Branched-chain amino acid metabolism and alanine formation in rat diaphragm muscle in vitro. Effects of dichloroacetate.
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ABSTRACT:
SUBMITTER: Snell K
PROVIDER: S-EPMC1144369 | biostudies-other | 1984 Nov
REPOSITORIES: biostudies-other
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Project description:Muscle branched-chain amino acid metabolism is coupled to alanine formation via branched-chain amino acid aminotransferase and alanine aminotransferase, but the subcellular distributions of these and other associated enzymes are uncertain. Recovery of branched-chain aminotransferase in the cytosol fraction after differential centrifugation was shown to be accompanied by leakage of mitochondrial-matrix marker enzymes. By using a differential fractional extraction procedure, most of the branched-chain aminotransferase activity in rat muscle was located in the mitochondrial compartment, whereas alanine aminotransferase was predominantly in the cytosolic compartment. Phosphoenolpyruvate carboxykinase, like aspartate aminotransferase, was approximately equally distributed between these subcellular compartments. This arrangement necessitates a transfer of branched-chain amino nitrogen and carbon from the mitochondria to the cytosol for alanine synthesis de novo to occur. In incubations of hemidiaphragms from 48 h-starved rats with 3mM-valine or 3mM-glutamate, the stimulation of alanine release was inhibited by 69% by 1 mM-aminomethoxybut-3-enoate, a selective inhibitor of aspartate aminotransferase. Leucine-stimulated alanine release was unaffected. These data implicate aspartate aminotransferase in the transfer of amino acid carbon and nitrogen from the mitochondria to the cytosol, and suggest that oxaloacetate, via phosphoenolpyruvate carboxykinase, can serve as an intermediate on the route of pyruvate formation for muscle alanine synthesis.
| S-EPMC1144651 | biostudies-other
Project description:ObjectivePlasma levels of branched-chain amino acids (BCAA) are consistently elevated in obesity and type 2 diabetes (T2D) and can also prospectively predict T2D. However, the role of BCAA in the pathogenesis of insulin resistance and T2D remains unclear.MethodsTo identify pathways related to insulin resistance, we performed comprehensive gene expression and metabolomics analyses in skeletal muscle from 41 humans with normal glucose tolerance and 11 with T2D across a range of insulin sensitivity (SI, 0.49 to 14.28). We studied both cultured cells and mice heterozygous for the BCAA enzyme methylmalonyl-CoA mutase (Mut) and assessed the effects of altered BCAA flux on lipid and glucose homeostasis.ResultsOur data demonstrate perturbed BCAA metabolism and fatty acid oxidation in muscle from insulin resistant humans. Experimental alterations in BCAA flux in cultured cells similarly modulate fatty acid oxidation. Mut heterozygosity in mice alters muscle lipid metabolism in vivo, resulting in increased muscle triglyceride accumulation, increased plasma glucose, hyperinsulinemia, and increased body weight after high-fat feeding.ConclusionsOur data indicate that impaired muscle BCAA catabolism may contribute to the development of insulin resistance by perturbing both amino acid and fatty acid metabolism and suggest that targeting BCAA metabolism may hold promise for prevention or treatment of T2D.
| S-EPMC5034611 | biostudies-literature
Project description:Alanine production and pyruvate content of the isolated rat hemidiaphragm are increased by isoleucine or glutamate. These results support the hypothesis that amino acids are converted into pyruvate before oxidation and that some pyruvate is transaminated to alanine, which is released from the muscle.
| S-EPMC1172735 | biostudies-other
Project description:The three essential branched-chain amino acids (BCAAs), leucine, isoleucine and valine, share the first enzymatic steps in their metabolic pathways, including a reversible transamination followed by an irreversible oxidative decarboxylation to coenzyme-A derivatives. The respective oxidative pathways subsequently diverge and at the final steps yield acetyl- and/or propionyl-CoA that enter the Krebs cycle. Many disorders in these pathways are diagnosed through expanded newborn screening by tandem mass spectrometry. Maple syrup urine disease (MSUD) is the only disorder of the group that is associated with elevated body fluid levels of the BCAAs. Due to the irreversible oxidative decarboxylation step distal enzymatic blocks in the pathways do not result in the accumulation of amino acids, but rather to CoA-activated small carboxylic acids identified by gas chromatography mass spectrometry analysis of urine and are therefore classified as organic acidurias. Disorders in these pathways can present with a neonatal onset severe-, or chronic intermittent- or progressive forms. Metabolic instability and increased morbidity and mortality are shared between inborn errors in the BCAA pathways, while treatment options remain limited, comprised mainly of dietary management and in some cases solid organ transplantation.
| S-EPMC5685199 | biostudies-literature
Project description:Branched‐chain amino acid (BCAA) metabolism is a central hub for energy production and regulation of numerous physiological processes. Controversially, both increased and decreased levels of BCAAs are associated with longevity. Using genetics and multi‐omics analyses in Caenorhabditis elegans, we identified adaptive regulation of the ubiquitin‐proteasome system (UPS) in response to defective BCAA catabolic reactions after the initial transamination step. Worms with impaired BCAA metabolism show a slower turnover of a GFP‐based proteasome substrate, which is suppressed by loss‐of‐function of the first BCAA catabolic enzyme, the branched‐chain aminotransferase BCAT‐1. The exogenous supply of BCAA‐derived carboxylic acids, which are known to accumulate in the body fluid of patients with BCAA metabolic disorders, is sufficient to regulate the UPS. The link between BCAA intermediates and UPS function presented here sheds light on the unexplained role of BCAAs in the aging process and opens future possibilities for therapeutic interventions.
2022-09-22 | GSE185451 | GEO
Project description:The importance of boron (B) for living organisms is a puzzling matter. Despite the long established essential micronutrient role of B for vascular plants, only recent research gave insights on the mechanisms of its uptake, transport and direct participation in cell-wall formation. Despite that its precise role in plant metabolism remains elusive. In an attempt to clarify the role of B in plant metabolism the gene expression profile of a persistent response to B suppression was evaluated. For that purpose, the transcriptional profile of Arabidopsis thaliana subjected to 2 days of B deficiency was analyzed and the genes that kept responding 4 days after B deficiency were selected. The gene expression profile of Arabidopsis plants submitted to Ca deficiency was also evaluated and this data cross-compared with the 2 days transcriptional profile obtained under B deficiency.
2015-12-25 | GSE67768 | GEO
Project description:In theory, the complete oxidation to CO2 of amino acids that are metabolized by conversion into tricarboxylic acid-cycle intermediates may proceed via their conversion into acetyl-CoA. The possible adrenergic modulation of this oxidative pathway was investigated in isolated hemidiaphragms from 40 h-starved rats. Adrenaline (5.5 microM), phenylephrine (0.49 mM) and dibutyryl cyclic AMP (10 microM) inhibited 14CO2 production from 3 mM-[U-14C]valine by 35%, 28% and 19% respectively. At the same time, these agents stimulated glycogen mobilization (measured as a decrease in glycogen content) and glycolysis (measured as lactate release). Adrenaline, phenylephrine and dibutyryl cyclic AMP did not inhibit 14CO2 production from 3 mM-[U-14C]aspartate or 3 mM-[U-14C]glutamate, although, as in the presence of valine, the agents stimulated glycogen mobilization and glycolysis. The rate of proteolysis (measured as tyrosine release in the presence of cycloheximide) was not changed by adrenaline. The data indicate that the adrenergic inhibition of 14CO2 production from [U-14C]valine was not a consequence of radiolabel dilution. Inhibition was apparently specific for branched-chain amino acid metabolism in that the adrenergic agonists also inhibited 14CO2 production from [1-14C]valine, [1-14C]leucine and [U-14C]isoleucine. Since 14CO2 production from the 1-14C-labelled substrates is a specific measure of decarboxylation in the reaction catalysed by the branched-chain 2-oxo acid dehydrogenase complex, it is at this site that the adrenergic agents are concluded to act.
| S-EPMC1152470 | biostudies-other
Project description:Peroxisome proliferator-activated receptor (PPAR) ? coactivator 1? (PGC-1?) is a coactivator of various nuclear receptors and other transcription factors, which is involved in the regulation of energy metabolism, thermogenesis, and other biological processes that control phenotypic characteristics of various organ systems including skeletal muscle. PGC-1? in skeletal muscle is considered to be involved in contractile protein function, mitochondrial function, metabolic regulation, intracellular signaling, and transcriptional responses. Branched-chain amino acid (BCAA) metabolism mainly occurs in skeletal muscle mitochondria, and enzymes related to BCAA metabolism are increased by exercise. Using murine skeletal muscle overexpressing PGC-1? and cultured cells, we investigated whether PGC-1? stimulates BCAA metabolism by increasing the expression of enzymes involved in BCAA metabolism. Transgenic mice overexpressing PGC-1? specifically in the skeletal muscle had increased the expression of branched-chain aminotransferase (BCAT) 2, branched-chain ?-keto acid dehydrogenase (BCKDH), which catabolize BCAA. The expression of BCKDH kinase (BCKDK), which phosphorylates BCKDH and suppresses its enzymatic activity, was unchanged. The amount of BCAA in the skeletal muscle was significantly decreased in the transgenic mice compared with that in the wild-type mice. The amount of glutamic acid, a metabolite of BCAA catabolism, was increased in the transgenic mice, suggesting the activation of muscle BCAA metabolism by PGC-1?. In C2C12 cells, the overexpression of PGC-1? significantly increased the expression of BCAT2 and BCKDH but not BCKDK. Thus, PGC-1? in the skeletal muscle is considered to significantly contribute to BCAA metabolism.
| S-EPMC3956461 | biostudies-other
Project description:Alanine release by rat diaphragm muscle in vitro is stimulated by glutamate, valine, leucine and glucose. The stimulation by glutamate and valine (but not leucine) is inhibited by 3-mercaptopicolinate. These results suggest a metabolic route involving phosphoenolpyruvate carboxykinase which directs amino acid carbon skeletons towards pyruvate synthesis for alanine formation.
| S-EPMC1164613 | biostudies-other
Project description:Commercial preparations of alanine dehydrogenase from Bacillus subtilis are contaminated to varying extents with activity towards branched-chain amino acids. The Km values for these amino acids are of the same order as for L-alanine (about 10(-3)M). The branched-chain amino acid dehydrogenase activity is lost on dialysis for 2--4h against water or 2mM-EDTA.
| S-EPMC1186017 | biostudies-other