Inhibition of long-chain fatty acid activation by -bromopalmitate and phytanate

Mass spectrometric imaging of metabolites in kidney tissues from rats treated with furosemide

In the kidney, metabolic processes are different among the cortex (COR), outer medulla (OM), and inner medulla (IM). Using matrix-assisted laser desorption/ionization (MALDI) and imaging mass spectrometry (IMS), we examined the change of metabolites in the COR, OM, and IM of the rat kidney after furosemide treatment compared with vehicle-treated controls. Osmotic minipumps were implanted in male Sprague-Dawley rats to deliver 12 mg·day(-1)·rat(-1) of furosemide. Vehicle-treated (n = 14) and furosemide-treated (furosemide rats, n = 15) rats in metabolic cages received a fixed amount of rat chow (15 g·220 g body wt(-1)·day(-1) for each rat) with free access to water intake for 6 days. At day 6, higher urine output (32 ± 4 vs. 9 ± 1 ml/day) and lower urine osmolality (546 ± 44 vs. 1,677 ± 104 mosmol/kgH2O) were observed in furosemide rats. Extracts of COR, OM, and IM were analyzed by ultraperformance liquid chromatography coupled with quadrupole time-of-flight (TOF) mass spectrometry, where multivariate analysis revealed significant differences between the two groups. Several metabolites, including acetylcarnitine, betaine, carnitine, choline, and glycerophosphorylcholine (GPC), were significantly changed. The changes of metabolites were further identified by MALDI-TOF/TOF and IMS. Their spatial distribution and relative quantitation in the kidneys were analyzed by IMS. Carnitine compounds were increased in COR and IM, whereas carnitine and acetylcarnitine were decreased in OM. Choline compounds were increased in COR and OM but decreased in IM from furosemide rats. Betaine and GPC were decreased in OM and IM. Taken together, MALDI-TOF/TOF and IMS successfully provide the spatial distribution and relative quantitation of metabolites in the kidney.

Palmitate potentiation of glucose-induced insulin release: a study using 2-bromopalmitate

The mechanisms whereby fatty acids (FA) potentiate glucose-induced insulin secretion from the pancreatic beta cell are incompletely understood. In this study, the effects of palmitate on insulin secretion were investigated in isolated rat islets. Palmitate did not initiate insulin secretion at nonstimulatory glucose concentrations, but markedly stimulated insulin release at concentrations of glucose > or = 5.6 mmol/L. At concentrations of palmitate > or =0.5 mmol/L, the important determinant of the potency of the FA was its unbound concentration. At total concentrations < or = 0.5 mmol/L, both the total and unbound concentrations appeared important. Surprisingly, 2-bromopalmitate did not affect palmitate oxidation, but significantly diminished palmitate esterification into cellular lipids. Neither methyl palmitate, which is not activated into a long-chain acyl-CoA ester, nor 2-bromopalmitate affected glucose-stimulated insulin release. Further, 2-bromopalmitate partly inhibited the potentiating effect of palmitate. These results support the concept that FA potentiation of insulin release is mediated by FA-derived signals generated in the esterification pathway.

Palmitate acutely raises glycogen synthesis in rat soleus muscle by a mechanism that requires its metabolization (Randle cycle)

The acute effect of palmitate on glucose metabolism in rat skeletal muscle was examined. Soleus muscles from Wistar male rats were incubated in Krebs-Ringer bicarbonate buffer, for 1 h, in the absence or presence of 10 mU/ml insulin and 0, 50 or 100 microM palmitate. Palmitate increased the insulin-stimulated [(14)C]glycogen synthesis, decreased lactate production, and did not alter D-[U-(14)C]glucose decarboxylation and 2-deoxy-D-[2,6-(3)H]glucose uptake. This fatty acid decreased the conversion of pyruvate to lactate and [1-(14)C]pyruvate decarboxylation and increased (14)CO(2) produced from [2-(14)C]pyruvate. Palmitate reduced insulin-stimulated phosphorylation of insulin receptor substrate-1/2, Akt, and p44/42 mitogen-activated protein kinases. Bromopalmitate, a non-metabolizable analogue of palmitate, reduced [(14)C]glycogen synthesis. A strong correlation was found between [U-(14)C]palmitate decarboxylation and [(14)C]glycogen synthesis (r=0.99). Also, palmitate increased intracellular content of glucose 6-phosphate in the presence of insulin. These results led us to postulate that palmitate acutely potentiates insulin-stimulated glycogen synthesis by a mechanism that requires its metabolization (Randle cycle). The inhibitory effect of palmitate on insulin-stimulated protein phosphorylation might play an important role for the development of insulin resistance in conditions of chronic exposure to high levels of fatty acids.

Control of mitochondrial beta-oxidation flux

The control of mitochondrial beta-oxidation, including the delivery of acyl moieties from the plasma membrane to the mitochondrion, is reviewed. Control of beta-oxidation flux appears to be largely at the level of entry of acyl groups to mitochondria, but is also dependent on substrate supply. CPTI has much of the control of hepatic beta-oxidation flux, and probably exerts high control in intact muscle because of the high concentration of malonyl-CoA in vivo. beta-Oxidation flux can also be controlled by the redox state of NAD/NADH and ETF/ETFH(2). Control by [acetyl-CoA]/[CoASH] may also be significant, but it is probably via export of acyl groups by carnitine acylcarnitine translocase and CPT II rather than via accumulation of 3-ketoacyl-CoA esters. The sharing of control between CPTI and other enzymes allows for flexible regulation of metabolism and the ability to rapidly adapt beta-oxidation flux to differing requirements in different tissues.

Metabolism of 4-hydroxynonenal, a cytotoxic product of lipid peroxidation, in rat precision-cut liver slices

4-Hydroxy-2-nonenal (HNE) is a major aldehydic product of lipid peroxidation known to exert several biological and cytotoxic effects. The in vitro metabolism of [4-(3)H]-HNE by rat precision-cut liver slices was investigated. Liver slices rapidly metabolize HNE - about 85% of 0.1 microM [4-(3)H]-HNE was degraded within 5 min of incubation. The main metabolites of HNE identified were 4-hydroxynonenoic acid (HNA), glutathione-HNE-conjugate (HNE-GSH), glutathione-1,4-dihydroxynonene-conjugate (DHN-GSH) and cysteine-HNE-conjugate (HNE-CYS). Whereas glutathione conjugation demonstrated saturation kinetics (K(m)=412.2+/-152.7 microM and V(max)=12.3+/-2.5 nmol h(-1) per milligram protein), HNA formation was linear up to 500 microM HNE in liver slices. In contrast to previous reports, no trace of the corresponding alcohol of the HNE, 1,4-dihydroxynon-2-ene was detected in the present study. Furthermore, the beta-oxidation of HNA including the formation of tritiated water was demonstrated. The identification of 4-hydroxy-9-carboxy-2-nonenoic acid and 4,9-dihydroxynonanoic acid demonstrated that omega-oxidation significantly contributes to the biotransformation of HNE in liver slices.

Skeletal muscle lipids and glycogen mask substrate competition (Randle cycle)

The glucose-free fatty acid (FFA) cycle (Randle) was examined in soleus muscle, a red muscle with a high lipid oxidation rate, and extensor digitorum longus (EDL) muscle, a white muscle with a low lipid oxidation rate, using a carnitine palmethyltransferase (CPT-I) inhibitor as a probe. Exogenous palmitate by itself had little if any effect on glycolysis or glycogen accumulation in the two muscle types. The CPT-I inhibitor markedly decreased glycogen accumulation in both muscles (from fed rats), but increased glycolysis (lactate formation) and glucose oxidation to carbon dioxide only in the red muscle. When the muscles were made more dependent on FFA oxidation by prior fasting or exercise, the CPT-I stimulatory effect on glycolysis and glucose oxidation in white muscle was unmasked. In conclusion, the competition between lipid and carbohydrate utilization (Randle cycle) is easily demonstrated in both red and white muscle using a CPT-I inhibitor as a probe. The difficulties encountered in showing this competition in other studies using exogenous FFA may be explained by a combination of factors, including (1) low tissue lipid oxidation rates, (2) competition between exogenous and endogenous lipids such that provision of exogenous lipids fails to increase overall lipid oxidation, and (3) preferential utilization of exogenous glucose with glycogen sparing in the presence of FFA.

Evidence for dissociation of gluconeogenesis stimulated by non-esterified fatty acids and changes in fructose 2,6-bisphosphate in cultured rat hepatocytes

In order to examine the role of fructose 2,6-bisphosphate (Fru-2,6-P2) in non-esterified-fatty-acid-stimulated gluconeogenesis, Fru-2,6-P2 levels were measured in cultured rat hepatocytes under conditions mimicking the fasted state. After addition of either 1.5 mM-palmitate or 10 nM-glucagon, [U-14C]lactate incorporation into glucose increased 2-fold, but only glucagon suppressed Fru-2,6-P2. Prevention of palmitate oxidation with a carnitine palmitoyltransferase-I inhibitor (2-bromopalmitate) diminished glucose production and Fru-2,6-P2 levels. Addition of exogenous glucose to the media increased Fru-2,6-P2 in a dose-related manner, which was further augmented by addition of palmitate. When Fru-2,6-P2 levels were examined in cells cultured under conditions mimicking the fed state (significantly higher basal Fru-2,6-P2 levels and lower glucose production), palmitate oxidation was associated with a significant fall in Fru-2,6-P2. In conclusion, the present studies have demonstrated a dissociation between fatty-acid-stimulated gluconeogenesis and changes in Fru-2,6-P2 in cultured rat hepatocytes. Further experiments suggest that the accumulation of intracellular hexose 6-phosphate as a result of fatty-acid-stimulated gluconeogenesis masks a putative inhibitory effect of fatty acids on Fru-2,6-P2 concentrations.

Induction of aP2 gene expression by nonmetabolized long-chain fatty acids

Long-chain fatty acids (FA) have been shown to regulate expression of the gene for the adipocyte FA-binding protein aP2. We examined whether this effect was exerted by FA themselves or by a FA metabolite. The alpha-bromo derivative of palmitate, an inhibitor of FA oxidation, was synthesized in the radioactive form, and its metabolism was investigated and correlated with its ability to induce aP2 in Ob1771 preadipocytes. alpha-Bromopalmitate was not utilized by preadipocytes. It was not cleared from the medium over a 24-hr period and was not incorporated into cellular lipids. Short incubations indicated that alpha-bromopalmitate exchanged across the preadipocyte membrane but remained in the free form inside the cell. In line with this, preadipocyte homogenates did not activate alpha-bromopalmitate to the acyl form. However, although it was not metabolized, bromopalmitate was much more potent than native FA in inducing aP2 gene expression. Induction exhibited the characteristics previously described for native FA, indicating that a similar if not identical mechanism was involved. The data indicated that induction of aP2 was exerted by unprocessed FA. Finally, in contrast to preadipocytes, adipocytes metabolized bromopalmitate. This reflected increased activity with cell differentiation of a palmitoyl-CoA synthase that could activate palmitate and bromopalmitate at about one-fifth the rate for palmitate. In preadipocytes, the predominant fatty-acyl-CoA synthase, arachidonyl-CoA synthase, had very low affinity for both FA. Increased activity of the palmitoyl-CoA synthase, which has a wider substrate range, is likely to be important for initiation of lipid deposition.

2-Bromopalmitoyl-CoA and 2-bromopalmitate: promiscuous inhibitors of membrane-bound enzymes

2-Bromopalmitate and 2-bromopalmitoyl-CoA have been shown to inhibit a variety of enzymes and proteins associated with lipid metabolism. We found that both of the brominated compounds were non-competitive inhibitors of two microsomal activities of triacylglycerol biosynthesis, the mono- and diacylglycerol acyltransferases. With both compounds, the calculated Ki values were lower than the Km value for the palmitoyl-CoA substrate. In addition to inhibiting two other lipid synthetic activities, fatty acid CoA ligase and glycerol-3-P acyltransferase, 2-bromopalmitate and 2-bromopalmitoyl-CoA also inhibited two microsomal enzyme activities that are not related to lipid metabolism, NADPH cytochrome-c reductase and glucose-6-phosphatase. Inhibition of the three acyltransferases and fatty acid CoA ligase could be overcome by the addition of phospholipid vesicles, and 2-bromo[14C]palmitate readily labeled a large number of membrane-bound proteins as well as cytosolic proteins that had been solubilized in SDS. Thus, it appears likely that the inhibitory properties of the brominated compounds strongly depend on the effective concentration of the inhibitor within membranes rather than on any specific affinity for an acyl-chain binding region of the enzyme.

Inhibition of long-chain acyl-CoA synthetase by the peroxisome proliferator perfluorodecanoic acid in rat hepatocytes

Perfluorodecanoic acid (PFDA) is a potent peroxisome proliferator and is known to affect hepatic lipid metabolism in rats. The effects of PFDA on fatty acid utilization were examined in isolated rat hepatocyte suspensions and in rat liver mitochondria and microsomes. PFDA inhibited the oxidation of palmitic acid but not octanoic or pyruvic acids when hepatocytes were incubated with 1 mM PFDA. At this PFDA concentration the esterification of palmitic acid into triacylglycerols was also reduced. The activity of long-chain acyl-CoA synthetase (ACS), an enzyme essential for both oxidation and esterification of fatty acids, was reduced in hepatocytes incubated with 1 mM PFDA. Carnitine palmitoyltransferase (CPT), an important enzyme for the oxidation of long-chain fatty acids, was not altered in hepatocytes incubated with this PFDA concentration. In rat liver mitochondria, palmitate oxidation and ACS activity were reduced significantly (P less than 0.01) at a PFDA concentration that had no effect on CPT activity. The inhibition of ACS by PFDA was similar in liver mitochondria and microsome preparations. In mitochondria incubated with PFDA, the inhibition of ACS appears to be noncompetitive for the substrates palmitic acid and CoA. However, the ACS inhibition by PFDA appeared to be competitive for the ATP binding site of the enzyme. Several chain length perfluorinated fatty acids were examined for their ability to inhibit mitochondrial ACS. Short-chain perfluorinated fatty acids (perfluoroproprionic and -butyric acid) did not inhibit ACS activity. However, medium-chain perfluorinated acids (perfluorooctanoic, -ananoic and -decanoic acid) were found to be potent inhibitors of ACS in isolated mitochondria. Whether ACS inhibition is causally related to PFDA-induced peroxisome proliferation and altered lipid metabolism seen in vivo is yet to be determined.

The effect of dietary alpha-bromopalmitate on blood lipids in the rat

When alpha-bromopalmitate was fed to rats for 9-30 days, the level of serum triacylglycerol increased up to 2-fold over the concentration of controls. alpha-Bromopalmitate treatment had no effect on concentration of complex lipids in liver, while the triacylglycerol level in heart was significantly enhanced. From metabolic studies using isolated hepatocytes and liver microsomes, it is suggested that the increased serum triacylglycerol level after alpha-bromopalmitate feeding is mainly due to reduced fatty acid oxidation in both liver and peripheral tissues, and to a lesser extent, to inhibited fatty acid uptake and esterification.

Prevention of peroxisomal proliferation by carnitine palmitoyltransferase inhibitors in cultured rat hepatocytes and in vivo

1. The induction of peroxisomal beta-oxidation activities by bezafibrate in cultured rat hepatocytes and in the rat in vivo was prevented by inhibitors of carnitine acyltransferase, e.g. 2-bromopalmitate, 2-[5-(4-chlorophenyl)pentyl]oxirane-2-carboxylate or 2-tetradecylglycidic acid. 2. The prevention of peroxisomal proliferation by carnitine palmitoyltransferase inhibitors could not be accounted for by inhibition of mitochondrial beta-oxidation, since 2-bromo-octanoate, acting as an inhibitor of beta-oxidation, did not prevent the induction of peroxisomal activities in cultured rat hepatocytes. 3. The putative role of the acylcarnitine derivative of bezafibrate was analysed by studying the formation of bezafibroylcarnitine with bezafibroyl-CoA as substrate. However, no bezafibroylcarnitine formation was demonstrated in the presence of rat liver preparations capable of catalysing transfer to carnitine of medium- or long-chain fatty acids. 4. The prevention of peroxisomal proliferation by carnitine acyltransferase inhibitors may help in dissecting the causal relationship between the multiple effects mediated by peroxisomal proliferators.

In vitro effects of alpha-bromopalmitate on metabolism of essential fatty acids studied in isolated rat hepatocytes: sex differences

alpha-Bromopalmitate was shown to have a far more pronounced effect on metabolism of labelled linoleic acid (18:2, n-6) and arachidonic acid (20:4, n-6) in isolated liver cells from female rats than in those from males. alpha-Bromopalmitate decreased triacylglycerol synthesis with a concomitant accumulation of fatty acid in diacylglycerol, indicating that the acylation of diacylglycerol is affected by alpha-bromopalmitate.

D,L-alpha-Fluoropalmitic acid inhibits sphingosine base formation and accumulates in membrane lipids of cultured mammalian cells

D,L-alpha-Fluoropalmitic acid was synthesized by tosylation of methyl-D,L-alpha-hydroxypalmitate, and displacement of the tosylated function by tetrabutylammonium fluoride in acetonitrile. Uptake and utilization of the compound by cultured Balb/c 3T3 cells were studied after presentation of the fluoro fatty acid analogue complexed with bovine serum albumin. A concentration of 0.28 mM had very little effect on cell growth over several days of incubation, and cell morphology was unchanged. Chromatographic and mass spectrometric analyses at 6 and 12 h of incubation showed that D,L-alpha-fluoropalmitic acid was taken up by the cells and incorporated without modification as a fatty acyl moiety into select lipids. Significant levels of the compound were found at 12 h in phosphatidylcholine (1.6%) and sphingomyelin (0.6%) fatty acids, but not in those of other phospholipids or neutral lipids. D,L-alpha-Fluoropalmitic acid represented a significant percentage of the fatty acids of neutral glycosphingolipids (1.4%) and ceramides (0.8%) by 12 h. The fluoro fatty acid was not incorporated into long-chain sphingolipid bases, and mass spectrometry failed to reveal additional carbon-2 fluorine-substituted compounds in cellular lipids. Cellular levels of triacylglycerols and phosphatidylcholine remained essentially unchanged, or were slightly increased, while amounts of ceramide and gangliosides were decreased. Comparison of labeled palmitate incorporation into sphingolipid bases and fatty acids of sphingomyelin suggested inhibition of sphingosine synthesis by the fluoro fatty sphingomyelin suggested inhibition of sphingosine synthesis by the fluoro fatty acid. D,L-alpha-Fluoropalmitic acid inhibited the formation of palmitoyl-CoA by Balb/c 3T3 long-chain acyl-CoA synthetase in vitro. The results support involvement of CoA thiol ester-independent steps in modification of membrane lipids.

Location of double bonds in two unsaturated forms of phytanic acid from Refsum disease as determined by mass spectrometry

A monounsaturated and a triunsaturated form of phytanic acid (3,7,11,15-tetramethylhexacosanoate) were isolated from plasma lipids of a patient with Refsum disease. Both were converted to their methyl esters, oxidized to polyhydroxy acids by treatment with OsO4 and converted to their vicinal trimethylsilyl ethers. These derivatives were analyzed by gas chromatography-mass spectrometry using both electron impact ionization (at 21 and 70 eV) and chemical ionization conditions to obtain clear evidence to establish the structure of the monounsaturated form of phytanic acid as 3,7,11,15-tetramethylhexadec-15-monoenoic acid and that of the triunsaturated form of phytanic acid as 3,7,11,15-tetramethylhexadec-6,10,14-trienoic acid. The possible metabolic and dietary sources for these novel fatty acids are discussed.

On the capacity of the beta-oxidation of palmitate and palmitoyl-esters in rat liver mitochondria

The beta-oxidation of palmitate, palmitoyl-CoA and palmitoyl-L-carnitine proceeded at a high rate in isolated rat liver mitochondria. At high concentrations (100 nmol/mg protein) the oxidation of palmitate and palmitoyl-CoA was only partly carnitine dependent. All substrates were most rapidly oxidized in the presence of oxaloacetate and state 3 conditions. Succinate inhibited beta-oxidation especially in state 4 conditions. beta-Oxidation was faster in hypotonic than in isotonic medium both in state 3 and state 4 conditions. Hypertonicity inhibited beta-oxidation. The initial formation of palmitoyl-CoA from palmitate, CoA and ATP was faster than the oxidation of palmitate under identical conditions. The presence of bovine serum albumin inhibited the beta-oxidation, especially with palmitoyl-CoA or free palmitate as the substrates. Mitochondria contain a palmitoyl-CoA hydrolase which may influence the available intramitochondrial palmitoyl-CoA. The present results demonstrate no single rate limiting step in the beta-oxidation in vitro. Both the NADH/NAD ratio, competition for the respiratory chain, the level of ADP, binding of palmitoyl-CoA to extramitochondrial protein, and possibly intramitochondrial hydrolysis of palmitoyl-CoA all seem to influence the rate of beta-oxidation in vitro. It is suggested that in vivo the most important factor is the availability of acyl-CoA to the outer carnitine palmitoyl-transferase of the mitochondria.

Uptake of labeled palmitate by the intact liver: role of intracellular binding sites

The multiple-indicator dilution technique was utilized to examine the hepatic uptake of albumin-bound labeled palmitate from the portal vein blood of the pentobarbital-anesthetized dog, in a fasted state and after infusion of a variety of compounds that were expected to bind to Z protein, the cellular cytosolic protein binding free fatty acids, and their acyl-CoA derivatives. Analysis of the data indicates that after infusion of alpha-bromopalmitate, 16-bromo-9-hexadecenoate, and sulfobromophthalein sodium (which also bind to albumin), the palmitate label influx, efflux, and metabolic sequestration (removal of label from the pool of free fatty acids able to leave the cell) all increase and that, after infusion of flavaspidic acid, label efflux and metabolic sequestration increase. In vitro competitive binding studies carried out on the cellular cytosol indicat that the basis for the increase in efflux and metabolic sequestration is displacement of labeled palmitate from high affinity sites on the intracellular Z protein (which are presumably in equilibrium with and may be taken to be representative of other intracellular binding sites). These studies also suggest that increased uptake is due to similar displacement from high affinity sites on serum albumin.

A direct radioimmunoassay for human renin substrate and identification of multiple substrate types in plasma

Plasma renin substrate, a widely measured parameter of the renin reaction, is quantitated indirectly by the measurement of liberated angiotensin I upon exhaustive incubation of plasma with added renin. To overcome methodological problems of this assay system, we have developed a direct radioimmunoassay for this plasma protein using renin substrate purified from pooled plasma of normotensive subjects as the antigen. Comparison of substrate quantitated by the two assay systems (direct and indirect) indicates a 1:1 correlation with the exception of certain subjects with elevated substrate levels induced by estrogen therapy. To study the possibility of multiple substrate forms, we have made a comparison of substrate quantitated by both radioimmunoassays in conjunction with electrophoresis of plasma on polyacrylamide gel. One major form of substrate with a retardation factor (Rf) = 0.60 was found in normotensive and essential hypertensive subjects which gave a 1:1 correspondence on quantitation by the two methods. In contrast, six of 16 women on oral contraceptives demonstrated three forms of substrate (Rf = 0.16, 0.35, and 0.60) on electrophoresis. Substrate with Rf = 0.16 and 0.35 did not cross-react with the antiserum prepared against substrate from normotensive subjects, implying structural differences in these proteins.

Fatty acid binding protein. Role in esterification of absorbed long chain fatty acid in rat intestine

Fatty acid binding protein (FABP) is a protein of 12,000 mol wt found in cytosol of intestinal mucosa and other tissues, which exhibits high affinity for long chain fatty acids. It has been suggested that FABP (which may comprise a group of closely related proteins of 12,000 mol wt) participates in cellular fatty acid transport and metabolism. Although earlier findings were consistent with this concept, the present studies were designed to examine its physiological function more directly. Everted jejunal sacs were incubated in mixed fatty acid-monoglyceride-bile acid micelles, in the presence or absence of equimolar concentrations of either of two compounds which inhibit oleate binding to FABP:flavaspidic acid-N-methyl-glucaminate and alpha-bromopalmitate. Oleate uptake, mucosal morphology, and oxidation of [14C]acetate remained unaffected by these agents, but oleate incorporation into triglyceride was inhibited by 62-64% after 4 min. The inhibition by flavaspidic acid was reversible with higher oleate concentrations. The effect of these compounds on enzymes of triglyceride biosynthesis was examined in intestinal microsomes. Neither flavaspidic acid nor alpha-bromopalmitate inhibited acyl CoA:monoglyceride acyl-transferase. Fatty acid:coenzyme A ligase activity was significantly enhanced in the presence of partially purified FABP, probably reflecting a physical effect on the fatty acid substrate or on the formation of the enzyme-substrate complex. Activity of the enzyme in the presence of 0.1 mM oleate was only modestly inhibited by equimolar flavaspidic acid and alpha-bromopalmitate, and this effect was blunted or prevented by FABP. We conclude that in everted gut sacs, inhibition of triglyceride synthesis by flavaspidic acid and alpha-bromopalmitate could not be explained as an effect on fatty acid uptake or on esterifying enzymes in the endoplasmic reticulum but rather can be interpreted as reflecting inhibition of fatty acid binding to FABP. These findings lend further support to the concept that FABP participates in cellular fatty acid transport and metabolism. It is also possible that FABP, by effecting an intracellular compartmentalization of fatty acids and acyl CoA, may play a broader role in cellular lipid metabolism.

Erucic acid metabolism by rat heart preparations

Rat heart preparations metabolized erucic acid at much slower rates than palmitic acid. This applied for activation reaction, for the conversion of acyl-CoA to acylcarnitine, and for the utilization of acyl group for oxidation. As compared to palmityl-CoA, erucyl-CoA exhibited a lower affinity for carnitine palmityltransferase (EC 2.3.1.23), the respective apparent Michaelis constants were 43 and 83 muM. Presence of erucyl-CoA or erucyl-carnitine slowed the mitochondrial oxidation of palmityl groups apparently because of the slower oxidation of erucyl groups. However, presence of erucate did not inhibit the activation of palmitate. Heart mitochondria obtained from rats fed rapeseed oil (50 cal %) or corn oil diet for 3 days showed similar abilities for the coupled oxidation of various substrates and similar carnitine palmityltransferase activities. Thus, a suggestion of gross mitochondrial malfunction following rapeseed oil consumption was not confirmed.