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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)

Neurospora crassa branching enzyme [EC 2.4.1.18] acted on potato amylopectin or amylose to convert them to highly branched glycogen-type molecules which consisted of unit chains of six glucose units. The enzyme also acted on the amylopectin beta-limit dextrin, indicating that the enzyme acted on internal glucose chains as well as outer chains. By the combined action of N. crassa glycogen synthase [EC 2.4.1.11] and the branching enzyme, a glycogen-type molecule was formed from UDP-glucose. In the presence of primer glycogen, the glucose transfer reaction was accelerated by the addition of branching enzyme. On the other hand, the glucose transfer reaction by glycogen synthase did not occur without primers. When the branching enzyme was added, the glucose transfer occurred after a short time lag. This recovery of the glucose transfer reaction did not occur upon addition of the inactivated branching enzyme. The structure of the product formed by the combined action of the two enzymes was different from that of the intact N. crassa glycogen with respect to the distribution patterns of the unit chains.
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PMID:Mode of action of glycogen branching enzyme from Neurospora crassa. 213 54

The interaction of Neurospora crassa branching enzyme (1,4-alpha-D-glucan:1,4-alpha-D-glucan 6-alpha-(1,4-alpha-glucano)-transferase) [EC 2.4.1.18] with substrate glycogen or amylopectin was studied by affinity electrophoresis. By this method, the dissociation constants (K) of the branching enzyme for oyster glycogen (CL-12.2, OCL-6.3) and for potato amylopectin (CL-20, OCL-12.8) were determined to be 13.3 mM and 0.355 mM, respectively. The affinity of the enzyme to the substrate glycogen increased with the increase of outer chain length (OCL) of the substrate. The thermodynamic parameters of the branching reaction were obtained from the changes of K values of the enzyme-substrate complex at various temperatures. The value of heat change (delta H degree) of the branching reaction for amylopectin was -27.7 kcal/deg.mol. The most suitable length of glucan chain for branching was greater than 12 glucose units.
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PMID:A kinetic study of the interaction between glycogen and Neurospora crassa branching enzyme. 213 55

Glycogen synthesis in rabbit muscle takes place on an autocatalytic protein that glucosylates itself to form a maltosaccharide that in turn primes the actions of glycogen synthase and branching enzyme to form glycogen. Here we show that in the form in which the protein is isolated from muscle it already contains one molecular proportion of a maltosaccharide ranging in length from 2 to 8 glucose residues. Self-glucosylation consists in the lengthening of all the chains to become malto-octaose.
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PMID:The biogenesis of glycogen: nature of the carbohydrate in the protein primer. 240 65

In this paper we elucidate part of the mechanism of the early stages of the biosynthesis of glycogen. This macromolecule is constructed by covalent apposition of glucose units to a protein, glycogenin, which remains covalently attached to the mature glycogen molecule. We have now isolated, in a 3500-fold purification, a protein from rabbit muscle that has the same Mr as glycogenin, is immunologically similar, and proves to be a self-glucosylating protein (SGP). When incubated with UDP-[14C]glucose, an average of one molecular proportion of glucose is incorporated into the protein, which we conclude is the same as glycogenin isolated from native glycogen. The native SGP appears to exist as a high-molecular-weight species that contains many identical subunits. Because the glucose that is self-incorporated can be released almost completely from the acceptor by glycogenolytic enzymes, the indication is that it was added to a preformed chain or chains of 1,4-linked alpha-glucose residues. This implies that SGP already carries an existing maltosaccharide chain or chains to which the glucose is added, rather than glucose being added directly to protein. The putative role of SGP in glycogen synthesis is confirmed by the fact that glucosylated SGP acts as a primer for glycogen synthase and branching enzyme to form high-molecular-weight material. SGP itself is completely free from glycogen synthase. The quantity of SGP in muscle is calculated to be about one-half the amount of glycogenin bound in glycogen.
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PMID:A self-glucosylating protein is the primer for rabbit muscle glycogen biosynthesis. 297 23

Methods previously described for glycogen or amylopectin branching enzymatic activity are insufficiently sensitive and not quantitative. A new, more sensitive, specific, and quantitative one was developed. It is based upon the quantitation of the glucose residues joined by alpha 1,6 bonds introduced by varying amounts of branching enzyme. The procedure involved the synthesis of a polysaccharide from Glc-1-P and phosphorylase in the presence of the sample to be tested. The branched polysaccharide was then purified and the glucoses involved in the branching points were quantitated after degradation with phosphorylase and debranching enzymes. This method appeared to be useful, not only in enzymatic activity determinations but also in the study of the structure of alpha-D-glucans when combined with those of total polysaccharide quantitation, such as iodine and phenol-sulfuric acid.
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PMID:Branching enzyme assay: selective quantitation of the alpha 1,6-linked glucosyl residues involved in the branching points. 316 Feb 57

The mechanism of action of liver branching enzyme has been studied by using as substrate two polysaccharides in which the non-reducing ends had been labelled by incubation with phosphorylase and a trace amount of [(14)C]glucose 1-phosphate. After these polysaccharides had been treated with branching enzyme, their structure was analysed by periodate oxidation, by degradation with phosphorylase and amylo-(1-->6)-glucosidase and by degradation with pullulanase. All the results indicate that the branching enzyme catalyses the transfer from (1-->4)- to (1-->6)-linkage of a chain of glucose units, the minimum length of which is six glucose units. A maltodextrin containing 16 glucose units was not acted on by the branching enzyme.
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PMID:A study of the reaction catalysed by the liver branching enzyme. 429 May 51

1. Pullulanase synthesis was studied in 16 classified (N.C.I.B.) strains and in an industrial strain (R) of Klebsiella aerogenes grown in chemostats containing maltose as inducer and sole carbon source. 2. Maximum synthesis was associated with carbon-limited growth at a low dilution rate (about 0.2h(-1)). The enzyme remained firmly cell-bound and seemed to be located on the cell surface. 3. Three strains had high activity (R, N.C.I.B. 5938, 8017), twelve were intermediate, and two (N.C.I.B. 8153, 9146) had negligible activity but were inducible with pullulan. 4. Pullulan similarly induced low, but adequate, activity in the other strains in conditions (nutrient limitation other than carbon-limitation) in which pullulanase was otherwise very seriously repressed. Nevertheless, in carbon limitation pullulan induced no more enzyme than did maltose, maltotriose or oligosaccharide mixtures, and ;hyperactivity' never developed on protracted culture. 5. Cyclic AMP relieved the transient repression produced by adding glucose to maltose-limited cultures and a further change to glucose-limited conditions led to constitutive pullulanase synthesis. 6. Amylomaltase and alpha-glucosidase activities were also examined but in less detail. 7. The presence of pullulanase in maltose-limited growth is discussed, but no clear function can be assigned to it at present. The molar growth yields for all the strains were very similar, and no correlation was found between the overgrowth of one strain by another and pullulanase activity. Further, any function as a general branching enzyme in polysaccharide synthesis seems unlikely.
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PMID:Pullulanase synthesis in klebsiella (aerobacter) aerogenes strains growing in continuous culture. 437 62

Human skin fibroblasts from patients with Type IV glycogen storage disease, in which there is a demonstrable deficiency of glycogen branching enzyme, were shown to be able to synthesize [14C]glycogen containing [14C]glucose at branch points when sonicates containing endogenous glycogen synthase a were incubated with UDP[14C]glucose. The branch point content of the glycogen synthesized by the Type IV cells was essentially the same as that formed by normal cells, but the total synthetic capacity of the Type IV cells was lower. A new assay for the branching enzyme using glycogen synthase as the indicator enzyme has been developed. Using this assay it has been shown that the residual branching enzyme of affected children and of their heterozygote parents is less easily inhibited by an IgG antibody raised in rabbits against the normal human liver enzyme than is the branching enzyme of normal fibroblasts.
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PMID:Studies of the residual glycogen branching enzyme activity present in human skin fibroblasts from patients with type IV glycogen storage disease. 622 Jul 6

Polyglucose particles histochemically synthesized from glucose 1-phosphate by phosphorylase and branching glycosyltransferase were observed in the gastric carcinoma cells, in intestinal metaplastic epithelium of the gastric mucosa and in fetal epithelium of the fetal gastric mucosa by light and electron microscopical studies. Light microscopical observations resembled those in previous reports. As for the electron microscopical observations, in gastric carcinoma cells, the polyglucaose synthesizing area were expansively widened by a deposition of synthesized polyglucose particles. Three patterns of their intracellular distribution, (Focal type, scattered type and singly deposited type) were observed. Besides, two types of polyglucose particle were synthesized. One type appeared as monoparticles which were relatively similar in size and the other type appeared as rosette-like structures which varied in size. Larger polyglucose particles which resembled the polyglucose particle synthesized in the fetal epithelium were observed among them. In the intestinal metaplastic epithelium, polyglucose particles which were similar in size were synthesized in narrow focal areas of the cytoplasmic matrix. The distribution, shape and size of polyglucose particles synthesized in the carcinoma cells were irregular as compared with those in the intestinal metaplastic elpithelium. It seems that these irregularities were due to the influence of enzymne deviation caused by carcinoma.
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PMID:Histochemical observations of polyglucose synthesized by enzyme activities in human gastric carcinoma. 644 38

In the diagnosis of metabolic myopathies the use of biochemical methods, in addition to morphological examination of muscle biopsies, is often necessary in order to identify a specific metabolic defect. In order to narrow down the spectrum of biochemical methods, extensive clinical investigation and morphological examination, including histology, enzyme histochemistry and electromicroscopy if necessary have to be done beforehand. Patients are classified in the following groups: 1) progressive muscular weakness and/or muscle wasting with storage of a) glycogen, b) lipid or c) mitochondrial alterations; 2) recurrent rhabdomyolysis induced by fasting or exercise a) with glycogen storage or b) without any specific morphological alterations. The spectrum of metabolic defects comprises disorders of glycogen and glucose metabolism (deficiency of acid maltase, debranching and branching enzyme, phosphorylase, phosphofructokinase and other glycolytic enzymes), lipid metabolism (carnitine deficiency, carnitine palmitoyl transferase deficiency), mitochondria (respiratory chain disorders, pyruvate dehydrogenase deficiency) and others such as adenylate deaminase deficiency. In some of these e.g. infantile acid maltase deficiency and mitochondriopathies, it is clinically more important when organs other than muscle are affected; however, muscle biopsy is a useful substrate for diagnosis of these metabolic disorders.
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PMID:[Diagnostic significance of muscle biopsies in metabolic myopathies. II. Clinical biochemistry]. 659 Sep 24


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