) determined on 14C-labeled acid-soluble products suggest that oleic acid was oxidized 35-40% faster than elaidic acid by both male and female rat heart homogenates, whereas human heart homogenates oxidized these fatty acids at equal rates. Rates for female heart homogenates were somewhat higher than those for males in rats and humans. Rates of formation of 14CO2 were the same for each acid in rat and human heart tissue. Comparative rates of formation of oxidation products expressed as oleic/elaidic ratios from parallel incubations confirm that preferential oxidation of oleic acid occurred with rat heart homogenates, but not with the human heart homogenates. These data suggest that the presence of the trans double bond in elaidic acid does not impair its utilization for energy by human heart muscle.     

Fatty acid oxidation in human and rat heart. Comparison of cell-free and cellular systems

Oxidation rates of palmitate and activities of the mitochondrial marker enzymes cytochrome c oxidase and citrate synthase have been determined in homogenates, isolated mitochondria and slices of human and rat heart and in calcium-tolerant rat cardiac myocytes. Homogenates and mitochondria from rat heart showed a 6- and 2.5-fold higher palmitate oxidation rate than the corresponding preparations from human heart. From the palmitate oxidation rates and cytochrome c oxidase and citrate synthase activities as parameters, the mitochondrial protein contents of human and rat heart were calculated to be about 18 and 45 mg/g wet weight, respectively. Based on citrate synthase activities, the fatty acid oxidation rates were about the same in homogenates and isolated mitochondria, much lower in myocytes and lowest in slices. In the cellular systems the palmitate molecule was more completely oxidized than in homogenates or isolated mitochondria. Fatty acid oxidation rates were concentration-dependent in slices, but not with myocytes. With the cellular systems, palmitate oxidation was synergistically stimulated by the addition of carnitine, coenzyme A and ATP to the incubation medium. This stimulation could be attributed only partly to an increased oxidation in damaged cells.     

Studies on the peroxisomal oxidation of palmitate and lignocerate in rat liver

We have investigated the pathways involved in the peroxisomal oxidation of palmitate and lignocerate, measured as the cyanide-insensitive formation of acetyl units, in rat-liver homogenates. The peroxisomal beta-oxidation of both fatty acids is dependent on the presence of ATP, coenzyme A, NAD+ and Mg2+. However, there is a striking difference in the dependence of the rate of oxidation of the two substrates on the concentration of the individual cofactors, especially ATP. The peroxisomal beta-oxidation of lignocerate was inhibited to a progressively greater extent by increasing concentrations of palmitate and vice versa. Activation of lignoceric acid to lignoceroyl-CoA, however, was not inhibited by increasing concentrations of palmitate, and vice versa. It can be concluded that the peroxisomal palmitate and lignocerate beta-oxidation pathways differ in at least one enzymic reaction (the synthetase), but that the two pathways share at least one common step.     

Acyl-Coenzyme A synthetase and fatty acid oxidation in rat liver peroxisomes.

Rat liver peroxisomes oxidized palmitate in the presence of ATP, CoA and NAD+, and the rate of palmitate oxidation exceeded that of palmitoyl-CoA oxidation. Acyl-CoA synthetase [acid: CoA ligase (AMP-forming); EC 6.2.1.3] was found in peroxisomes. The substrate specificity of the peroxisomal synthetase towards fatty acids with various carbon chain lengths was similar to that of the microsomal enzyme. The peroxisomal synthetase activity toward palmitate (40--100 nmol/min per mg protein) was higher than the rate of palmitate oxidation by the peroxisomal system (0.7--1.7 nmol/min per mg protein). The data show that peroxisomes activate long chain fatty acids and oxidize their acyl-CoA derivatives.