Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.16 (calcineurin)
 17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

When isolated rat hepatocytes were cultured in the medium containing 0.5 mM clofibrate (dissolved in ethanol) for 6 hours, the activity of branched-chain alpha-keto acid dehydrogenase (BCKADH) complex in the cells increased to more than two times that of control cells. Immunochemical determination with an anti-BCKADH IgG revealed that the activity increase occurred without increase in the enzyme amount. On the contrary, BCKADH activity in control cells (cultured in the presence 0.4% ethanol) decreased to two-third the initial activity at the end of 6-hour incubation whereas the activities of other enzymes tested were practically unaltered either in control or in clofibrate-treated cells. When the control cell extract was incubated with rat liver protein phosphatase, the BCKADH activity increased near to that of clofibrate-treated cells, but the same treatment of clofibrate-treated cell extract produced practically no increase in the activity. These observations indicate that clofibrate addition brought about the increase of BCKADH activity through activation-inactivation mechanism based on dephosphorylation-phosphorylation, and that this mechanism might function on liver BCKADH complex in vivo as a short term control of the activity in some conditions.
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PMID:Control of the activity of branched-chain alpha-keto acid dehydrogenase complex in primary cultured rat hepatocytes. 263 19

A potent, heat-stable protein inhibitor of branched-chain alpha-keto acid dehydrogenase (BCKDH) phosphatase has been identified and purified to near homogeneity from bovine kidney mitochondria (Damuni, Z., Humphreys, J. S., and Reed, L. J., Proc. Natl. Acad. Sci. U.S.A., in press). This protein is a noncompetitive inhibitor of BCKDH phosphatase, with a Ki about 0.13 nM. By contrast, this protein inhibitor did not affect the activity of the cytosolic protein phosphatase-1 and phosphatase-2A or the mitochondrial pyruvate dehydrogenase (PDH) phosphatase at concentrations up to 10 nM. The cytosolic protein phosphatase inhibitor-1 and inhibitor-2 had no effect on the activity of BCKDH phosphatase or PDH phosphatase at concentrations up to 50 and 300 nM respectively. These results, together with previous evidence, demonstrate that BCKDH phosphatase and its inhibitor protein are distinct from the cytosolic protein phosphatase-1 and phosphatase-2A and from protein phosphatase inhibitor-1 and inhibitor-2, respectively.
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PMID:Specificity of the heat-stable protein inhibitor of the branched-chain alpha-keto acid dehydrogenase phosphatase. 300 73

The catalytic subunit of the branched-chain alpha-keto acid dehydrogenase (BCKDH) phosphatase (Damuni, Z., Merryfield, M.L., Humphreys, J.S., and Reed, L.J., (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 4335-4338) has been purified over 50,000-fold from extracts of bovine kidney mitochondria. The apparently homogeneous protein consists of a single polypeptide chain with an apparent Mr = approximately 33,000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. BCKDH phosphatase, with an apparent Mr = 460,000, was dissociated to its catalytic subunit with no apparent change in activity, at an early stage in the purification procedure by treatment with 6 M urea. The specific activity of the catalytic subunit was 1,500-2,500 units/mg. The catalytic subunit exhibited approximately 10% maximal activity with 32P-labeled pyruvate dehydrogenase complex but was inactive with phosphorylase a and with p-nitrophenyl phosphate. The catalytic subunit, like the Mr = 460,000 species, was inhibited by nanomolar concentrations of BCKDH phosphatase inhibitor protein, was unaffected by protein phosphatase inhibitor 1 and inhibitor 2, and was inhibited by nucleoside tri- and diphosphates but not by nucleoside monophosphates.
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PMID:Purification and properties of the catalytic subunit of the branched-chain alpha-keto acid dehydrogenase phosphatase from bovine kidney mitochondria. 303 Oct 42

A heat- and acid-stable protein inhibitor of the [branched-chain alpha-keto acid dehydrogenase]-phosphatase was purified over 100,000-fold from extracts of bovine kidney mitochondria. The nearly homogeneous protein was recovered with a yield of 4-8%. The apparent molecular weight of the inhibitor is about 36,000. This protein is a noncompetitive inhibitor of the phosphatase, and the inhibitor constant (Ki) is about 0.13 nM. The inhibition was reversed 50% by about 1.3 mM Mg2+ and about 0.1 mM spermine. This protein inhibitor is different from the cytosolic protein phosphatase inhibitors 1 and 2.
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PMID:A potent, heat-stable protein inhibitor of [branched-chain alpha-keto acid dehydrogenase]-phosphatase from bovine kidney mitochondria. 345 64

An assay is described to define the proportion of the branched-chain 2-oxo acid dehydrogenase complex that is present in the active state in rat tissues. Activities are measured in homogenates in two ways: actual activities, present in tissues, by blocking both the kinase and phosphatase of the enzyme complex during homogenization, preincubation, and incubation with 1-14C-labelled branched-chain 2-oxo acid, and total activities by blocking only the kinase during the 5 min preincubation (necessary for activation). The kinase is blocked by 5 mM-ADP and absence of Mg2+ and the phosphatase by the simultaneous presence of 50 mM-NaF. About 6% of the enzyme is active in skeletal muscle of fed rats, 7% in heart, 20% in diaphragm, 47% in kidney, 60% in brain and 98% in liver. An entirely different assay, which measures activities in crude tissue extracts before and after treatment with a broad-specificity protein phosphatase, gave similar results for heart, liver and kidney. Advantages of our assay with homogenates are the presence of intact mitochondria, the simplicity, the short duration and the high sensitivity. The actual activities measured indicate that the degradation of branched-chain 2-oxo acids predominantly occurs in liver and kidney and is limited in skeletal muscle in the fed state.
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PMID:The activity state of the branched-chain 2-oxo acid dehydrogenase complex in rat tissues. 643 Feb 80

The BCKDH (branched-chain alpha-keto acid dehydrogenase complex) catalyses the rate-limiting step in the oxidation of BCAAs (branched-chain amino acids). Activity of the complex is regulated by a specific kinase, BDK (BCKDH kinase), which causes inactivation, and a phosphatase, BDP (BCKDH phosphatase), which causes activation. In the present study, the effect of the disruption of the BDK gene on growth and development of mice was investigated. BCKDH activity was much greater in most tissues of BDK-/- mice. This occurred in part because the E1 component of the complex cannot be phosphorylated due to the absence of BDK and also because greater than normal amounts of the E1 component were present in tissues of BDK-/- mice. Lack of control of BCKDH activity resulted in markedly lower blood and tissue levels of the BCAAs in BDK-/- mice. At 12 weeks of age, BDK-/- mice were 15% smaller than wild-type mice and their fur lacked normal lustre. Brain, muscle and adipose tissue weights were reduced, whereas weights of the liver and kidney were greater. Neurological abnormalities were apparent by hind limb flexion throughout life and epileptic seizures after 6-7 months of age. Inhibition of protein synthesis in the brain due to hyperphosphorylation of eIF2alpha (eukaryotic translation initiation factor 2alpha) might contribute to the neurological abnormalities seen in BDK-/- mice. BDK-/- mice show significant improvement in growth and appearance when fed a high protein diet, suggesting that higher amounts of dietary BCAA can partially compensate for increased oxidation in BDK-/- mice. Disruption of the BDK gene establishes that regulation of BCKDH by phosphorylation is critically important for the regulation of oxidative disposal of BCAAs. The phenotype of the BDK-/- mice demonstrates the importance of tight regulation of oxidative disposal of BCAAs for normal growth and neurological function.
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PMID:Impaired growth and neurological abnormalities in branched-chain alpha-keto acid dehydrogenase kinase-deficient mice. 1706 58

Branched-chain amino acids (BCAA) have increasingly been studied as playing a role in diabetes, with the PubMed search string "diabetes" AND "branched chain amino acids" showing particular growth in studies of the topic over the past decade (Fig. ). In the Young Finn's Study, BCAA and, to a lesser extent, the aromatic amino acids phenylalanine and tyrosine were associated with insulin resistance (IR) in men but not in women, whereas the gluconeogenic amino acids alanine, glutamine, or glycine, and several other amino acids (i.e. histidine, arginine, and tryptophan) did not show an association with IR. Obesity may track more strongly than metabolic syndrome and diabetes with elevated BCAA. In a study of 1302 people aged 40-79; higher levels of BCAA tracked with older age, male sex, and metabolic syndrome, as well as with obesity, cardiovascular risk, dyslipidemia, hypertension, and uric acid. Medium- and long-chain acylcarnitines, by-products of mitochondrial catabolism of BCAAs, as well as branched-chain keto acids and the BCAA themselves distinguished obese people having versus not having features of IR, and in a study of 898 patients with essential hypertension, the BCAA and tyrosine and phenylalanine were associated with metabolic syndrome and impaired fasting glucose. In a meta-analysis of three genome-wide association studies, elevations in BCAA and, to a lesser extent, in alanine tracked with IR, whereas higher levels of glutamine and glycine were associated with lesser likelihood of IR. Given these associations with IR, it is not surprising that a number of studies have shown higher BCAA levels in people with and prior to development of type 2 diabetes (T2D), although this has particularly been shown in Caucasian and Asian ethnic groups while not appearing to occur in African Americans. Similarly, higher BCAA levels track with cardiovascular disease. [Figure: see text] The metabolism of BCAA involves two processes: (i) a reversible process catalysed by a branched-chain aminotransferase (BCAT), either cytosolic or mitochondrial, requiring pyridoxal to function as an amino group carrier, by which the BCAA with 2-ketoglutarate produce a branched-chain keto acid plus glutamate; and (ii) the irreversible mitochondrial process catalysed by branched-chain keto acid dehydrogenase (BCKDH) leading to formation of acetyl-coenzyme A (CoA), propionyl-CoA, and 2-methylbutyryl-CoA from leucine, valine, and isoleucine, respectively, which enter the tricarboxylic acid (Krebs) cycle as acetyl-CoA, propionyl-CoA, and 2-methylbutyryl-CoA, respectively, leading to ATP formation. The BCAA stimulate secretion of both insulin and glucagon and, when given orally, of both glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), with oral administration leading to greater and more prolonged insulin and glucagon secretion. Insulin may particularly reduce BCAA turnover to a greater extent than that of other amino acids, and decreases the appearance and increases the uptake of amino acids. However, older studies of the effect of glucose or insulin on BCAA concentrations and rates of leucine appearance and oxidation showed no reduction in T2D, although the higher baseline levels of BCAA in obesity have long been recognized. Impaired function of BCAT and BCKDH has been posited, either as a primary genetic abnormality or due to effects of elevated fatty acids, proinflammatory cytokines, or insulin levels with consequent accumulation of branched-chain keto acids and metabolites such as diacylglycerol and ceramide, potentially contributing to the development of further insulin resistance, and decreased skeletal muscle BCAT and BCKDH expression has been shown in people with diabetes, supporting this concept. A Mendelian randomization study used measured variation in genes involved in BCAA metabolism to test the hypothesis of a causal effect of modifiable exposure on IR, showing that variants in protein phosphatase, Mg2+ /Mn2+ dependent 1K (PPM1K), a gene encoding the mitochondrial phosphatase activating the BCKDH complex, are associated with T2D, but another such study suggested that genetic variations associated with IR are causally related to higher BCAA levels. Another hypothesis involves the mammalian target of rapamycin complex 1 (mTORC1), which is activated by BCAA, as well as by insulin and glucose via cellular ATP availability. If this is the relevant pathway, BCAA overload may cause insulin resistance by activation of mammalian target of rapamycin (mTOR), as well as by leading to increases in acylcarnitines, with mTOR seen in this scenario as a central signal of cross-talk between the BCAA and insulin. At this point, whether whole-body or tissue-specific BCAA metabolism is increased or decreased in states of insulin-resistant obesity and T2D is uncertain. Insulin action in the hypothalamus induces but overfeeding decreases hepatic BCKDH, leading to the concept that hypothalamic insulin resistance impairs BCAA metabolism in obesity and diabetes, so that plasma BCAAs may be markers of hypothalamic insulin action rather than direct mediators of changes in IR. A way to address this may be to understand the effects of changes in diet and other interventions on BCAA, as well as on IR and T2D. In an animal model, lowering dietary BCAA increased energy expenditure and improved insulin sensitivity. Two large human population studies showed an association of estimated dietary BCAA intake with T2D risk, although another population study showed higher dietary BCAA to be associated with lower T2D risk. Ethnic differences, reflecting underlying differences in genetic variants, may be responsible for such differences. In the study of Asghari et al. in the current issue of the Journal of Diabetes, BCAA intake was associated with the development of subsequent IR. Studies of bariatric surgery suggest lower basal and post-insulin infusion BCAA levels are associated with greater insulin sensitivity, with reductions in BCAA not seen with weight loss per se with gastric band procedures, but occurring after Roux-en-Y gastric bypass, an intervention that may have metabolic benefits over and above those from reduction in body weight. The gut microbiota may be important for the supply of the BCAA to mammalian hosts, either by de novo biosynthesis or by modifying nutrient absorption. A final fascinating preliminary set of observations is that of the effects of empagliflozin on metabolomics; evidence of increased Krebs cycle activation and of higher levels of BCAA metabolites, such as acylcarnitines, suggests that sodium-glucose cotransporter 2 (SGLT2) inhibition may, to some extent, involve BCAA metabolism. Certainly, we do not yet have a full understanding of these complex associations. However, the suggestion of multiple roles of BCAA in the development of IR promises to be important and to lead to the development of novel effective T2D therapies.
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PMID:Diabetes and branched-chain amino acids: What is the link? 2936 29

Branched chained amino acids (BCAA) are essential components of the human diet and important nutrient signals, which regain particular interest in recent years with the avenue of metabolomics studies suggesting their potential role as biomarkers. There is now compelling evidence for predictive role of BCAA in progression of diabetes, but causality relationship is still debated concerning insulin resistance and genetic versus non-genetic pathogenesis. Mendelian randomization studies in large cohorts of diabetes indicated pathogenic role of PPM1K (protein phosphatase Mg2+/Mn2+ dependent 1K) on Chr 4q22.1 gene, encoding for a phosphatase that activates BCKDH (branched chain keto acid dehydrogenase) complex. Recent studies indicated that insulin rapidly and dose-dependently regulates gene expression of the same complex, but the relationship with systemic insulin resistance and glucose levels is complex. Rare genetic syndromes due to Mendelian mutations in key genes in BCAA catabolism may be good models to understand potential role of gene of BCAA catabolism. However, in studying complex disorders geneticists are faced to complete new aspects of metabolic regulation complicating understanding genetics of obesity, diabetes or metabolic syndrome. A review of genetic syndromes of BCAA metabolism suggests that insulin resistance is not present, except rare cases of methylmalonic aciduria due to MUT (methylmalonyl-coA mutase) gene on Chr 6p12.3. Another aspect that complicates understanding is the new role of central nervous system (CNS) in insulin resistance. For a long time the hypothalamic hunger/satiety neuronal system was considered a key site of nutrient regulation. Genes may also affect the brain rewarding system (BRS) that would regulate food intake by modulating the motivation to obtain food and considering hedonic properties. Nutrigenomic and nutrigenetic investigations taking into account concurrently BCAA intake, metabolic regulation and gene variation have large perspectives to merge genetic and nutritional understanding in complex disorders.
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PMID:BRANCHED CHAIN AMINO ACIDS AT THE EDGE BETWEEN MENDELIAN AND COMPLEX DISORDERS. 3114 64