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:2.4.1.18 (branching enzyme)
628 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Q-Enzyme, the enzyme that synthesizes the 1,6-alpha-glucosidic branch linkages of amylopectin, has been purified from potato to near homogeneity. The molecular weight of the enzyme is 85000. The active enzyme is a monomer, with a molar activity at pH 7.0 and 24 degrees C of 15. The energy of activation is 25 kJ/mol below 15 degrees C, changing sharply to 63 kJ/mol above that temperature. Enzyme activity is not affected by Mg2+ or ATP. There are about 11 readily titratable sulfhydryl groups per molecule. The evidence that the enzyme is a single protein entity, without hydrolytic activity towards amylose, contrasts with an earlier report that Q-enzyme consists of two components, a hydrolase with molecular weight 70000, and a transferase with molecular weight 20000. Q-enzyme acts on native and synthetic amyloses to give products resembling amylopectin in terms of average unit chain length, degress of beta-amylolysis and iodine stain. The profiles of the unit chains of these synthetic products are, however, different from that of native amylopectin. Additional branch linkages are introduced by Q-enzyme into potato amylopectin, but the product bears no resemblance to phytoglycogen.
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PMID:Purification and properties of potato 1,4-alpha-D-glucan:1,4-alpha-D-glucan 6-alpha-(1,4-alpha-glucano)-transferase. Evidence against a dual catalytic function in amylose-branching enzyme. 0 Dec 58

An Escherichia coli B mutant, SG14, accumulates glycogen at 28% the rate observed for the parent E. coli B strain. The glycogen accumulated in the mutant is similar to the glycogen isolated from the parent strain with respect to alpha- and beta-amylosis, chain length determination, and I2-complex absorption spectra. The SG14 mutant contains normal glycogen synthase and branching enzyme activity but has an ADP-glucose pyrophosphorylase with altered kinetic and allosteric properties. The mutant enzyme has been partially purified and requires a 12-fold higher concentration of fructose-P2 or a 26 fold higher concentration of pyridoxal-P than the parent type enzyme for 50% of maximal allosteric activation. TPNH, an effective activator of the E. coli B enzyme, does not activate the SG14 ADP-glucose pyrophosphorylase. Other studies show that for the SG14 enzyme the concentrations of ATP and Mg2+ in the synthesis direction and the concentrations of ADP-glucose and PPi in the pyrophosphorolysis direction required to give 50% of maximal activity are 3- to 6-fold higher than those observed for the parent E. coli B ADP-glucose pyrophosphorylase. The Km for alpha-glucose-1-P at saturating to half-saturating concentrations of the activator, fructose-P2, are about the same for both enzymes. However, in the presence of no activator, the concentration of glucose-1-P required for half-maximal activity is about 1.8-fold higher for the SG14 enzyme. Thus SG14 ADP-glucose pyrophosphorylase has lower affinity for its substrates than does the parent enzyme. Previously the SG14 enzyme had been shown to be less sensitive to inhibition by 5'-AMP than the E. coli B enzyme. This ensensitivity to inhibition renders the SG14 enzyme less responsive to energy charge than the E. coli B ADP-glucose pyrophosphorylase. On the basis of the above results and taking into account the reported concentrations of fructose-P2, of pyridoxal-P, and of the adenine nucleotide pool and its energy charge in E. coli strains, it is concluded that furctose-P2 is the important physiological allosteric activator of E. coli ADP-glucose pyrophosphorylase. Furthermore, the 1.7-fold increased rate of accumulation of glycogen observed when E. coli B or SG14 shifts from exponential phase to stationary phase of growth in nitrogen-limiting media can be accounted for by the 2.4-fold increase of the levels of the glycogen biosynthetic enzymes, glycogen synthase, and ADP-glucose pyrophosphorylase. Thus both allosteric regulation of the ADP-glucose pyrophosphorylase as well as the genetic regulation of the biosynthesis of the glycogen biosynthetic enzymes are involved in the regulation of glycogen accumulation in E. coli B.
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PMID:Biosynthesis of bacterial glycogen. Kinetic studies of a glucose-1-phosphate adenylyltransferase (EC 2.7.7.27) from a glycogen-deficient mutant of Escherichia coli B. 24 Aug 34

Inclusion bodies containing glycogen-enzymes were found in 30 to 60% of type 2 fibres of tenotomized calf muscles (m. gastrocnemius, m. soleus, m. plantaris) in rats, using histochemical reactions. The bodies appeared within 1 week after the tenotomy and were localized both in the central and the subsarcolemmal regions and rarely extruded into the extracellular space. These aggregates are 3 to 15 microns in length and 2 to 11 microns in diameter. In addition to glycogen, these bodies also contained various enzymes of the glycogen metabolism such as phosphorylase, a branching enzyme, and glucose-6-phosphatase, but showed no NADH-reductase, lactate dehydrogenase, or myofibrillar ATP-ase activity. The results indicate that glycogen-enzymes containing bodies are a degenerative phenomenon, which occurs only in type 2 fibres of the tenotomized muscles.
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PMID:Glycogen-enzymes containing bodies in type 2 fibres of tenotomized muscles in the rat. 255 27

The replication of a RNA template catalyzed by Q beta replicase was obtained in oleic acid/oleate vesicles simultaneously with the self-reproduction of the vesicles themselves. This was accomplished by entrapping the enzyme Q beta replicase, the RNA template, and the ribonucleotides ATP, CTP, GTP, and UTP inside the vesicles. The water-insoluble oleic anhydride was then added externally. It binds to the vesicle bilayer where it is catalytically hydrolyzed yielding the carboxylate surfactant in situ, which then brings about growth and reproduction of the vesicles themselves. This experiment is presented as a first approach to a synthetic minimal cell, in which the reproduction of the membrane and the replication of the internalized RNA molecules proceed simultaneously.
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PMID:Enzymatic RNA replication in self-reproducing vesicles: an approach to a minimal cell. 753 71

Ketosis, meaning elevation of D-beta-hydroxybutyrate (R-3hydroxybutyrate) and acetoacetate, has been central to starving man's survival by providing nonglucose substrate to his evolutionarily hypertrophied brain, sparing muscle from destruction for glucose synthesis. Surprisingly, D-beta-hydroxybutyrate (abbreviated "betaOHB") may also provide a more efficient source of energy for brain per unit oxygen, supported by the same phenomenon noted in the isolated working perfused rat heart and in sperm. It has also been shown to decrease cell death in two human neuronal cultures, one a model of Alzheimer's and the other of Parkinson's disease. These observations raise the possibility that a number of neurologic disorders, genetic and acquired, might benefit by ketosis. Other beneficial effects from betaOHB include an increased energy of ATP hydrolysis (deltaG') and its linked ionic gradients. This may be significant in drug-resistant epilepsy and in injury and anoxic states. The ability of betaOHB to oxidize co-enzyme Q and reduce NADP+ may also be important in decreasing free radical damage. Clinical maneuvers for increasing blood levels of betaOHB to 2-5 mmol may require synthetic esters or polymers of betaOHB taken orally, probably 100 to 150 g or more daily. This necessitates advances in food-science technology to provide at least enough orally acceptable synthetic material for animal and possibly subsequent clinical testing. The other major need is to bring the technology for the analysis of multiple metabolic "phenotypes" up to the level of sophistication of the instrumentation used, for example, in gene science or in structural biology. This technical strategy will be critical to the characterization of polygenic disorders by enhancing the knowledge gained from gene analysis and from the subsequent steps and modifications of the protein products themselves.
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PMID:Ketone bodies, potential therapeutic uses. 1156 18

Protein phosphorylation in amyloplasts and chloroplasts of Triticum aestivum (wheat) was investigated after the incubation of intact plastids with gamma-(32)P-ATP. Among the soluble phosphoproteins detected in plastids, three forms of starch branching enzyme (SBE) were phosphorylated in amyloplasts (SBEI, SBEIIa, and SBEIIb), and both forms of SBE in chloroplasts (SBEI and SBEIIa) were shown to be phosphorylated after sequencing of the immunoprecipitated (32)P-labeled phosphoproteins using quadrupole-orthogonal acceleration time of flight mass spectrometry. Phosphoamino acid analysis of the phosphorylated SBE forms indicated that the proteins are all phosphorylated on Ser residues. Analysis of starch granule-associated phosphoproteins after incubation of intact amyloplasts with gamma-(32)P-ATP indicated that the granule-associated forms of SBEII and two granule-associated forms of starch synthase (SS) are phosphorylated, including SSIIa. Measurement of SBE activity in amyloplasts and chloroplasts showed that phosphorylation activated SBEIIa (and SBEIIb in amyloplasts), whereas dephosphorylation using alkaline phosphatase reduced the catalytic activity of both enzymes. Phosphorylation and dephosphorylation had no effect on the measurable activity of SBEI in amyloplasts and chloroplasts, and the activities of both granule-bound forms of SBEII in amyloplasts were unaffected by dephosphorylation. Immunoprecipitation experiments using peptide-specific anti-SBE antibodies showed that SBEIIb and starch phosphorylase each coimmunoprecipitated with SBEI in a phosphorylation-dependent manner, suggesting that these enzymes may form protein complexes within the amyloplast in vivo. Conversely, dephosphorylation of immunoprecipitated protein complex led to its disassembly. This article reports direct evidence that enzymes of starch metabolism (amylopectin synthesis) are regulated by protein phosphorylation and indicate a wider role for protein phosphorylation and protein-protein interactions in the control of starch anabolism and catabolism.
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PMID:Protein phosphorylation in amyloplasts regulates starch branching enzyme activity and protein-protein interactions. 1497 70

The intercellular localization of enzymes involved in starch metabolism and the kinetic properties of ADPglucose pyrophosphorylase were studied in mesophyll protoplasts and bundle sheath strands separated by cellulase digestion of Zea mays L. leaves. Activities of starch synthase, branching enzyme, and ADPglucose pyrophosphorylase were higher in the bundle sheath, whereas the degradative enzymes, starch phosphorylase, and amylase were more evenly distributed and slightly higher in the mesophyll. ADPglucose pyrophosphorylase partially purified from the mesophyll and bundle sheath showed similar apparent affinities for Mg(2+), ATP, and glucose-1-phosphate. The pH optimum of the bundle sheath enzyme (7.0-7.8) was lower than that of the mesophyll enzyme (7.8-8.2). The bundle sheath enzyme showed greater activation by 3-phosphoglycerate than did the mesophyll enzyme, and also showed somewhat higher apparent affinity for 3-phosphoglycerate and lower apparent affinity for the inhibitor, orthophosphate. The observed activities of starch metabolism pathway enzymes and the allosteric properties of the ADPglucose pyrophosphorylases appear to favor the synthesis of starch in the bundle sheath while restricting it in the mesophyll.
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PMID:Regulation of Starch Synthesis in the Bundle Sheath and Mesophyll of Zea mays L. : Intercellular Compartmentalization of Enzymes of Starch Metabolism and the Properties of the ADPglucose Pyrophosphorylases. 1666 98

Protein-protein interactions among enzymes of amylopectin biosynthesis were investigated in developing wheat (Triticum aestivum) endosperm. Physical interactions between starch branching enzymes (SBEs) and starch synthases (SSs) were identified from endosperm amyloplasts during the active phase of starch deposition in the developing grain using immunoprecipitation and cross-linking strategies. Coimmunoprecipitation experiments using peptide-specific antibodies indicate that at least two distinct complexes exist containing SSI, SSIIa, and either of SBEIIa or SBEIIb. Chemical cross linking was used to identify protein complexes containing SBEs and SSs from amyloplast extracts. Separation of extracts by gel filtration chromatography demonstrated the presence of SBE and SS forms in protein complexes of around 260 kD and that SBEII forms may also exist as homodimers. Analysis of cross-linked 260-kD aggregation products from amyloplast lysates by mass spectrometry confirmed SSI, SSIIa, and SBEII forms as components of one or more protein complexes in amyloplasts. In vitro phosphorylation experiments with gamma-(32)P-ATP indicated that SSII and both forms of SBEII are phosphorylated. Treatment of the partially purified 260-kD SS-SBE complexes with alkaline phosphatase caused dissociation of the assembly into the respective monomeric proteins, indicating that formation of SS-SBE complexes is phosphorylation dependent. The 260-kD SS-SBEII protein complexes are formed around 10 to 15 d after pollination and were shown to be catalytically active with respect to both SS and SBE activities. Prior to this developmental stage, SSI, SSII, and SBEII forms were detectable only in monomeric form. High molecular weight forms of SBEII demonstrated a higher affinity for in vitro glucan substrates than monomers. These results provide direct evidence for the existence of protein complexes involved in amylopectin biosynthesis.
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PMID:Analysis of protein complexes in wheat amyloplasts reveals functional interactions among starch biosynthetic enzymes. 1826 78

The amylose extender (ae(-)) mutant of maize lacks starch branching enzyme IIb (SBEIIb) activity, resulting in amylopectin with reduced branch point frequency, and longer glucan chains. Recent studies indicate isozymes of soluble starch synthases form high molecular weight complexes with SBEII isoforms. This study investigated the effect of the loss of SBEIIb activity on interactions between starch biosynthetic enzymes in maize endosperm amyloplasts. Results show distinct patterns of protein-protein interactions in amyloplasts of ae(-) mutants compared with the wild type, suggesting functional complementation for loss of SBEIIb by SBEI, SBEIIa, and SP. Coimmunoprecipitation experiments and affinity chromatography using recombinant proteins showed that, in amyloplasts from normal endosperm, protein-protein interactions involving starch synthase I (SSI), SSIIa, and SBEIIb could be detected. By contrast, in ae(-) amyloplasts, SSI and SSIIa interacted with SBEI, SBEIIa, and SP. All interactions in the wild-type were strongly enhanced by ATP, and broken by alkaline phosphatase, indicating a role for protein phosphorylation in their assembly. Whilst ATP and alkaline phosphatase had no effect on the stability of the protein complexes from ae(-) endosperm, radiolabelling experiments showed SP and SBEI were both phosphorylated within the mutant protein complex. It is proposed that, during amylopectin biosynthesis, SSI and SSIIa form the core of a phosphorylation-dependent glucan-synthesizing protein complex which, in normal endosperm, recruits SBEIIb, but when SBEIIb is absent (ae(-)), recruits SBEI, SBEIIa, and SP. Differences in stromal protein complexes are mirrored in the complement of the starch synthesizing enzymes detected in the starch granules of each genotype, reinforcing the hypothesis that the complexes play a functional role in starch biosynthesis.
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PMID:The amylose extender mutant of maize conditions novel protein-protein interactions between starch biosynthetic enzymes in amyloplasts. 1980 95

When oxygen becomes limiting, cells reduce mitochondrial respiration and increase ATP production through anaerobic fermentation of glucose. The Hypoxia Inducible Factors (HIFs) play a key role in this metabolic shift by regulating the transcription of key enzymes of glucose metabolism. Here we show that oxygen regulates the expression of the muscle glycogen synthase (GYS1). Hypoxic GYS1 induction requires HIF activity and a Hypoxia Response Element within its promoter. GYS1 gene induction correlated with a significant increase in glycogen synthase activity and glycogen accumulation in cells exposed to hypoxia. Significantly, knockdown of either HIF1alpha or GYS1 attenuated hypoxia-induced glycogen accumulation, while GYS1 overexpression was sufficient to mimic this effect. Altogether, these results indicate that GYS1 regulation by HIF plays a central role in the hypoxic accumulation of glycogen. Importantly, we found that hypoxia also upregulates the expression of UTP:glucose-1-phosphate urydylyltransferase (UGP2) and 1,4-alpha glucan branching enzyme (GBE1), two enzymes involved in the biosynthesis of glycogen. Therefore, hypoxia regulates almost all the enzymes involved in glycogen metabolism in a coordinated fashion, leading to its accumulation. Finally, we demonstrated that abrogation of glycogen synthesis, by knock-down of GYS1 expression, impairs hypoxic preconditioning, suggesting a physiological role for the glycogen accumulated during chronic hypoxia. In summary, our results uncover a novel effect of hypoxia on glucose metabolism, further supporting the central importance of metabolic reprogramming in the cellular adaptation to hypoxia.
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PMID:Hypoxia promotes glycogen accumulation through hypoxia inducible factor (HIF)-mediated induction of glycogen synthase 1. 2030 Jan 97


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