Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.3.1.21 (CPT)
4,580 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interaction of gluconeogenesis and fatty acid oxidation in isolated sheep hepatocytes was studied. Addition of tetradecylglycidic acid, an inhibitor of carnitine palmitoyltransferase I (EC 2.3.1.21), to isolated hepatocytes inhibited gluconeogenesis from a mixture of pyruvate plus lactate and from propionate alone. Inhibition constants for tetradecylglycidic acid on gluconeogenesis were 4.77 +/- 1.00 microM and 7.25 +/- 1.52 microM, respectively, for pyruvate plus lactate and for propionate as gluconeogenic substrates. The inhibition constants were not different. At the highest substrate concentrations examined, gluconeogenesis from pyruvate plus lactate and from propionate in the presence of 10 microM tetradecylglycidic acid was 47.3 and 41.4% of their respective controls. Similar to previous observations with butyrate, caproate addition inhibited gluconeogenesis from propionate by isolated hepatocytes and was unable to prevent inhibition of gluconeogenesis induced by tetradecylglycidic acid. Carnitine palmitoyltransferase I activity was lower in mitochondria isolated from hepatocytes preincubated with insulin than in control hepatocytes. The data suggest 1) that maximum rates of gluconeogenesis in isolated sheep hepatocytes from either pyruvate plus lactate or from propionate as gluconeogenic substrates require beta-oxidation, 2) that intermediates common to the metabolism of butyrate and caproate may be involved in the inhibition of propionate conversion to glucose by isolated sheep hepatocytes, and 3) that carnitine palmitoyltransferase I activity in isolated sheep hepatocytes can be modulated by insulin treatment.
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PMID:Interactions between gluconeogenesis and fatty acid oxidation in isolated sheep hepatocytes. 140 66

In animal cells long chain fatty acids are transferred into the mitochondria for oxidation as acylcarnitines. Carnitine palmitoyltransferase I in the outer membrane, and carnitine translocase plus carnitine palmitoyltransferase II in the inner membrane catalyse the transfer. Carnitine palmitoyltransferase I is inhibited by malonyl-CoA, an intermediate in fatty acid synthesis. In the liver of fasted, diabetic, or thyreotoxic animals this enzyme shows increased activity and less inhibition by malonyl-CoA. Peroxisomes also contain carnitine acyltransferases and a beta-oxidation enzyme system. This system is particularly active in the shortening of very long chain fatty acids. The carnitine acyltransferases of the peroxisomes presumably are active in the transfer of the shortened acyl-CoAs and the acetyl-CoA to the mitochondria for complete oxidation. The carnitine acyltransferases of the mitochondria can catalyse the formation of propionylcarnitine and branched chain acylcarnitines from branched chain amino acids, and methylthiopropionylcarnitine from methionine. Their formation may represent a "security valve" preventing acyl-CoA accumulation in the mitochondria. The liver, which normally releases carnitine for other tissues, releases the branched chain acylcarnitines even more easily. This may be important for the development of secondary carnitine deficiency in some inborn errors of metabolism which are accompanied by the accumulation of acyl-CoAs in the tissue.
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PMID:The role of carnitine in intracellular metabolism. 219 93

The effects of prolonged ethanol feeding on both carnitine palmitoyltransferase I activity and enzyme sensitivity to inhibition by malonyl-CoA were studied in rat liver, heart, skeletal muscle and kidney cortex mitochondria. Heart and skeletal muscle enzymes showed the highest specific activity and sensitivity to malonyl-CoA. Carnitine palmitoyltransferase I in extrahepatic tissues showed no changes on ethanol feeding. Only the liver enzyme activity was altered after long term ethanol administration, by suffering a progressive decrease in activity and a parallel increase in sensitivity to malonyl-CoA. These alterations reversed after 10 days of ethanol withdrawal. These results are discussed in relation to the control of carnitine palmitoyltransferase I and the effects of ethanol on fatty acid metabolism.
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PMID:Ethanol feeding to rats reversibly decreases hepatic carnitine palmitoyltransferase activity and increases enzyme sensitivity to malonyl-CoA. 342 84

Carnitine palmitoyltransferase I in rat liver mitochondria preincubated with malonyl-CoA was more sensitive to inhibition by malonyl-CoA than was the enzyme in mitochondria preincubated in the absence of malonyl-CoA. For carnitine palmitoyltransferase I in mitochondria from starved animals this increase also resulted in the enzyme becoming significantly more sensitive than that in mitochondria assayed immediately after their isolation. Concentrations of malonyl-CoA that induced half the maximal degree of sensitization observed were 1-3 microM.
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PMID:Increased sensitivity of carnitine palmitoyltransferase I activity to malonyl-CoA inhibition after preincubation of intact rat liver mitochondria with micromolar concentrations of malonyl-CoA in vitro. 687 Aug 13

Long-chain fatty acids are the primary source of energy production in the heart. Carnitine palmitoyltransferase I (CPT-I) catalyzes the first reaction in the transport of long-chain fatty acids from the cytoplasm to the mitochondrion, a rate-limiting step in beta-oxidation. In this study, we report the functional expression of the human heart/skeletal muscle isoform of CPT-I (M-CPT-I) in the yeast Pichia pastoris. Screening of a human heart cDNA library with cDNA fragments encoding the rat heart M-CPT-I resulted in the isolation of a single full-length human heart M-CPT-I cDNA clone. The clone has an open reading frame of 2316 bp with a 5' untranslated region of 38 bp and a 256-bp 3' untranslated region with the poly(A)+ addition sequence AATAAA. The predicted protein has 772 amino acids and a molecular mass of 88 kDa. Northern blot analysis of mRNAs from different human tissues using the human M-CPT-I cDNA as a probe revealed an abundant transcript of approximately 3.1 kb that was only present in human heart and skeletal muscle tissue. Expression of the human M-CPT-I cDNA in P. pastoris, a yeast with no endogenous CPT activity, produced an 80-kDa protein that was located in the mitochondria. Isolated mitochondria from the M-CPT-I expression strain exhibited a malonyl-coenzyme A (CoA)-sensitive CPT activity that was detergent labile. The I50 for malonyl-CoA inhibition of the yeast-expressed M-CPT-I was 69 nM, and the Kms for carnitine and palmitoyl-CoA were 666 and 42 microM, respectively. The I50 for malonyl-CoA inhibition of the heart enzyme is 30 times lower than that of the yeast-expressed liver CPT-I, and the Km for carnitine is more than 20 times higher than that of the liver CPT-I. This is the first report of the expression of a heart CPT-I in a system devoid of endogenous CPT activity and the functional characterization of a human heart M-CPT-I in the absence of the liver isoform and CPT-II.
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PMID:Functional studies of yeast-expressed human heart muscle carnitine palmitoyltransferase I. 934 64

Carnitine palmitoyltransferase I (CPT-I) is a key enzyme involved in the regulation of fatty acid oxidation. CPT-IA and CPT-IB are isoforms of carnitine palmitoyltransferase I, of which CPT-IA is expressed in liver, kidney, fibroblasts, and heart and CPT-IB is expressed in skeletal muscle, heart, brown and white adipocytes, and testes. Although the genomic DNA sequence of human CPT-IB is available, the transcription start site and upstream regulatory sequences are not known. For rat CPT-IB, only the cDNA sequence has been published. We have cloned the entire rat CPT-IB gene from a Lambda fix II rat kidney genomic library. The genomic structure contains 19 exons, with the transcription start site for CPT-IB located in a short first exon, which is a 13-bp extension to the previously published cDNA 5' sequence. The coding sequence is identical with the rat muscle cDNA. The rat CPT-IB gene contains 18 introns and 19 exons, the latter 18 exons showing 85% homology to the human CPT-IB cDNA. CPT-IB maps to rat chromosome 7 at band q34. A putative promoter region was identified to within 391 bp of the transcription start site. The muscle specificity of the 5' flanking region was verified by comparison of luciferase expression to that of beta-galactosidase in cardiac myocytes and in HepG2 cells.
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PMID:Genomic DNA sequence, promoter expression, and chromosomal mapping of rat muscle carnitine palmitoyltransferase I. 954 36

Carnitine palmitoyltransferase I (CPT-I) catalyses the rate-determining step in mitochondrial fatty acid beta-oxidation. The enzyme has two cognate structural genes that are preferentially expressed in liver (alpha) or fat and muscle (beta). We hypothesized the existence of additional isoforms in heart to account for unique kinetic characteristics of enzyme activity in this tissue. Hybridization and PCR screening of a human cardiac cDNA library revealed the expression of two novel CPT-I isoforms generated by alternative splicing of the CPT-Ibeta transcript, in addition to the beta and alpha cDNA species previously described. Ribonuclease protection and reverse transcriptase-mediated PCR assays confirmed the presence of mRNA species of each splicing variant in heart, skeletal muscle and liver, with differing relative concentrations in the tissues. The novel splicing variants omit exons or utilize a cryptic splice donor site within an exon. Deduced polypeptide sequences of the novel enzymes include omissions in the region of putative membrane-spanning and malonyl-CoA regulatory domains compared with the previously described CPT-Is, implying that the encoded enzymes will exhibit unique features with respect to outer mitochondrial membrane topology and response to physiological and pharmacological inhibitors.
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PMID:Expression of novel isoforms of carnitine palmitoyltransferase I (CPT-1) generated by alternative splicing of the CPT-ibeta gene. 969 24

Carnitine palmitoyltransferase I (CPT-I) catalyzes the rate-determining step in mitochondrial fatty acid beta-oxidation. The enzyme has two cognate structural genes (alpha and beta) that are differentially expressed in tissues. We show multiple mature mRNAs in rat heart derived from alternative splicing of CPT-Ibeta transcripts. Two novel messages are deleted for regions of the previously described mRNA that encode membrane-spanning and regulatory domains, suggesting that the cognate isozymes will exhibit unique kinetic characteristics.
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PMID:Rat carnitine palmitoyltransferase Ibeta mRNA splicing isoforms. 971 90

Carnitine palmitoyltransferase I (CPT-I) catalyzes the rate-determining step in mitochondrial fatty acid beta-oxidation. CPT-I has two structural genes (alpha and beta) that are differentially expressed among tissues. Our CPT-Ibeta isolates from a human cardiac cDNA library contained two different extreme 5'-sequences derived from short alternative first untranslated exons that utilize a common splice acceptor site in exon 2. Primer extension identified single dominant start sites for each transcript, and ribonuclease protection assays showed the presence of one 5'-exon in liver, muscle, and heart mRNAs, indicating that the cognate promoter U (upstream/ubiquitous) is active in each of these tissues. By contrast, mRNAs containing the alternative 5'-exon were present only in muscle and heart, indicating a muscle-specific promoter M (muscle). CPT-Ibeta mRNA levels increased markedly in tissues of fasted rats, when circulating free fatty acid concentrations are elevated. Using CPT-Ibeta promoter/reporter transient transfection of murine C2C12 myotubes and HepG2 hepatocytes, fatty acids were found to increase promoter activity in a peroxisome proliferator-activated receptor alpha (PPARalpha)-dependent fashion. A promoter fatty acid response element (FARE) was mapped, mutation of which ablated fatty acid-mediated production of both transcripts. PPARalpha/retinoid X receptor alpha formed specific complexes with oligonucleotides containing the FARE, and anti-PPARalpha antibody shifted nuclear protein-DNA complexes, confirming the role of this factor in regulating the expression of this critical metabolic enzyme gene. The constitutive repressor chicken ovalbumin upstream promoter transcription factor competitively binds at the FARE and modulates fatty acid induction of the promoters.
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PMID:Co-regulation of tissue-specific alternative human carnitine palmitoyltransferase Ibeta gene promoters by fatty acid enzyme substrate. 983 40

Carnitine palmitoyltransferase I (CPT I) is a key enzyme in the regulation of beta-oxidation. The topology of this enzyme has been difficult to elucidate by biochemical methods. We studied the topology of a fusion protein of muscle-type CPT I (M-CPT I) and green fluorescent protein (GFP) by microscopical means. To validate the use of the fusion protein, designated CPT I-GFP, we checked whether the main characteristics of native CPT I were retained. CPT I-GFP was expressed in HeLa cells after stable transfection. Confocal laser scanning microscopy in living cells revealed an extranuclear punctate distribution of CPT I-GFP, which coincided with a mitochondrial fluorescent marker. Immunogold electron microscopy localized CPT I-GFP almost exclusively to the mitochondrial periphery and showed that the C-terminus of CPT I must be on the cytosolic face of the mitochondrial outer membrane. Western analysis showed a protein that was 6 kDa smaller than predicted, which is consistent with previous results for the native M-CPT I. Mitochondria from CPT I-GFP-expressing cells showed an increased CPT activity that was inhibited by malonyl-CoA and was lost on solubilization with Triton X-100. We conclude that CPT I-GFP adopts the same topology as native CPT I and that its C-terminus is located on the cytosolic face of the mitochondrial outer membrane. The evidence supports a recently proposed model for the domain structure of CPT I based on biochemical evidence.
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PMID:Cytological evidence that the C-terminus of carnitine palmitoyltransferase I is on the cytosolic face of the mitochondrial outer membrane. 1041 44


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