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

---

Query: EC:6.4.1.1 (pyruvate carboxylase)
1,516 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In islet beta-cells and INS-1 cells both the high activity of malic enzyme and the correlation of insulin secretion rates with pyruvate carboxylase (PC) flux suggest that a pyruvate-malate cycle is functionally relevant to insulin secretion. Expression of the malic enzyme isoforms in INS-1 cells and rat islets was measured, and small interfering RNA was used to selectively reduce isoform mRNA expression in INS-1 cells to evaluate its impact on insulin secretion. The cytosolic NADP(+)-specific isoform (ME1) was the most abundant, with the mitochondrial isoforms NAD(+)-preferred (ME2) expressed at approximately 50%, and the NADP(+)-specific (ME3) at approximately 10% compared with ME1. Selective reduction (89 +/- 2%) of cytosolic ME1 mRNA expression and enzyme activity significantly reduced glucose (15 mM:41 +/- 6%, p < 0.01) and amino acid (4 mM glutamine +/- 10 mM leucine: 39 +/- 6%, p < 0.01)-stimulated insulin secretion. Selective small interfering RNA reduction (51 +/- 6%) of mitochondrial ME2 mRNA expression did not impact glucose-induced insulin secretion, but decreased amino acid-stimulated insulin secretion by 25 +/- 4% (p < 0.01). Modeling of the metabolism of [U-(13)C]glucose by its isotopic distribution in glutamate indicates a second pool of pyruvate distinct from glycolytically derived pyruvate in INS-1 cells. ME1 knockdown decreased flux of both pools of pyruvate through PC. In contrast, ME2 knockdown affected only PC flux of the pyruvate derived from glutamate metabolism. These results suggest a physiological basis for two metabolically and functionally distinct pyruvate cycles. The cycling of pyruvate by ME1 generates cytosolic NADPH, whereas mitochondrial ME2 responds to elevated amino acids and serves to supply sufficient pyruvate for increased Krebs cycle flux when glucose is limiting.
...
PMID:Cytosolic and mitochondrial malic enzyme isoforms differentially control insulin secretion. 1710 38

Pancreatic preservation is an important part of diabetes management that may occur with improved peripheral insulin sensitivity and attenuated low-grade adipose tissue inflammation. The objective of the current study was to determine the response of obese, insulin-resistant fa/fa Zucker rats vs lean controls to dietary conjugated linoleic acid (CLA) supplementation with respect to pancreatic islet size, insulin resistance, and markers of inflammation and adipose glucose uptake. Six-week-old fa/fa and lean Zucker rats (n = 20 per genotype) were fed either a 1.5% CLA mixture or control diet for 8 weeks. Oral glucose tolerance testing was conducted at 7.5 weeks. Fasting serum haptoglobin, insulin, and C-peptide were assayed, and select messenger RNA (mRNA) and protein markers of inflammation and glucose metabolism were measured in adipose and liver tissues. CLA-fed fa/fa Zucker rats had smaller islet cell size, improved oral glucose tolerance and insulinemia, and attenuated serum haptoglobin levels compared with control-fed fa/fa Zucker rats, despite no differences in body weight and a slightly higher visceral adipose mass. CLA did not alter insulin sensitivity or islet size in lean Zucker rats. The CLA-fed fa/fa rats also had greater adipose glucose transporter-4 mRNA and less adipose tumor necrosis factor alpha mRNA and protein compared with control-fed fa/fa rats. In contrast, other markers of inflammation and glucose metabolism including adipose macrophage inflammatory factor, macrophage inflammatory protein-2, and liver pyruvate carboxylase and pyruvate dehydrogenase kinase 4 were not significantly changed. These results suggest that CLA supplementation preserved pancreatic function in conjunction with improved peripheral glucose use and reduced inflammation in fa/fa Zucker rats.
...
PMID:Dietary conjugated linoleic acid preserves pancreatic function and reduces inflammatory markers in obese, insulin-resistant rats. 1716 Dec 37

PC (pyruvate carboxylase) plays a crucial role in intermediary metabolism including glucose-induced insulin secretion in pancreatic islets. In the present study, we identified two regions of the 1.2 kb distal promoter, the -803/-795 site and the -408/-403 E-box upstream of the transcription start site, as the important cis-acting elements for transcriptional activation of the luciferase reporter gene. Site-directed mutagenesis of either one of these sites in the context of this 1.2 kb promoter fragment, followed by transient transfections in the insulinoma cell line, INS-1, abolished reporter activity by approx. 50%. However, disruption of either the -803/-795 or the -408/-403 site did not affect reporter gene activity in NIH 3T3 cells, suggesting that this promoter fragment is subjected to cell-specific regulation. The nuclear proteins that bound to these -803/-795 and -408/-403 sites were identified by gel retardation assays as HNF3beta (hepatocyte nuclear factor 3beta)/Foxa2 (forkhead/winged helix transcription factor box2) and USFs (upstream stimulatory factors), USF1 and USF2, respectively. Chromatin immunoprecipitation assays using antisera against HNF3beta/Foxa2, USF1 and USF2 demonstrated that endogenous HNF3beta/Foxa2 binds to the -803/-795 Foxa2 site, and USF1 and USF2 bind to the -408/-403 E-box respectively in vivo, consistent with the gel retardation assay results. Although there are weak binding sites located at regions -904 and -572 for PDX1 (pancreatic duodenal homeobox-1), a transcription factor that controls expression of beta-cell-specific genes, it did not appear to regulate PC expression in INS-1 cells in the context of the 1.2 kb promoter fragment. The results presented here show that Foxa2 and USFs regulate the distal promoter of the rat PC gene in a cell-specific manner.
...
PMID:Transcriptional regulation of the distal promoter of the rat pyruvate carboxylase gene by hepatocyte nuclear factor 3beta/Foxa2 and upstream stimulatory factors in insulinoma cells. 1740 83

Pyruvate carboxylase (PC) catalyzes the biotin-dependent production of oxaloacetate and has important roles in gluconeogenesis, lipogenesis, insulin secretion and other cellular processes. PC contains the biotin carboxylase (BC), carboxyltransferase (CT) and biotin-carboxyl carrier protein (BCCP) domains. We report here the crystal structures at 2.8-A resolution of full-length PC from Staphylococcus aureus and the C-terminal region (missing only the BC domain) of human PC. A conserved tetrameric association is observed for both enzymes, and our structural and mutagenesis studies reveal a previously uncharacterized domain, the PC tetramerization (PT) domain, which is important for oligomerization. A BCCP domain is located in the active site of the CT domain, providing the first molecular insights into how biotin participates in the carboxyltransfer reaction. There are dramatic differences in domain positions in the monomer and the organization of the tetramer between these enzymes and the PC from Rhizobium etli.
...
PMID:Crystal structures of human and Staphylococcus aureus pyruvate carboxylase and molecular insights into the carboxyltransfer reaction. 1829 87

Multiparous Holstein cows (n=58) were used to study the effects of peripartum dietary supplementation on metabolic status, liver function and reproduction variables. Diets for cows were as follows: (a) no supplementation (CTL), (b) prilled fatty acids as 1.9% of DM (PrFA), (c) calcium salts of long chain n-6 fatty acids as 2.24% of DM (CaLFA) or (d) daily topdressing with 769 g of 65% propylene glycol (PGLY). Supplements were fed during the last 21 days before expected calving except for PGLY that continued until 21 days after parturition. Ovarian activity was monitored by transrectal ultrasonography and days to first ovulation were recorded. Liver biopsies were obtained on day 8 and 21 postpartum and analyzed for triglyceride content and mRNA expression of pyruvate carboxylase, cytosolic phosphoenolpyruvate carboxykinase, carnitine palmytoyltransferase 1A, and peroxisome proliferator-activated receptor-alpha. At 71 days following parturition, stage of ovarian cycles was synchronized and at day15 of the cycle oxytocin was injected i.v., blood samples were obtained at frequent intervals, and analyzed for 13,14 dihydro, 15-keto PGF(2alpha) (PGFM). Milk production and milk components were not different among treatment groups. Cows in PGLY gained body condition score (BCS) prepartum and net energy balance prepartum tended to be greater, but was not different postpartum from other groups. PGLY supplementation increased plasma insulin concentration prepartum, but not during the postpartum period. No significant differences were observed in plasma concentrations of glucose, NEFA, and insulin-like growth factor or hepatic triglyceride content, but all supplements tended to decrease beta hydroxybutyrate postpartum compared to CTL cows. Abundance of mRNA of gluconeogenic and lipid oxidation genes was not different among treatment groups. Days to first ovulation and uterine PGF(2alpha) production in response to an oxytocin treatment were not significantly different among treatment groups. Peripartum supplementation did not result in the substantial improvement of metabolic profile in early lactation nor significantly affect days to first ovulation and PGFM response to an oxytocin treatment.
...
PMID:Effect of peripartum dietary energy supplementation of dairy cows on metabolites, liver function and reproductive variables. 1853 91

PC (pyruvate carboxylase) is a biotin-containing enzyme that catalyses the HCO(3)(-)- and MgATP-dependent carboxylation of pyruvate to form oxaloacetate. This is a very important anaplerotic reaction, replenishing oxaloacetate withdrawn from the tricarboxylic acid cycle for various pivotal biochemical pathways. PC is therefore considered as an enzyme that is crucial for intermediary metabolism, controlling fuel partitioning toward gluconeogenesis or lipogenesis and in insulin secretion. The enzyme was discovered in 1959 and over the last decade there has been much progress in understanding its structure and function. PC from most organisms is a tetrameric protein that is allosterically regulated by acetyl-CoA and aspartate. High-resolution crystal structures of the holoenzyme with various ligands bound have recently been determined, and have revealed details of the binding sites and the relative positions of the biotin carboxylase, carboxyltransferase and biotin carboxyl carrier domains, and also a unique allosteric effector domain. In the presence of the allosteric effector, acetyl-CoA, the biotin moiety transfers the carboxy group between the biotin carboxylase domain active site on one polypeptide chain and the carboxyltransferase active site on the adjacent antiparallel polypeptide chain. In addition, the bona fide role of PC in the non-gluconeogenic tissues has been studied using a combination of classical biochemistry and genetic approaches. The first cloning of the promoter of the PC gene in mammals and subsequent transcriptional studies reveal some key cognate transcription factors regulating tissue-specific expression. The present review summarizes these advances and also offers some prospects in terms of future directions for the study of this important enzyme.
...
PMID:Structure, mechanism and regulation of pyruvate carboxylase. 1861 15

The objective of the present study was to describe plasma hormonal and metabolite profile and mRNA expression levels and activities of the enzymes pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK), and acetyl-coenzyme A (CoA) carboxylase in the liver of male Holstein calves before (1 and 3 wk of age) and after (8, 13, and 19 wk of age) weaning at 6 wk of age. The mean plasma concentration of acetate and beta-hydroxybutyrate increased, and that of plasma lactate and nonesterified fatty acids decreased with week, particularly after weaning. Plasma glucose concentration was lowest at 8 wk of age. The mean plasma concentration of insulin and glucagon did not change with time, and that of cortisol was greatest at 1 wk of age. In the liver, enzyme activity of PC was greatest at 1 wk of age and decreased with time. There was a significant relationship between the activity and the mRNA level for PC. Activity of PEPCK also decreased with week. Acetyl-CoA carboxylase activity tended to decrease with week, and activity at 13 wk of age was lower than that at other times. Expression of PC mRNA, but not that of PEPCK and acetyl-CoA carboxylase alpha, decreased with week. We conclude that the hepatic gluconeogenic enzymes and acetyl-CoA carboxylase activities tend to decrease with age, reflecting changes in plasma metabolites in early weaning production systems.
...
PMID:Changes in hepatic key enzymes of dairy calves in early weaning production systems. 1865 Feb 92

Anaplerosis, the synthesis of citric acid cycle intermediates, by pancreatic beta cell mitochondria has been proposed to be as important for insulin secretion as mitochondrial energy production. However, studies designed to lower the rate of anaplerosis in the beta cell have been inconclusive. To test the hypothesis that anaplerosis is important for insulin secretion, we lowered the activity of pyruvate carboxylase (PC), the major enzyme of anaplerosis in the beta cell. Stable transfection of short hairpin RNA was used to generate a number of INS-1 832/13-derived cell lines with various levels of PC enzyme activity that retained normal levels of control enzymes, insulin content, and glucose oxidation. Glucose-induced insulin release was decreased in proportion to the decrease in PC activity. Insulin release in response to pyruvate alone, 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) plus glutamine, or methyl succinate plus beta-hydroxybutyrate was also decreased in the PC knockdown cells. Consistent with a block at PC, the most PC-deficient cells showed a metabolic crossover point at PC with increased basal and/or glucose-stimulated pyruvate plus lactate and decreased malate and citrate. In addition, in BCH plus glutamine-stimulated PC knockdown cells, pyruvate plus lactate was increased, whereas citrate was severely decreased, and malate and aspartate were slightly decreased. The incorporation of 14C into lipid from [U-14C]glucose was decreased in the PC knockdown cells. The results confirm the central importance of PC and anaplerosis to generate metabolites from glucose that support insulin secretion and even suggest PC is important for insulin secretion stimulated by noncarbohydrate insulin secretagogues.
...
PMID:Impaired anaplerosis and insulin secretion in insulinoma cells caused by small interfering RNA-mediated suppression of pyruvate carboxylase. 1869 38

Therapeutic effect of rosiglitazone has been reported to result from an improvement of insulin sensitivity and inhibition of glucose synthesis. As the latter process occurs in both liver and kidney cortex the aim of this study was to elucidate the rosiglitazone action on glucose formation in both tissues. Primary cultured cells of both liver and kidney cortex grown in defined medium were use throughout. To identify the mechanism responsible for drug-induced changes, intracellular gluconeogenic intermediates and enzyme activities were determined. In contrast to hepatocytes, the administration of a 10 micromol/L concentration of rosiglitazone to renal tubules resulted in about a 70% decrease in the rate of gluconeogenesis, accompanied by an approximately 75% decrease in alanine utilization and a 35% increase in lactate synthesis. The effect of rosiglitazone was not abolished by GW9662, the PPAR-gamma irreversible antagonist, indicating that this action is not dependent on PPAR-gamma activation. In view of rosiglitazone-induced changes in gluconeogenic intermediates and a diminished incorporation of 14CO2 into pyruvate, it is likely that the drug causes a decline in flux through pyruvate carboxylase and (or) phosphoenolpyruvate carboxykinase. It is likely that the hypoglycemic action of rosiglitazone is PPAR-gamma independent and results mainly from its inhibitory effects on renal gluconeogenesis.
...
PMID:PPAR-gamma-independent inhibitory effect of rosiglitazone on glucose synthesis in primary cultured rabbit kidney-cortex tubules. 1892 41

Elevated liver fat content occurs in high-yielding dairy cows during the transition from pregnancy to lactation after fat mobilization and may affect hepatic glucose metabolism, but the degree of liver fat storage is highly variable. Therefore, we studied metabolic and endocrine changes and hepatic glucose metabolism in cows that markedly differ in liver fat content. Multiparous cows from the same herd with high (HFL; n = 10) and low (LFL; n = 10) liver fat contents (mean of d 1, 10, and 21 after calving for each cow, respectively) were studied from 60 d before expected calving to 56 d in milk. Cows were fed ad libitum and all cows received the same diets. Liver samples were taken on d 1, 10, and 21 after calving; mean fat content (+/-SEM) in liver of HFL cows was 174 +/- 9.6 mg/g, whereas mean liver fat content in LFL cows was 77 +/- 3.3 mg/g. Blood samples were taken 20 and 7 d before expected calving and 0, 7, 14, 28, and 56 d after calving to measure plasma concentrations of nonesterified fatty acids, beta-hydroxybutyrate, glucose, insulin, glucagon, insulin-like growth factor-I, and leptin. In liver, glycogen content as well as mRNA levels of phosphoenolpyruvate carboxykinase, pyruvate carboxylase, glucose-6-phosphatase, and glucose transporter were measured by quantitative real-time PCR. Back fat thickness decreased and dry matter intake increased with onset of lactation, and back fat thickness was higher but dry matter intake was lower in HFL than in LFL. Energy-corrected milk yield did not differ between groups, but milk fat content was higher and lactose content was lower in HFL than LFL at the beginning of lactation. Energy balance was more negative in HFL than in LFL. Plasma nonesterified fatty acids and beta-hydroxybutyrate concentrations increased and plasma glucose concentration tended to decrease more in HFL than LFL with onset of lactation. Glucagon to insulin ratios increased more in HFL than LFL with onset of lactation. Hepatic glycogen content was higher in LFL than HFL, whereas mRNA levels of glucose-6-phosphatase and pyruvate carboxylase were higher in HFL than in LFL, and cytosolic phosphoenolpyruvate carboxykinase mRNA level increased similarly after parturition in both groups. In conclusion, an elevated liver fat content was related to greater fat mobilization and reduced feed intake and was associated with effects on hepatic glucose metabolism. As environment and feeding management were the same, individual cow factors were responsible for differences in energy metabolism during the transition period.
...
PMID:Performance and metabolic and endocrine changes with emphasis on glucose metabolism in high-yielding dairy cows with high and low fat content in liver after calving. 1930 36


<< Previous 1 2 3 4 5 6 7 8 9 10

---