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)

beta-Oxidation of long-chain fatty acids increases many-fold in atherosclerotic aortas; this may be due to an increase in the activity of the mitochondrial enzyme hexadecanoyl-CoA: carnitine O-hexadecanoyltransferase EC 2.3.1.23 (trivial name: carnitine palmitoyltransferase, CPT). To investigate this possibility, an assay for arterial CPT was developed and used to measure CPT activity in mitochondrial fractions isolated from aortas of rabbits fed high-fat (HF) or high-fat plus cholesterol (HFC) supplemented diets. The arterial CPT assay was linear with respect to mitochondrial protein between 0.03 and 0.30 mg and assay time between 3 and 12 min. Maximum CPT activity was observed at concentrations of palmitoyl-CoA between 5 and 25 micron, higher concentrations of palmitoyl-CoA inhibited CPT activity. CPT activity was measured in mitochondrial fractions isolated from aortas of rabbits fed the HFC-supplemented diet for up to 48 days. No visible lesions were observed in aortas of rabbits fed HFC-diet for 3,9, or 21 days, however, by 48 days atheromatous lesions covered in excess of 60% of the intimal surface of the aorta. No lesions were visually observed in aortas of rabbits receiving the HF-diet. Despite the development of gross atherosclerotic lesions, there were no changes in CPT activity observed that could account for a dramatic increase in fatty acid oxidation. It is concluded that the increase in beta-oxidation of long-chain fatty acids in atherosclerosis is not attributable to an increase in CPT activity.
Atherosclerosis 1979 Sep
PMID:Carnitine palmitoyltransferase activity in mitochondrial fractions isolated from aortas of rabbits fed cholesterol-supplemented diets. 49 40

1. The activities of long-chain acyl-CoA synthetase (acid: CoA ligase (AMP-forming), EC 6.2.1.3) and the "outer" carnitine long-chain acyltransferase (palmitoyl-CoA: L-carnitine O-palmitoyltransferase, EC 2.3.1.21) have been estimated in intact brown adipose tissue mitochondria. The assay of both enzymes is based on a coupled reaction in which the intramitochondrial (matrix) CoASH is the final acyl acceptor and the oxidation-reduction state of the flavoproteins in the acyl-CoA dehydrogens pathway is used to determine the intramitochondrial level of acyl-CoA. 2. Using endogenous fatty acids as the substrate, the progress curve of acyl-CoA synthetase activity was in most mitochondrial preparations linear within the first 30 s. When initial rates were measured, the Km value for CoASH (2.4 micron) was lower than previously determined for the acyl-CoA synthetase in brown adipose tissue mitochondria as well as in mitochondria of other tissues. The pH activity curve indicates that the unprotonated form of the fatty acids represents the substrate of acyl-CoA synthetase, i.e. similar to the effect of pH on the binding of fatty acids to bovine serum albumin. 3. Experimental evidence is presented that at temperatures higher than the transition temperature of the acyl-CoA synthetase (i.e. Tt = 19 degrees C), this enzymic reaction is rate-limiting in the sequence of coupled reactions leading to beta-oxidation in the mitochondrial matrix. 4. The initial rate of the long-chain acyl-COA synthetase reaction was estimated to v = 119 +/- 16 nmol . min-1 . mg-1 protein (mean +/- S.D., n = 5) at an optimal concentration of palmitate which exceeds that of rat heart mitochondria by a factor of 10.
Biochim Biophys Acta 1978 Sep 28
PMID:Long-chain acyl-CoA synthetase and "outer" carnitine long-chain acyltransferase activities of intact brown adipose tissue mitochondria. 69 44

1. Enzyme activities (units/g wet wt.) were determined in the caput and cauda epididymidis and in epididymal spermatozoa of the rat. 2. The activity of most enzymes in the cauda was between 50 and 100% of that in the caput, except that ATP citrate lyase was barely detectable in the cauda. 3. Spermatozoa, unlike epididymal tissue, contained sorbitol dehydrogenase but lacked ATP citrate lyase. NADP+-malate dehydrogenase, mitochondrial glycerol 3-phosphate dehydrogenase, succinate dehydrogenase, carnitine acetyltransferase and citrate synthase were 5 to 400 times as active in spermatozoa as in epididymal tissue. 4. 2-Oxoglutarate dehydrogenase was the least active member of the tricarboxylic acid cycle in all tissues and most closely matched the measured flux through the cycle. 5. The concentrations of hydroxyacyl-CoA dehydrogenase and carnitine palmitoyltransferase were equivalent to the more active enzymes of the tricarboxylic acid cycle, indicating the capacity for extensive lipid oxidation, and the presence of 3-hydroxybutyrate dehydrogenase suggests that these tissues can also oxidize ketone bodies. 6. Transfer of reducing equivalents from cytoplasm to mitochondrion is unlikely to occur by means of the glycerol phosphate cycle because mitochondrial glycerol 3-phosphate dehydrogenase is relatively inactive in epididymal tissue, whereas the cytoplasmic enzyme has little activity in spermatozoa, but transfer may be accomplished by the malate-aspartate shuttle. 7. Transfer of acetyl units from mitochondrion to cytoplasm could be effected by the pyruvate-malate cycle in the caput of androgen-maintained rats, but not in the other tissues because of the low activity of ATP citrate lyase. Acetyl unit transfer could take place via acetylcarnitine, mediated by carnitine acetyltransferase. 8. Castration resulted in a decrease in the concentration of nearly all enzymes, although subsequent administration of testosterone restored concentrations to values similar to those in animals maintained by endogenous androgen. The extent to which enzyme concentration was changed by an alteration in androgen status was highly variable, but was most marked in the case of pyruvate carboxylase.
Biochem J 1978 Sep 15
PMID:Activity and androgenic control of enzymes associated with the tricarboxylic acid cycle, lipid oxidation and mitochondrial shuttles in the epididymis and epididymal spermatozoa of the rat. 72 83

Isolated rat atria in hypoxia released lactate into the bathing medium and underwent a decline of the contraction frequency which, in some cases led to a complete cessation of the pacemaker activity. A pronounced fall in the peak developed tension and a rise in the resting tension also appeared. The atria from 24 h fasted rats, which oxidize faster their reserve lipids than those from fed rats, exhibited greater functional disturbances during hypoxia, a lower lactate output and a smaller recovery of peak tension upon reoxygenation. Methyl palmoxirate, which is a selective inhibitor of carnitine palmitoyltransferase I, attenuated the decline of the beating rate and the rise of the resting tension in both groups of rats and the incidence of atrial arrest in the fasted rat group. The fall in the peak tension, lactate output and recovery upon reoxygenation were not altered by the inhibitor. These data indicate that methyl palmoxirate alleviates some of the hypoxic functional derangements. Hence, it may be inferred that inhibiting the oxidation of the fatty acid derived from the endogenous triacylglycerol is beneficial during oxygen-limited conditions and that these effects could not be ascribed to changes in the glycolytic flux.
Rev Esp Fisiol 1992 Sep
PMID:Effects of methyl palmoxirate on hypoxic rat atria. 130 33

Hepatocytes respond to stimulation by glycogenolytic agonists acting via phosphoinositide (PI) breakdown through oscillations of the free cytosolic concentration of Ca2+ ([Ca2+]cyt.). Since the second-messenger repertoire of hepatocytes includes many other factors besides Ca2+, we investigated to what degree the regulation of [Ca2+]cyt. oscillations is integrated into these other signalling systems. [Ca2+]cyt. was recorded in single rat hepatocytes by using the Ca(2+)-indicator fura-2. Parallel stimulation with phenylephrine (an alpha 1-adrenergic agonist of PI breakdown) and glucagon resulted in a synergistic stimulation of [Ca2+]cyt. oscillations. Direct activation of the cyclic-AMP-dependent pathway with several stimuli (forskolin, 8-bromo cyclic AMP, 8-CPT cyclic AMP) mimicked the response to glucagon. In contrast, [Ca2+]cyt. oscillations induced by various combinations of these agonists could be antagonized by the glycogenic hormone insulin. As one of the options in the insulin-signalling network, we tested a diacylglycerol activator of protein kinase C, DiC8. It also acted as an inhibitor of [Ca2+]cyt. oscillations. We investigated how these observations could be reconciled with our previously introduced model of [Ca2+]cyt. oscillations in hepatocytes [Somogyi and Stucki (1991) J. Biol. Chem. 266, 11068-11077]. First of all, the effect of calmodulin inhibitors (calmidazolium and CGS 9343 B), acting at the core of our model on the feedback of Ca2+ on Ins(1,4,5)P3-induced Ca2+ release, was not altered by the new modulators. In addition, all agonists and antagonists could be used interchangeably in combination and introduced no significant change in the oscillatory pattern or spike shape. Since the response was solely limited to frequency modulation, over- or understimulation of the oscillatory system, there is no need to create a new oscillator or to introduce further reaction steps into the core of the model. We conclude that the regulation of [Ca2+]cyt. via the explored second-messenger pathways can be embedded into the oscillatory system as modulation of rate constants already present in this model.
Biochem J 1992 Sep 15
PMID:Modulation of cytosolic-[Ca2+] oscillations in hepatocytes results from cross-talk among second messengers. The synergism between the alpha 1-adrenergic response, glucagon and cyclic AMP, and their antagonism by insulin and diacylglycerol manifest themselves in the control of the cytosolic-[Ca2+] oscillations. 132 20

The regulation of heart carnitine palmitoyltransferase was studied during the transition to the fasting state. Using decanoyl-CoA or palmitoyl-CoA as substrates, we found no differences in carnitine palmitoyltransferase activity or in its sensitivity to inhibition by malonyl-CoA between fed and fasted states. No cooperativity was seen with either substrate, and the malonyl-CoA-induced shift to sigmoid kinetics normally observed with liver mitochondria was not obvious with heart mitochondria. Analysis of malonyl-CoA inhibition data revealed that mitochondria from rat heart exhibited incomplete maximum inhibition of carnitine palmitoyltransferase (partial inhibition). Homogenization of intact liver mitochondria resulted in a similar pattern of incomplete inhibition and suggested that the malonyl-CoA-insensitive carnitine palmitoyltransferase of the inner membrane was also being assayed. Carnitine palmitoyltransferase in mitochondrial outer membranes, isolated from the heart, proved to be extremely sensitive to malonyl-CoA inhibition and had maximum inhibition values of 90-100% with either decanoyl-CoA or palmitoyl-CoA as substrates, but fasting had no effect. Fasting produced no change in the Ki for malonyl-CoA (0.10 +/- 0.04 and 0.14 +/- 0.02 microM for the fed and fasted groups, respectively). Acyl-CoA chain length specificity was C10 greater than C16 greater than C14 greater than C12 greater than C18 = C8 for carnitine palmitoyltransferase in heart mitochondrial outer membranes. It is concluded that the regulation of carnitine palmitoyltransferase of heart mitochondrial outer membranes differs from regulation of the liver enzyme in three characteristics--the heart enzyme (a) has greater sensitivity to malonyl-CoA inhibition, (b) is resistant to the effects of fasting and (c) has somewhat different acyl-CoA substrate specificity.
Biochim Biophys Acta 1992 Sep 22
PMID:Myocardial carnitine palmitoyltransferase of the mitochondrial outer membrane is not altered by fasting. 139 Aug 73

A total of 24 asymptomatic HIV-infected patients (CDC II/III) and 27 HIV-negative controls were tested for speed of reaction and for general neuropsychological functioning. Reaction time was assessed with two computerized tests with differing levels of cognitive complexity. The results show that the asymptomatic HIV-positive patients have a significantly longer mean reaction time to simple and complex stimuli (SRT p < 0.001, CPT p < 0.05), and a significantly greater standard deviation (SD) (SRT-SD p < 0.005). No significant differences were observed on any of the clinical neuropsychological tests, or in the number of false positive (FP) or non-responses to stimuli (NR) from the CPT. The results indicate that asymptomatic HIV-infected patients are slower and have a greater intra-subject variability in speed using a simple test for reaction time. The difference is less pronounced when doing a more demanding cognitive task and not significant in a test of visuo-motor coordination or on other clinical neuropsychological tests. Emotional state or cognitive strategies affecting speed/accuracy trade-off do not account for the findings.
Acta Neurol Scand 1992 Sep
PMID:Slowed reaction time in asymptomatic HIV-positive patients. 141 40

Deficiency of carnitine palmitoyltransferase II (CPTase II; palmitoyl-CoA:L-carnitine O-palmitoyltransferase, EC 2.3.1.21) is a clinically heterogeneous autosomal recessive disorder of energy metabolism. We studied the molecular basis of CPTase II deficiency in an early-onset patient presenting with hypoketotic hypoglycemia and cardiomyopathy. cDNA and genomic DNA analysis demonstrated that the patient was homozygous for a mutant CPTase II allele (termed ICV), which carried three missense mutations: a G-1203----A transition, predicting a Val-368----Ile substitution (V368I); a C-1992----T transition, predicting an Arg-631----Cys substitution (R631C); and an A-2040----G transition, predicting a Met-647----Val substitution (M647V). Genomic DNA analysis of family members showed that the mutations cosegregated with the disease in the family. However, screening of 59 healthy controls demonstrated that both the V368I and M647V mutations are sequence polymorphisms with allele frequencies of 0.5 and 0.25, respectively. By contrast, the R631C substitution was not detected in 22 normal individuals or in 12 of 14 CPTase II-deficient patients with the adult muscular form. Notably, 2 adult CPTase II-deficient patients were heterozygous for the ICV allele, thus suggesting compound heterozygosity for this and a different mutant allele. The consequences of the three mutations on enzyme activity were investigated by expressing normal and mutated CPTase II cDNAs in COS cells. The R631C substitution drastically depressed the catalytic activity of CPTase II, thus confirming that this is the crucial mutation. Interestingly, the V368I and M647V substitutions, which did not affect enzyme activity alone, exacerbated the effects of the R631C substitution. Biochemical characterization of mutant CPTase II in patient's cells showed that the mutations are associated with (i) severe reduction of Vmax (approximately 90%), (ii) normal apparent Km values, and (iii) decreased protein stability.
Proc Natl Acad Sci U S A 1992 Sep 15
PMID:Molecular characterization of inherited carnitine palmitoyltransferase II deficiency. 152 46

Although the malonyl-CoA sensitivity of peroxisomal carnitine octanoyltransferase (COT) is reportedly lost on solubilization, we show that malonyl-CoA does inhibit the purified enzyme. Assay conditions such as buffer composition, pH, acyl-CoA substrate and the presence or absence of BSA can affect the observed inhibition. When assayed in the absence of BSA, COT shows simple competitive inhibition by malonyl-CoA. The Ki value for inhibition of purified COT is high (106 microM) compared with physiological concentrations (1-6 microM) and other short-chain acyl-CoA esters inhibit COT to the same degree. However, when COT is assayed in intact peroxisomes, the Ki for malonyl-CoA is almost 20-fold lower than found with the purified enzyme, whereas inhibition by other short-chain acyl-CoA esters does not change significantly. Several features of the inhibition of peroxisomal COT, including the specificity of malonyl-CoA over other short-chain acyl-CoA esters, resemble those of carnitine palmitoyltransferase (CPT)-I, suggesting that the regulation of COT and CPT-I in parallel may be necessary for the control of cellular fatty acid metabolism.
Biochem J 1992 Sep 01
PMID:Malonyl-CoA inhibition of peroxisomal carnitine octanoyltransferase. 153 May 96

Regulation of in vitro palmitate metabolism by carnitine and propionate was investigated in liver obtained by biopsy from fasted nonlactating cows and from cows during early lactation. Liver slices from nonlactating cows during a 7-d fast esterified less palmitate than those from the same cows before fasting. Carnitine added in vitro increased hepatic oxidation and decreased esterification of palmitate in fed cows, but effects of carnitine were less during fasting. Propionate added in vitro decreased oxidation of palmitate; the effect was greater during fasting. In liver slices from cows during early lactation, carnitine increased oxidation and total utilization of palmitate and decreased palmitate esterification. Addition of tetradecylglycidic acid, an inhibitor of carnitine palmitoyltransferase I, prevented the carnitine-induced changes in palmitate metabolism. Substantial carnitine-independent oxidation of palmitate was observed in the presence of tetradecylglycidic acid. Tetradecylglycidic acid decreased esterification of palmitate to triglycerides but increased esterification to diglycerides. Effects of tetradecylglycidic acid and either propionate or pyruvate on palmitate oxidation were additive, indicating that propionate and pyruvate affect palmitate oxidation at sites other than carnitine palmitoyltransferase I. No interactions were detected between carnitine and propionate, but both compounds were potent regulators of palmitate metabolism in liver slices from cows during early lactation.
J Dairy Sci 1991 Sep
PMID:Regulation of in vitro metabolism of palmitate by carnitine and propionate in liver from dairy cows. 177 55


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