Carnitine Acetyltransferase Activity Research Articles

Effects of substrate binding and pH on the secondary structure of carnitine acetyltransferase

Carnitine acetyltransferase (CAT) exists as a monomer in solution as demonstrated by dynamic light scattering measurements. Under these conditions, interactions between CAT and its substrates, l-carnitine and acetyl-CoA, were studied by circular dichroism (CD) and fluorescence spectroscopy over a wide range of substrate concentrations. CD data indicated that the binding of l-carnitine and acetyl-CoA caused changes in the secondary structure of the protein. Quenching of the intrinsic protein fluorescence upon binding of either substrate corroborated these findings. Analysis of the binding data suggests that binding of both substrates to CAT is specific and saturable, and that there is a single binding site (or multiple identical and independent binding sites) on CAT for each substrate. Estimated l-carnitine/CAT dissociation constants were 506 ± 58 μM and236 ± 27 μM in the absence or presence of acetyl-CoA,.respectively. The dissociation constant for acetyl-CoA/CAT was estimated at 19 ± 7 μM. The effect of pH on the secondary structure of the protein was determined in order to investigate the structural cause for the pH-dependent enzymatic activity of CAT. Loss of α-helices and a reduction of thermal stability in CAT was detected at both acidic and basic pH. Thus, the reduced catalytic activity of CAT at acidic or basic pH may be due to pH-induced protein unfolding.

Carnitine, carnitine acetyltransferase, and glutathione in Alzheimer brain

Glutathione and "total" carnitine (i.e., free carnitine plus acid-soluble carnitine esters) were measured in an affected (superior frontal gyrus; SFG) and unaffected (cerebellum: CBL) region of Alzheimer disease (AD) and control brains. Average glutathione content in AD SFG (n = 13) and AD CBL (n = 7) (7.9 +/- 2.1 and 11.9 +/- 4.0 nmol/mg protein, respectively (mean +/- S.D.)) was similar to that in control SFG (n = 13) and CBL (n = 6) (7.7 +/- 2.0 and 11.6 +/- 2.6 nmol/mg protein, respectively). However, glutathione increased significantly with age in AD brain (p = 0.003) but not in control brain. Average total carnitine in AD SFG (84 +/- 47 pmol/mg protein; n = 10) and AD CBL (108 +/- 86 pmol/mg protein; n = 7) was not significantly different from that in the corresponding regions of control brain (148 +/- 97 (n = 10) and 144 +/- 107 (n = 6) pmol/mg protein, respectively). However, a significant decline of total carnitine with age in both regions was noted for AD brain, but not for control brain. Carnitine acetyltransferase activity in the AD SFG (n = 13) was not significantly different from that of control SFG (n = 13) (1.83 +/- 1.05 and 2.04 +/- 0.82 nmol/min/mg protein, respectively). However, carnitine acetyltransferase activity of AD CBL (n = 7) was significantly lower than that of control CBL (n = 6) (1.33 +/- 0.88 versus 2.26 +/- 0.66 nmol/min/mg protein; p = 0.05).

Increased pivaloylcarnitine in the liver of the sodium pivalate treated rat exposed to clofibrate

Clofibrate, a potent peroxisomal proliferator, increased the concentration of pivaloylcarnitine (nmol/g) in rat liver (mean ± S.D.) from 11 ± 1 (controls) to 213 ± 39 (clofibrate), in heart from 348 ± 107 to 521 ± 41 and in brown adipose tissue from 185 ± 52 to 184 ± 39 after administration of sodium pivalate. Clofibrate feeding increased the activity of carnitine acetyltransferase (U/mg) in liver (mean ± S.D.) from 0.02 ± 0.00 to 0.41 ± 0.07 and decreased the triacylglycerol concentration (mg/g liver, mean ± S.D.) from 33.53 ± 4.53 to 11.03 ± 0.71.

Thyroid hormones regulate development of energy metabolism enzymes in rat proximal convoluted tubule

Ketone bodies represent preferred energy substrates in the adult rat proximal tubule. They are abundant in the plasma of suckling rats and might represent an important oxidative substrate for the immature proximal tubule. The postnatal development of two enzymes involved in ketone body oxidation pathway, 3-ketoacid-CoA transferase and acetoacetyl-CoA thiolase, and of citrate synthase and carnitine acetyltransferase was studied in microdissected rat proximal convoluted tubule (PCT) at 1, 8, 16, and 21 days after birth. The enzyme levels in PCT of juxtamedullary and subcapsular nephrons were compared at 8, 16, and 21 days. A role of thyroid hormones in regulating the development of these enzymes was investigated by studying 8- and 21-day-old pups made hypothyroid by propylthiouracyl (PTU) treatment, as well as 21-day hyperthyroid rats. PTU treatment had no effect on enzyme activities on day 8. In contrast, the activity of all mitochondrial enzymes, except acetoacetyl-CoA thiolase, was significantly decreased in 21-day-old hypothyroid pups. In hypothyroid animals, the normal development of 3-ketoacid-CoA transferase, citrate synthase, and carnitine acetyltransferase could be restored after treatment by triiodothyronine (T3). In addition, one single injection of T3 to 8-day-old control pups induced a precocious rise in the activity of 3-ketoacid-CoA transferase, citrate synthase, and carnitine acetyltransferase in juxtamedullary PCT and in the activity of citrate synthase and carnitine acetyltransferase in subcapsular PCT. Altogether, these results point out the importance of the postnatal physiological rise in T3 in triggering the development of some mitochondrial oxidative enzymes in the PCT.

Propionate modifies lipid biosynthesis in rat peritoneal macrophages

1. 1. This study examines the effect of propionate, normally produced in the gut, on lipid metabolism of resident macrophage. This cell is very abundant in the epithelial lining of the gut. 2. 2. The activity of propionyl-CoA synthetase in macrophages was shown to be 0.39 nmol/min per mg protein, so this cell presents the ability to use propionate. Propionate at concentrations varying from 0.5 to 5 mM did not affect the activities of carnitine acetyltransferase, ATP-citrate lyase, acetoacetyl-CoA thiolase and 3-oxoacid-CoA transferase. 3. 3. Thus this short chain fatty acid did not alter the capacity for transfering acetyl-CoA from mitochondria to cytosol and for ketone bodies formation and oxidation. However, propionate (40 mM) inhibited the incorporation of [l- 14C]-palmitate into phospholipids, cholesterol, cholesterol ester and triacylglycerol and the incorporation of [3- 14C]-pyruvate into phospholipids. 4. 4. These findings suggest that fibre-rich diet by generating propionate may regulate macrophage lipid metabolism.

Hepatic microsomal induction profile of carbamic acid [[2,6-bis(1-methylethyl)phenoxy] sulfonyl]-2,6-bis(1-methylethyl) phenyl ester, monosodium salt (PD138142-15), a novel lipid regulating agent

Induction of hepatic microsomal cytochrome P450 produced by carbamic acid [[2,6-bis(1-methylethyl)phenoxy]sulfonyl]-2,6-bis(1-methylethyl) phenyl ester, monosodium salt (PD138142-15), a novel water-soluble inhibitor of acyl-CoA:cholesterol acyltransferase, was examined in male and female rats, dogs, and monkeys, and in male guinea pigs. Relative to control, PD138142-15 increased hepatic microsomal total spectral P450 in all species examined. Hepatic microsomal ethoxyresorufin- O-deethylase, pentoxyresorufin- O-dealkylase, and peroxisomal carnitine acetyltransferase activities and cyanide-insensitive β-oxidation were affected only marginally. Erythromycin- N-demethylase activity was increased (2- to 6-fold) in all three species in which it was examined (rat, dog and pig). Marked increases in immunoreactive P450 3A were noted in rats and dogs, while slight increases were seen in monkeys. Pharmacokinetic studies of PD138142-15 in rats and dogs revealed pronounced decreases (80–90%) in plasma C max, and AUC within 2 weeks of initiation of daily dosing. In spite of the marked decline in plasma drug levels, efficacy in dogs, as determined by serum cholesterol levels, was maintained for up to 6 weeks with continued dosing. Potential acid (gastric) breakdown products of PD138142-15 were examined for their hepatic cytochrome P450 induction profiles in rats and were found to differ both quantitatively and qualitatively from profiles produced by the parent compound. This suggested that induction observed in rats was due to parent PD138142-15 and not to any of the known potential acid breakdown products. The cumulative data establish that PD138142-15 is an inducer of P450 3A in rats and dogs. The results also suggest that P450 3A is induced in monkeys and pigs as well, although the data are less definitive. Decreases in plasma drug levels imply that the compound may be an autoinducer in dogs and rats. The maintenance of efficacy in spite of decreased drug levels in dogs suggests that the effects on serum cholesterol are due to a metabolite or that cholesterol lowering effects occur before the compound is metabolized by the liver.

Effect of peroxisome proliferators and inducers of xenobiotic metabolism on marker enzyme activities in cultured rat liver slices

Previous work has demonstrated that precision-cut liver slices represent a valuable in vitro system for studying the metabolism and toxicity of xenobiotics. We have investigated their use for enzyme induction studies. Liver slices were prepared from male Sprague-Dawley rats and by using a dynamic culture system could be maintained in RPMI 1640 medium for up to 72 hr. The addition of 0.02–0.5 m m concentrations of ciprofibrate, nafenopin and Wy-14,643 for 48 and 72 hr produced a concentration and time dependent induction of palmitoyl-CoA oxidation and carnitine acetyltransferase activities. Ultrastructural examination of liver slices revealed an increase in the number of peroxisomes. Liver slices were also cultured with 0.2–5 m m phenobarbitone, 5–50 μ m β-naphthoflavone and 0.5–20 μg Aroclor 1254/ml and effects on the metabolism of 7-ethoxycoumarin, 7-benzoxyresorufin and 7-ethoxyresorufin determined. All three compounds produced a concentration and time dependent induction of mixed-function oxidase enzyme activities. The results of this study demonstrate that rat liver slices can be cultured for up to 72 hr and appear to retain functional viability in that they respond to some known peroxisome proliferators and inducers of xenobiotic metabolism. Cultured liver slices may thus be a useful alternative in vitro system to hepatocytes for screening compounds for effects on various enzyme activities.

Carnitine and derivatives in the central nervous system of chick embryo

1. 1. Carnitine contents and the activity of carnitine acetyltransferase in the egg, in the embryo, and in different brain areas of central nervous system in chick embryo were determined in the course of development. 2. 2. The egg showed low levels of free carnitine and acetylcarnitine. 3. 3. In the whole embryo, at first stages of development, long chain acylcarnitines and acetylcarnitine were the best represented classes of carnitines. 4. 4. In the brain regions acetylcarnitine levels, high at the first days, showed a continual decrease during development. 5. 5. The activity of carrietine acetyltransferase increased and was totally related to development.

Anaplerotic Effect of Propionyl Carnitine in Rat Heart Mitochondria

Carnitine and propionyl carnitine both increase production of 14CO2 from [1-14C]pyruvate but only the latter, in a process inhibited by malonate, increases oxygen uptake and 14CO2 evolution from [2-14C]pyruvate. Carnitine increases the rate of formation of acetyl camitine from pyruvate to a greater extent than propionyl carnitine. These effects of carnitine and propionyl carnitine are not detectable in mitochondria (e.g., rat liver) deficient in carnitine acetyl transferase activity.

Effects of humic acid‐metal complexes on hepatic carnitine palmitoyltransferase, carnitine acetyltransferase and catalase activities

AbstractA significant increase in activities of hepatic carnitine palmitoyltransferase and carnitine acetyltransferase was observed in male Balb/c mice intraperitoneally injected for 40 d with 0 125 mg/0 1 ml/d humic acid‐metal complexes. Among these complexes, the humic acid‐As complex was relatively effective, whereas humic acid‐25 metal complex was more effective, and humic acid‐26 metal complex was most effective However, humic acid or metal mixtures, or metal such as As alone, was not effective Humic acid‐metal complexes also significantly decreased hepatic catalase activity. A marked decrease of 60‐kDa polypeptide in liver cytoplasm was also observed on SDS‐polyacrylamide gel electrophoresis after the mice had been injected with the complexes. Morphological analysis of a histopathological biopsy of such treated mice revealed several changes in hepatocytes, including focal necrosis and cell infiltration, mild fatty changes, reactive nuclei, and hypertrophy Humic acid‐metal complexes affect activities of metabolic enzymes of fatty acids, and this results in accumulation of hydrogen peroxide and increase of the lipid peroxidation The products of lipid peroxidation may be responsible for liver damage and possible carcino‐genesis. Previous studies in this laboratory had shown that humic acid‐metal complex altered the coagulation system and that humic acid, per se, caused vasculopathy. Therefore, humic acid‐metal complexes may be main causal factors of not only socalled blackfoot disease, but also the liver cancer prevailing on the southwestern coast of Taiwan.

Ultrastructural localisation of carnitine acetyltransferase activity in mitochondria of rat myocardium

The acetyl CoA CoA ratio is an important regulating factor of β-oxidation in mitochondria and hence of energy production in the myocardium. Carnitine acetyltransferase provides one of the control mechanisms for this ratio during changing energy demand in the heart muscle, possibly by buffering the CoA and carnitine concentration for sustained β-oxidation. In search for a possible correlation between the activity of this enzyme and ultrastructural changes in heart mitochondria, carnitine acetyltransferase was cytochemically localised in rat myocardium, brought into different metabolic states. In this work we confirm previous observations, namely the formation of contact sites between inner and outer mitochondrial membranes upon catecholaminergic stimulation of the myocardium. It is further shown that this contact site formation might be a prerequisite for carnitine acetyltransferase to demonstrate enzymatic activity and hence control of β-oxidation in myocardial mitochondria.

Retinal Cholinergic System: Characterization of Rat Retinal Acetyltransferases Using Specific Inhibitors of Choline- and Carnitine-Acetyltransferases

Choline acetyltransferase catalyzes the synthesis of acetylcholine from choline and acetylcoenzyme A (ACoA) in both nervous and non-nervous tissues. Carnitine acetyltransferase occurs in several tissues and transfers acetyl groups from ACoA to carnitine forming acetylcarnitine and exhibits weak choline acetyltransferase activity. Several haloacetylcholines and haloacetylcarnitines were synthesized to develop selective inhibitors of choline acetyltransferase and carnitine acetyltransferase. Acetylcholine is a transmitter for some presynaptic neurons and/or amacrine cells in retina. Selective inhibitors of choline acetyltransferase and carnitine acetyltransferase were used in the evaluation of choline acetyltransferase and carnitine acetyltransferase activities in the rat retina. Choline acetyltransferase and carnitine acetyltransferase activities were assayed by transferring of [14C]acetyl group from [14C]ACoA to choline or carnitine and estimating [14C]-acetylcholine or [14C]acetylcarnitine. This study gave the following results: (a) Bromoacetylcholine (BrACh) was a selective inhibitor of purified choline acetyltransferase (I50, 2.2 microM); (b) (R)-bromoacetylcarnitine [(R)-BrACa] was more potent for inhibiting purified carnitine acetyltransferase (I50, 4 microM) than purified choline acetyltransferase (I50, 46 microM); (c) Rat retinal sonicate gave choline acetyltransferase activity of 98 +/- 6 nmol of ACh formed/mg/10 min. When the carnitine acetyltransferase was completely inhibited by (R)-BrACa, the activity for choline acetyltransferase decreased to 47 +/- 1 nmol, and this decrease was possibly due to the formation of some [14C]acetylcholine by carnitine acetyltransferase. The net retinal choline acetyltransferase activity was 51 nmol acetylcholine/mg protein/10 min; (d) Rat retinal sonicate contained carnitine acetyltransferase activity of 102 +/- 7 nmol acetylcarnitine formed/mg protein/10 min. This was not altered by inhibition of choline acetyltransferase with BrACh. This means that choline acetyltransferase did not use carnitine as a substrate. Choline acetyltransferase and carnitine acetyltransferase activities did not change after dialysis of retinal sonicates at 4 degrees C for 24 hrs. These observations suggest that BrACh and (R)-BrACa are useful for assessing the correct values for choline acetyltransferase and carnitine acetyltransferase activities in retinal tissues.

Induction of cytochrome P4504A by the peroxisome proliferator perfluoro- n-octanoic acid

The influence of a single dose of the peroxisome proliferator, perfluoro- n-octanoic acid (PFOA) on hepatic and renal mixed-function oxidase activities has been examined in rats. Peroxisome proliferation was confirmed by increases in peroxisomal palmitoyl-CoA oxidation and carnitine acetyl transferase activity, particularly in liver. The liver was also more susceptible than the kidney to PFOA-dependent induction of the 12-hydroxylation of lauric acid, suggesting induction of the CYP4A sub-family. This was further confirmed by Western blot analyses, wherein an anti-CYP4A1 antibody revealed a substantial PFOA-dependent induction of CYP4A1 in a pattern similar to that observed for the classical peroxisome proliferator, clofibrate. In addition, using a cDNA probe to CYP4A1 in Northern blot analysis, PFOA treatment resulted in a marked increase in the steady state level of CYP4A1 mRNA, again more extensively in liver than in kidney. Taken collectively, our data provide compelling evidence that PFOA, like other peroxisome proliferators, is also an inducer of the CYP4A sub-family.

The Presence of L-Carnitine in Ocular Tissues of the Rabbit

Carnitine plays an important role in the metabolism of fatty acids. Its presence is considerable in tissues that use fatty acids as an important source of energy, such as the heart and skeletal muscle. Free carnitine and acid soluble acylcarnitines are present in various tissues of the rabbit eye. The lowest concentration of carnitine was observed in the vitreous humor and the highest in the lens. The ratio, acid soluble acylcarnitine/free carnitine, was lower in the cornea, aqueous humor, vitreous humor and lens, than in iris, ciliary body and choroid-retina. The topical administration of carnitine increased both free carnitine and acetylcarnitine in cornea, and only free carnitine in aqueous humor and choroid retina. Only after intravenous administration, did the levels of free and acyl-carnitine increase in the iris and ciliary body. Neither of the two carnitine species was changed in vitreous humor. The determination of the activity of carnitine acetyltransferase in the eye showed that in the ciliary body the values of activity were three times higher than those in the iris and choroid-retina. The elevated ratio of acid soluble acylcarnitines with respect to free carnitine in iris, ciliary body, choroid-retina as well as the higher activity of carnitine acetyltransferase in the ciliary body, suggest that carnitine plays an important role in those tissues of the eye where cells of a muscular nature are present and may represent, after esterification, an important energy reserve.

The ethanol-inducible YAT1 gene from yeast encodes a presumptive mitochondrial outer carnitine acetyltransferase.

The gene YAT1 from Saccharomyces cerevisiae encodes a protein of 688 amino acids which displays significant sequence similarity to vertebrate L-carnitine acyltransferases and yeast inner mitochondrial L-carnitine acetyltransferase. Steady state levels of the respective mRNA are low during growth on glucose or galactose, derepressed on glycerol, and significantly induced when ethanol or acetate are the only carbon sources. The YAT1 promotor region confers the identical carbon source dependence also on the expression of beta-galactosidase when cloned 5' to the Escherichia coli lacZ-coding region. An antiserum directed against a beta-galactosidase/Yat1p fusion protein recognizes a protein of 78-kDa molecular mass in the mitochondrial fraction from yeast. In vitro translated Yat1p, which lacks a cleavable presequence, binds to mitochondria in a protease-sensitive location in a standard in vitro import assay. Deletion of the single copy gene in a haploid yeast strain yields no obvious phenotype with any carbon source. Carnitine acetyltransferase activities of intact mitochondria from a YAT1 deletion mutant are slightly lower than wild type, but are approximately alike in lysed mitochondria from mutant and control cells. Thus, the novel gene is nonessential and likely to code for a minor mitochondrial outer carnitine acetyltransferase.

Structure-activity relationships for induction of peroxisomal enzyme activities in primary rat hepatocyte cultures

Rat hepatocytes were cultured for 70 hr with a series of 15 chemicals (including herbicides and derivatives, hypolipidaemic agents and other compounds) and the effects on some enzyme activities were determined. All of the compounds produced concentration-related increases in the activities of peroxisomal fatty acid β-oxidation (palmitoyl-CoA oxidation), catalase, carnitine acetyltransferase and lauric acid 12-hydroxylase. Marked differences between the potencies of the compounds were observed but some correlations were obtained between the induction of palmitoyl-CoA oxidation and the other three enzyme activities measured. Quantitative structure-activity relationships (QSARs) were observed between the induction of palmitoyl-CoA oxidation and catalase activities and compound electronic structural parameters obtained by molecular orbital calculations (MINDO/3 method). In these studies both compound bulk molecular parameters and parameters of the free carboxyl group (present in all of the chemicals examined) were important in determining compound potencies. The existence of QSARs between biological activity and chemical structure for a series of peroxisome proliferators suggests that these compounds share a common mechanism of initiation of peroxisome proliferation in rodent liver. The data also demonstrate the usefulness of rat hepatocyte cultures for screening compounds for peroxisome proliferation and for investigating structure-activity relationships.

Presence of carnitine acetyltransferase in peroxisomes and in mitochondria of oleic acid-grown Saccharomyces cerevisiae

Activity of carnitine acetyltransferase was detected in glucose- and oleic acid-grown Saccharomyces cerevisiae. Oleic acid-grown cells showed a ten-fold higher activity than glucose-grown cells. Subcellular fractionation of oleic acid-grown cells showed that carnitine acetyltransferase was present in peroxisomes, mitochondria, and cytosol. The results suggested the plausible presence of an ‘acetylcarnitine shuttle’ in this yeast, as in the case of an n-alkane-assimilating yeast, Candida tropicalis.

Presence of carnitine acetyltransferase in peroxisomes and in mitochondria of oleic acid-grown Saccharomyces cerevisiae.

Activity of carnitine acetyltransferase was detected in glucose- and oleic acid-grown Saccharomyces cerevisiae. Oleic acid-grown cells showed a ten-fold higher activity than glucose-grown cells. Subcellular fractionation of oleic acid-grown cells showed that carnitine acetyltransferase was present in peroxisomes, mitochondria, and cytosol. The results suggested the plausible presence of an 'acetylcarnitine shuttle' in this yeast, as in the case of an n-alkane-assimilating yeast, Candida tropicalis.

Induction of peroxisomal β-oxidation by structural analogues of dehydroepiandrosterone in cultured rat hepatocytes: Structure-activity relationships

The structural requirements of dehydroepiandrosterone (DHEA) for the induction of peroxisomal β-oxidation were studied in cultured rat hepatocytes. The hepatocytes were incubated for 5 days with various steroids, including 3- and 17-substituted analogues and 5-hydrogenated analogues of DHEA, and the activities of peroxisomal β-oxidation and carnitine acetyltransferase were measured. Among the steroids examined, DHEA, DHEA sulfate (DHEAS), dehydroandrosterone sulfate, androstenediol 3-sulfate, epiandrosterone sulfate and androsterone sulfate significantly induced the enzymes; 4.6- to 14.2-fold for β-oxidation and 5.1- to 10.9-fold for carnitine acetyltransferase at 50 μM. All of the sulfated steroids were more effective than the corresponding unsulfated forms. DHEAS was the most potent inducer. The 3-sulfuric group was required for the marked induction of peroxisomal β-oxidation, and the 17-carbonyl group was also important. Furthermore, the relatively planar conformation of the steroidal hydrophobic backbone was crucial for inducing the enzyme. The configuration of the 3-sulfuric group (β-configuration) and the presence of a double bond at position C5 were not primary determinants for the action of DHEAS. On the other hand, the introduction of bulky substituents to position C17 or aromatization of ring A led to a loss of inducing activity. Thus, there are strict structural requirements for the DHEA induction of peroxisomal β-oxidation, suggesting the presence of a certain specific recognition site in the cell for DHEAS, which mediates the peroxisome proliferator action of DHEA.

Is Acetylcarnitine a Substrate for Fatty Acid Synthesis in Plants?

Long-chain fatty acid synthesis from [1-14C]acetylcarnitine by chloroplasts isolated from spinach (Spinacia oleracea), pea (Pisum sativum), amaranthus (Amaranthus lividus), or maize (Zea mays) occurred at less than 2% of the rate of fatty acid synthesis from [1-14C]acetate irrespective of the maturity of the leaves or whether the plastids were purified using sucrose or Percoll medium. [1-14C]-Acetylcarnitine was not significantly utilized by highly active chloroplasts rapidly prepared from pea and spinach using methods not involving density gradient centrifugation. [1-14C]Acetylcarnitine was recovered quantitatively from chloroplast incubations following 10 min in the light. Unlabeled acetyl-L-carnitine (0.4 mM) did not compete with [1-14C]acetate (0.2 mM) as a substrate for fatty acid synthesis by any of the more than 70 chloroplast preparations tested in this study. Carnitine acetyltransferase activity was not detected in any chloroplast preparation and was present in whole leaf homogenates at about 0.1% of the level of acetyl-coenzyme A synthetase activity. When supplied to detached pea shoots and detached spinach, amaranthus, and maize leaves via the transpiration stream, 1 to 4% of the [1-14C]acetylcarnitine and 47 to 57% of the [1-14C]acetate taken up was incorporated into lipids. Most (78-82%) of the [1-14C]acetylcarnitine taken up was recovered intact. It is concluded that acetylcarnitine is not a major precursor for fatty acid synthesis in plants.