Developmental changes in the activities of peroxisomal and mitochondrial beta-oxidation in chicken liver

The activities of peroxisomal and mitochondrial beta-oxidation and carnitine acyltransferases changed during the process of development from embryo to adult chicken, and the highest activities of peroxisomal beta-oxidation, palmitoyl-CoA oxidase, and carnitine acetyltransferase were found at the hatching stage of the embryo. The profiles of these alterations were in agreement with those of the contents of triglycerides and free fatty acids in the liver. The highest activities of mitochondrial beta-oxidation and palmitoyl-CoA dehydrogenase were observed at the earlier stages of the embryo; then the activities decreased gradually from embryo to adult chicken. The ratio of activities of carnitine acetyltransferase in peroxisomes and mitochondria (peroxisomes/mitochondria) increased from 0.54 to 0.82 during the development from embryo to adult chicken. The ratio of activities of carnitine palmitoyltransferase decreased from 0.82 to 0.25 during the development. The affinity of fatty acyl-CoA dehydrogenase toward the medium-chain acyl-CoAs (C6 and C8) was high in the embryo and decreased with development, whereas the substrate specificity of fatty acyl-CoA oxidase did not change. The substrate specificity of mitochondrial carnitine acyltransferases did not change with development. The affinity of peroxisomal carnitine acyltransferases toward the long-chain acyl-CoAs (C10 to C16) was high in the embryo, but low in adult chicken.     

Uptake, metabolism and release of carnitine and acylcarnitines in the perfused rat liver

The uptake and release of carnitine and isovalerylcarnitine have been studied in the perfused rat liver. Labelled carnitine accumulates in rat livers perfused with 50 or 500 microM [3H]carnitine. When alpha-ketoisocaproate (5 mM) is added to the perfusate after 30 min of perfusion, the net uptake of carnitine in the liver stops, and there is even a decrease in liver radioactivity. The decrease in liver carnitine can be attributed to an enhanced formation and efflux to the perfusate of short-chain acylcarnitines. Thin-layer chromatography of liver and perfusate extracts showed that efflux rates for branched-chain acylcarnitines (isovalerylcarnitine) formed are at least 2.5-fold the efflux rate for carnitine. Acetylcarnitine is released about twice as fast as carnitine from the liver. Perfusion with 50 microM [3H]isovalerylcarnitine showed that the influx rate of isovalerylcarnitine exceeds that of carnitine 1.5-fold. Since the efflux rate is still higher, a net loss of carnitine from the liver to the perfusate will result when branched-chain acylcarnitines are formed in the perfused liver. The addition of 500 microM unlabelled carnitine to the perfusate does not influence the release of labelled carnitine or acylcarnitines from the liver, showing that uptake and release are independent processes. Isovalerylcarnitine accumulates faster than carnitine does, also in the perfused rat heart. A mechanism for the development of secondary carnitine deficiencies associated with organic acidemia is proposed.     

Promoting lipid utilization with l-carnitine to improve oocyte quality

Successful embryo and fetal development is dependent on the quality of the oocyte from which it was derived. Several studies to date have demonstrated the link between appropriate metabolism and sufficient ATP production with oocyte quality and preimplantation embryo development. Metabolism of fatty acids for the purpose of synthesizing ATP occurs within mitochondria via β-oxidation and entry of fatty acids into this organelle is the rate-limiting step in this process. Transport of activated fatty acids into mitochondria is catalyzed by carnitine palmitoyl transferase-I (CPTI) which also requires the metabolite carnitine. Once inside the mitochondrial matrix, fatty acids are broken down into acetyl CoA molecules which are further metabolized via the TCA cycle and electron transport chain to produce ATP. The potential to improve oocyte quality by modulating fatty acid metabolism and β-oxidation with carnitine in culture media formulations or via dietary supplementation has received little attention. This review summarizes studies to date investigating the developmental importance of β-oxidation through the use of metabolic inhibitors and whether regulation by carnitine, in vitro or in vivo, has beneficial effects on oocyte and embryo development. Overall, there is little evidence to date that dietary carnitine can improve oocyte quality or female fertility; however inclusion of l-carnitine to in vitro oocyte maturation and embryo growth media improves embryo outcomes, most likely by supplying the oocyte and embryo with an essential co-factor required to utilize fatty acids.     

Acid soluble, short chain esterified and free carnitine in the liver, heart, muscle and brain of pre and post hatched chicks

1. The behaviour of total acid soluble, short chain esterified and free carnitine in the liver, heart, muscle and brain of chick embryos between 11th and 21st day of development and of 8 and 180-day-old chicks is described. 2. Total acid soluble carnitine fluctuates around the same levels in the brain, liver and muscle until 18th day of development, whereas it attains a peak on that day in the heart. At hatching compared to 18th day, it suddenly increases three times in the muscle, drops not significantly in the heart and brain, but sharply in the liver (-40%). However the levels are always higher than those of the grown chick in the brain but lower in the other tissues. 3. Free carnitine levels are almost constant in all tissues during the embryonic life; if compared to adult ones, they are very much lower in the liver, heart and muscle, but higher in the brain, even in 8 day-old chick. 4. Short chain esterified, carnitine reaches a maximum on 18th day of egg incubation in the liver, brain and heart; in the muscle it stays on constant levels until this day and then rapidly increases so that at hatching it doubles the values. 5. The short chain esterified to free carnitine percentage ratio peaks in all tissues on 18th day of development, attaining figures which are well above those determined in the grown chick.     

gamma-Butyrobetaine as a specific antagonist for carnitine in the development of the early chick embryo

The effect of γ-butyrobetaine alone and with the addition of carnitine on the development of the early excised chick embryo has been studied. γ-Butyrobetaine in appropriate amounts exerts an inhibitory effect which can be relieved or annulled by the inclusion of appropriate amounts of carnitine. This has been interpreted as a metabolite-antimetabolite relationship, in which the normal metabolite, carnitine, is antagonized by the structurally closely related γ-butyrobetaine, and is regarded as evidence of an important role of carnitine in the metabolism of the developing chick embryo.     

beta-lactam antibiotics as substrates for OCTN2, an organic cation/carnitine transporter

Therapeutic use of cephaloridine, a beta-lactam antibiotic, in humans is associated with carnitine deficiency. A potential mechanism for the development of carnitine deficiency is competition between cephaloridine and carnitine for the renal reabsorptive process. OCTN2 is an organic cation/carnitine transporter that is responsible for Na(+)-coupled transport of carnitine in the kidney and other tissues. We investigated the interaction of several beta-lactam antibiotics with OCTN2 using human cell lines that express the transporter constitutively as well as using cloned human and rat OCTN2s expressed heterologously in human cell lines. The beta-lactam antibiotics cephaloridine, cefoselis, cefepime, and cefluprenam were found to inhibit OCTN2-mediated carnitine transport. These antibiotics possess a quaternary nitrogen as does carnitine. Several other beta-lactam antibiotics that do not possess this structural feature did not interact with OCTN2. The interaction of cephaloridine with OCTN2 is competitive with respect to carnitine. Interestingly, many of the beta-lactam antibiotics that were not recognized by OCTN2 were good substrates for the H(+)-coupled peptide transporters PEPT1 and PEPT2. In contrast, cephaloridine, cefoselis, cefepime, and cefluprenam, which were recognized by OCTN2, did not interact with PEPT1 and PEPT2. The interaction of cephaloridine with OCTN2 was Na(+)-dependent, whereas the interaction of cefoselis and cefepime with OCTN2 was largely Na(+)-independent. Furthermore, the Na(+)-dependent, OCTN2-mediated cellular uptake of cephaloridine could be demonstrated by direct uptake measurements. These studies show that OCTN2 plays a crucial role in the pharmacokinetics and therapeutic efficacy of certain beta-lactam antibiotics such as cephaloridine and that cephaloridine-induced carnitine deficiency is likely to be due to inhibition of carnitine reabsorption in the kidney.     

Altered carnitine homeostasis is associated with decreased mitochondrial function and altered nitric oxide signaling in lambs with pulmonary hypertension

Utilizing aortopulmonary vascular graft placement in the fetal lamb, we have developed a model (shunt) of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. Our previous studies have identified a progressive development of endothelial dysfunction in shunt lambs that is dependent, at least in part, on decreased nitric oxide (NO) signaling. The purpose of this study was to evaluate the possible role of a disruption in carnitine metabolism in shunt lambs and to determine the effect on NO signaling. Our data indicate that at 2 wk of age, shunt lambs have significantly reduced expression (P < 0.05) of the key enzymes in carnitine metabolism: carnitine palmitoyltransferases 1 and 2 as well as carnitine acetyltransferase (CrAT). In addition, we found that CrAT activity was inhibited due to increased nitration. Furthermore, free carnitine levels were significantly decreased whereas acylcarnitine levels were significantly higher in shunt lambs (P < 0.05). We also found that alterations in carnitine metabolism resulted in mitochondrial dysfunction, since shunt lambs had significantly decreased pyruvate, increased lactate, and a reduced pyruvate/lactate ratio. In pulmonary arterial endothelial cells cultured from juvenile lambs, we found that mild uncoupling of the mitochondria led to a decrease in cellular ATP levels and a reduction in both endothelial NO synthase-heat shock protein 90 (eNOS-HSP90) interactions and NO signaling. Similarly, in shunt lambs we found a loss of eNOS-HSP90 interactions that correlated with a progressive decrease in NO signaling. Our data suggest that mitochondrial dysfunction may play a role in the development of endothelial dysfunction and pulmonary hypertension and increased pulmonary blood flow.     

Inhibition of cell-cell adhesion and morphogenesis of Dictyostelium by carnitine.

Carnitine (gamma-trimethylammonium beta-hydroxy-butyric acid) possesses the novel property of preventing cell aggregation elicited by clusterin or by fibrinogen (I.B. Fritz and K. Burdzy, J. Cell. Physiol., 140:18-28 [1989]). In investigations reported here, we show that carnitine also affects cell-cell adhesion in Dictyostelium discoideum, a cellular slime mold whose cells interact in specific and complex manners during discrete stages of development. Two types of cell adhesion systems sequentially appear on the surface of developing Dictyostelium cells, involving the surface glycoprotein gp24 which mediates EDTA-sensitive binding sites, and the surface glycoprotein gp80 which mediates the EDTA-resistant binding sites. Addition of increasing concentrations of D(+)-carnitine and L(-)-carnitine resulted in a progressive inhibition of both the EDTA-sensitive binding sites and the EDTA-resistant binding sites of Dictyostelium cells at different stages of development. In contrast, comparable or higher concentrations of choline, acetyl-beta-methylcholine, or deoxycarnitine had no detectable effects on cell aggregation. Concentrations of carnitine required for 50% inhibition of EDTA-resistant adhesion sites were found to be dependent upon levels of gp80 expressed by Dictyostelium, with greatest inhibition by carnitine of reassociation of cells containing the lowest levels of gp80. Removal of carnitine from cells by washing resulted in the rapid restoration of the ability of Dictyostelium to form aggregates and to resume normal development. We discuss possible mechanisms by which carnitine inhibits the aggregation of cells.     

Crystal structure of carnitine acetyltransferase and implications for the catalytic mechanism and fatty acid transport

Carnitine acyltransferases have crucial roles in the transport of fatty acids for beta-oxidation. Dysregulation of these enzymes can lead to serious diseases in humans, and they are targets for therapeutic development against diabetes. We report the crystal structures of murine carnitine acetyltransferase (CRAT), alone and in complex with its substrate carnitine or CoA. The structure contains two domains. Surprisingly, these two domains share the same backbone fold, which is also similar to that of chloramphenicol acetyltransferase and dihydrolipoyl transacetylase. The active site is located at the interface between the two domains. Carnitine and CoA are bound in deep channels in the enzyme, on opposite sides of the catalytic His343 residue. The structural information provides a molecular basis for understanding the catalysis by carnitine acyltransferases and for designing their inhibitors. Specifically, our structural information suggests that the substrate carnitine may assist the catalysis by stabilizing the oxyanion in the reaction intermediate.     

PPAR-γ Regulates Carnitine Homeostasis and Mitochondrial Function in a Lamb Model of Increased Pulmonary Blood Flow

Objective

Carnitine homeostasis is disrupted in lambs with endothelial dysfunction secondary to increased pulmonary blood flow (Shunt). Our recent studies have also indicated that the disruption in carnitine homeostasis correlates with a decrease in PPAR-γ expression in Shunt lambs. Thus, this study was carried out to determine if there is a causal link between loss of PPAR-γ signaling and carnitine dysfunction, and whether the PPAR-γ agonist, rosiglitazone preserves carnitine homeostasis in Shunt lambs.

Methods and Results

siRNA-mediated PPAR-γ knockdown significantly reduced carnitine palmitoyltransferases 1 and 2 (CPT1 and 2) and carnitine acetyltransferase (CrAT) protein levels. This decrease in carnitine regulatory proteins resulted in a disruption in carnitine homeostasis and induced mitochondrial dysfunction, as determined by a reduction in cellular ATP levels. In turn, the decrease in cellular ATP attenuated NO signaling through a reduction in eNOS/Hsp90 interactions and enhanced eNOS uncoupling. In vivo, rosiglitazone treatment preserved carnitine homeostasis and attenuated the development of mitochondrial dysfunction in Shunt lambs maintaining ATP levels. This in turn preserved eNOS/Hsp90 interactions and NO signaling.

Conclusion

Our study indicates that PPAR-γ signaling plays an important role in maintaining mitochondrial function through the regulation of carnitine homeostasis both in vitro and in vivo. Further, it identifies a new mechanism by which PPAR-γ regulates NO signaling through Hsp90. Thus, PPAR-γ agonists may have therapeutic potential in preventing the endothelial dysfunction in children with increased pulmonary blood flow.     

Effect of exogenous carnitine on carnitine homeostasis in the rat

The interaction of exogenous carnitine with whole body carnitine homeostasis was characterized in the rat. Carnitine was administered in pharmacologic doses (0-33.3 mumols/100 g body weight) by bolus, intravenous injection, and plasma, urine, liver, skeletal muscle and heart content of carnitine and acylcarnitines quantitated over a 48 h period. Pre-injection urinary carnitine excretion was circadian as excretion rates were increased 2-fold during the lights-off cycle as compared with the lights-on cycle. Following carnitine administration, there was an increase in urinary total carnitine excretion which accounted for approx. 60% of the administered carnitine at doses above 8.3 mumols/100 g body weight. Urinary acylcarnitine excretion was increased following carnitine administration in a dose-dependent fashion. During the 24 h following administration of 16.7 mumols [14C]carnitine/100 g body weight, urinary carnitine specific activity averaged only 72 +/- 4% of the injection solution specific activity. This dilution of the [14C]carnitine specific activity suggests that endogenous carnitine contributed to the increased net urinary carnitine excretion following carnitine administration. 5 min after administration of 16.7 mumol carnitine/100 g body weight approx. 80% of the injected carnitine was in the extracellular fluid compartment and 5% in the liver. Plasma, liver and soleus total carnitine contents were increased 6 h after administration of 16.7 mumols carnitine/100 g body weight. 6 h post-administration, 37% of the dose was recovered in the urine, 12% remained in the extracellular compartment, 9% was in the liver and 22% was distributed in the skeletal muscle. In liver and plasma, short chain acylcarnitine content was increased 5 min and 6 h post injection as compared with controls. Plasma, liver, skeletal muscle and heart carnitine contents were not different from control levels 48 h after carnitine administration. The results demonstrate that single, bolus administration of carnitine is effective in increasing urinary acylcarnitine elimination. While liver carnitine content is doubled for at least 6 h following carnitine administration, skeletal muscle and heart carnitine pools are only modestly perturbed following a single intravenous carnitine dose. The dilution of [14C]carnitine specific activity in the urine of treated animals suggests that tissue-blood carnitine or acylcarnitine exchange systems contribute to overall carnitine homeostasis following carnitine administration.     

Clearance of exogenous carnitine in bovine semen: Potential diagnosis of epididymal function and patency of the ductus deferens

Carnitine content in the ejaculate depends mainly on the capability of the epididymis wall to transfer carnitine from the blood and on the patency of ejaculatory ductus systems. An elevation of carnitine in semen subsequent to an intravenous injection of carnitine is expected. Intravenous injections of carnitine (L-isomer and DL-isomers) caused a significant (P <0.05) elevation (more than 10-fold) in blood carnitine. However, carnitine injection failed to increase net secretion of carnitine into the ejaculate and blood elimination half-life was 2.3 hours. Mean concentrations of carnitine in the electroejaculate (3.0 nmoles/ml) were significantly lower than in the ejaculate following natural mating (180 nmoles/ml). Vasectomy decreased net carnitine per ejaculate to about 1/5 the prevasectomy value, when ejaculate was collected following natural mating. However, vasectomy did not affect carnitine concentrations in semen collected by electroejaculation. Twenty-one percent of the carnitine in semen originated in the accessory glands and 79% in the epididymides. Carnitine in the electroejaculate was originated almost exclusively in the accessory glands. It was concluded that the diagnostic value of carnitine in semen is limited. Some considerations are: secretion of carnitine is not organ specific, there are large individual variations, there is a negative effect of electroejaculation, and a carnitine loading dose technique is not feasible. However, there is a diagnostic potential in using carnitine assay to detect epididymides occlusion, but only when ejaculate is collected by an artificial vagina.     

Effects of carnitine on respiratory chain and metabolism of oxygen radical in mitochondria of liver after exhaustive running in training rat

The aim of the present study was to investigate the effect of carnitine on cellular respiratory chain and metabolism of oxygen radical in mitochondria of liver after exhaustive running in training rats. Forty male Wistar rats were randomly divided into 4 groups (n = 10): control, carnitine, training and training+carnitine groups. The training and training+carnitine groups received 6-week treadmill training, whereas carnitine and training+carnitine groups were administrated intragastrically with carnitine (300 mg/kg per d) for 6 weeks. After exhaustive running, all the groups were sacrificed to obtain liver samples, and liver mitochondria were extracted by differential centrifugation. Spectrophotometric analysis was used to evaluate activities of respiratory chain complexes (RCC) I-IV, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and the content of malondialdehyde (MDA) in the liver mitochondria. The results showed that, compared with the control group, the carnitine group exhibited increased RCCIV activity (P < 0.05), the training group exhibited increased RCCI, RCCIII and RCCIV activities, and the training+carnitine group showed increased RCCI-IV activities (P < 0.05 or P < 0.01). Moreover, RCCI and RCCIV activities in the training+carnitine group were higher than those in the carnitine and training groups (P < 0.05 or P < 0.01). Compared with the control group, the training+carnitine group showed increased SOD activity (P < 0.01), the carnitine, training and training+carnitine groups showed increased GSH-Px activities (P < 0.05, P < 0.01), and the training and training+carnitine groups showed decreased MDA contents (P < 0.05, P < 0.01). The training+carnitine group showed increased GSH-Px activity compared to that in the carnitine group (P < 0.01).The SOD activity in the training+carnitine group was higher than those in the carnitine and training groups (P < 0.05 or P < 0.01), and the MDA level in the the training+carnitine group was lower than those in the carnitine and training groups (P < 0.01). These results suggest that training and carnitine can increase the function of respiratory chain and antioxidant capacity in liver mitochondria, and the improving effects of training and carnitine can be synergistic.     

Hepatic release of carnitine: effect of increased concentration by clofibrate treatment.

The release of carnitine is an important metabolic function of the liver. In the present study, we have investigated the effect of increased carnitine concentration on the hepatic release of carnitine. Hepatic carnitine concentration was increased in rats by clofibrate treatment. Release of carnitine was investigated as its efflux from perfused liver and its secretion into bile. A significantly smaller proportion of the hepatic pool of carnitine was released into the perfusion medium when carnitine concentration was increased by clofibrate treatment. However, the amount of carnitine released (nmol/g liver) was comparable to that of control rats. Increased carnitine concentration by clofibrate treatment also did not affect the rate of biliary secretion of carnitine. In control rats, nearly 50% of the released carnitine, in both the perfusion medium and bile, was acylcarnitine whereas in clofibrate-treated rats 35% of the released carnitine was acylcarnitine. Release into the perfusion medium was the major route for the hepatic export of carnitine. We conclude that when hepatic carnitine concentration is increased by clofibrate treatment, a smaller proportion of the hepatic carnitine pool is released, but the amount of carnitine released (nmol/g liver) is not greatly different than that from control animals.     

Carnitine and carnitine esters in rat bile and human duodenal fluid

The recent discovery of carnitine and its esters in rat bile has led to much speculation about its role. The objectives of these studies were to investigate the origin of carnitine esters in rat bile and to study the presence of carnitine in human bile-rich duodenal fluid. Bile was collected from chow-fed (n = 11), fasted (72 h, n = 6), and fasted plus 2-tetradecylglycidic acid administered (72 h, n = 5) male adult rats under sodium pentobarbital anaesthesia. Carnitine and carnitine ester content was measured in the bile and compared with serum and liver carnitine. Bile from fed rats was found to contain 80% acylcarnitine, one-third of this as long chain carnitine esters. Fasting caused no change in the secretion rate of acylcarnitine into the bile, although long chain carnitine ester secretion almost doubled. Conversely, 2-tetradecylglycidic acid treatment caused a decrease in long chain carnitine ester secretion into bile. Duodenal fluid was collected from patients with suspected cholelithiasis (n = 10) before and after pancreozymin-cholecystokinin injection. Although carnitine concentration was variable, it was consistently 80% esterified. These data associate bile carnitine with hepatic carnitine metabolism and establish the presence of carnitine and carnitine esters in the human intestinal lumen.     

Regulation of carnitine status in ruminants and efficacy of carnitine supplementation on performance and health aspects of ruminant livestock: a review

Carnitine has long been known to play a critical role for energy metabolism. Due to this, a large number of studies have been carried out to investigate the potential of supplemental carnitine in improving performance of livestock animals including ruminants, with however largely inconsistent results. An important issue that has to be considered when using carnitine as a feed additive is that the efficacy of supplemental carnitine is probably dependent on the animal’s carnitine status, which is affected by endogenous carnitine synthesis, carnitine uptake from the gastrointestinal tract and carnitine excretion. The present review aims to summarise the current knowledge of the regulation of carnitine status and carnitine homeostasis in ruminants, and comprehensively evaluate the efficacy of carnitine supplementation on performance and/or health in ruminant livestock by comparing the outcomes of studies with carnitine supplementation in dairy cattle, growing and finishing cattle and sheep. While most of the studies show that supplemental carnitine, even in ruminally unprotected form, is bioavailable in ruminants, its effect on either milk or growth performance is largely disappointing. However, supplemental carnitine appears to be a useful strategy to offer protection against ammonia toxicity caused by consumption of high levels of non-protein N or forages with high levels of soluble N both, in cattle and sheep.     

Effect of vitamin B-12 deficiency on the hepatic tissue concentration of acyl carnitines.

Concentrations of carnitine, acetyl carnitine, propionyl carnitine, and long chain acyl carnitines have been measured in hepatic tissue of normal and vitamin B-12 deficient rats using radiolabelled butyrobetaine to label carnitine pools. Increased levels of propionyl carnitine were seen in the livers of vitamin B-12 deprived animals when compared to those from normal animals. Methylmalonyl carnitine was not detected in the B-12 deprived animals. Free carnitine levels were no different in the livers from the B-12 deprived animals than from the normal control animals.     

Purification and properties of peroxisomal carnitine palmitoyltransferase in chick embryo liver

Peroxisomal carnitine palmitoyltransferase was purified by solubilization using Tween 20 and KCl from the large granule fraction of the liver of clofibrate-treated chick embryo, DEAE-Sephacel and blue Sepharose CL-6B column chromatography. The peroxisomal carnitine palmitoyltransferase was an Mr 64,000 polypeptide; the mitochondrial carnitine palmitoyltransferase had a subunit molecular weight of 69,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The carnitine acetyltransferase was an Mr 64,000 polypeptide. Antibody against purified peroxisomal carnitine palmitoyltransferase reacted only with peroxisomal carnitine palmitoyltransferase, but not with mitochondrial carnitine palmitoyltransferase or carnitine acetyltransferase. In addition, anti-peroxisomal carnitine palmitoyltransferase reacted only with the protein in peroxisomes purified from chick embryo liver by sucrose density gradient centrifugation. Thus, it was confirmed that purified peroxisomal carnitine palmitoyltransferase was a peroxisomal protein. Compared with mitochondrial carnitine palmitoyltransferase, peroxisomal carnitine palmitoyltransferase was extremely resistant to inactivation by trypsin. The pH optimum of peroxisomal carnitine palmitoyltransferase was 8.5, differing from that of mitochondrial carnitine palmitoyltransferase. The Km value of peroxisomal carnitine palmitoyltransferase for palmitoyl-CoA (32 microM) was similar to that of the mitochondrial one, whereas those values for L-carnitine (140 microM), palmitoyl-L-carnitine (43 microM) and CoA (9 microM) were lower than those of mitochondrial carnitine palmitoyltransferase. Peroxisomal carnitine palmitoyltransferase exhibited similar substrate specificities in both the forward and reverse reactions, with the highest activity toward lauroyl derivatives. Furthermore, this enzyme showed relatively high affinities for long-chain acyl derivatives (C10-C16) and similar Km values (30-50 microM) for acyl-CoAs, acylcarnitine and CoA, and a constant Km value (approximately 150 microM) for carnitine. These results indicate that peroxisomal carnitine palmitoyltransferase played a role in the modulation of the intracellular CoA/long-chain acyl-CoA ratio at the hatching stage of chicken when long-chain fatty acids are actively oxidized in peroxisomes.