Home About us Contact
|
Home About us Contact | ||
|
|
||
Sugar Substrates (sugar + substrate)
Selected AbstractsLong-chain 3-hydroxyacyl-CoA dehydrogenase deficiency with inadvertent caries in infantsINTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 1 2007FELIX BLAKE Background., Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare systemic disease that is associated with early tooth decay. Case report., This report describes the case of a 3-year-old boy suffering from LCHADD. At the time of referral, extensive carious lesions of the subject's maxillary dentition necessitated the surgical removal of eight teeth. Preventive treatment for LCHADD involves a regular oral intake of glucose that is vital for the survival of the affected individual. In young infants, the glucose solution needs to be administered as often as every 3 h in order to prevent hypoglycaemia, leading to a local environment similar to that experienced in nursing bottle syndrome. While nursing bottle syndrome can be resolved by eliminating the sugar substrate and curtailing the feeding sessions, these alternatives are not available in cases of LCHADD. Conclusion., This report highlights this rare disease and emphasizes its dire consequences for the dentition. Prophylactic recommendations for high-risk children are reviewed. Familiarity with LCHADD allows this high-risk group of patients to be identified, and thus, ensures diligent prophylactic action. [source] The 1.9,Å resolution structure of Mycobacterium tuberculosis 1-deoxy- d -xylulose 5-phosphate reductoisomerase, a potential drug targetACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2006Lena M. Henriksson 1-Deoxy- d -xylulose 5-phosphate reductoisomerase catalyzes the NADPH-dependent rearrangement and reduction of 1-deoxy- d -xylulose 5-phosphate to form 2- C -methyl- d -erythritol 4-phosphate, as the second step of the deoxyxylulose 5-phosphate/methylerythritol 4-phosphate pathway found in many bacteria and plants. The end product, isopentenyl diphosphate, is the precursor of various isoprenoids vital to all living organisms. The pathway is not found in humans; the mevalonate pathway is instead used for the formation of isopentenyl diphosphate. This difference, combined with its essentiality, makes the reductoisomerase an excellent drug target in a number of pathogenic organisms. The structure of 1-deoxy- d -xylulose 5-phosphate reductoisomerase from Mycobacterium tuberculosis (Rv2870c) was solved by molecular replacement and refined to a resolution of 1.9,Å. The enzyme exhibited an estimated kcat of 5.3,s,1 and Km and kcat/Km values of 7.2,µM and 7.4 × 105,M,1,s,1 for NADPH and 340,µM and 1.6 × 104,M,1,s,1 for 1-deoxy- d -xylulose 5-phosphate. In the structure, a sulfate is bound at the expected site of the phosphate moiety of the sugar substrate. The M. tuberculosis enzyme displays a similar fold to the previously published structures from Escherichia coli and Zymomonas mobilis. Comparisons offer suggestions for the design of specific drugs. Furthermore, the new structure represents an intermediate conformation between the open apo form and the closed holo form observed previously, giving insights into the conformational changes associated with catalysis. [source] A thermostable triple mutant of pyranose 2-oxidase from Trametes multicolor with improved properties for biotechnological applicationsBIOTECHNOLOGY JOURNAL, Issue 4 2009Oliver Spadiut Abstract In order to increase the thermal stability and the catalytic properties of pyranose oxidase (P2Ox) from Trametes multicolor toward its poor substrate D-galactose and the alternative electron acceptor 1,4-benzoquinone (1,4-BQ), we designed the triple-mutant T169G/E542K/V546C. Whereas the wild-type enzyme clearly favors D-glucose as its substrate over D-galactose [substrate selectivity (kcat/KM)Glc/(kcat/KM)Gal = 172], the variant oxidizes both sugars equally well [(kcat/KM)Glc/(kcat/KM)Gal = 0.69], which is of interest for food biotechnology. Furthermore, the variant showed lower KM values and approximately ten-fold higher kcat values for 1,4-BQ when D-galactose was used as the saturating sugar substrate, which makes this enzyme particularly attractive for use in biofuel cells and enzyme-based biosensors. In addition to the altered substrate specificity and reactivity, this mutant also shows significantly improved thermal stability. The half life time at 60°C was approximately 10 h, compared to 7.6 min for the wild-type enzyme. We performed successfully small-scale bioreactor pilot conversion experiments of D -glucose/D -galactose mixtures at both 30 and 50°C, showing the usefulness of this P2Ox variant in biocatalysis as well as the enhanced thermal stability of the enzyme. Moreover, we determined the crystal structure of the mutant in its unligated form at 1.55 Å resolution. Modeling D-galactose in position for oxidation at C2 into the mutant active site shows that substituting Thr for Gly at position 169 favorably accommodates the axial C4 hydroxyl group that would otherwise clash with Thr169 in the wild-type. [source] The linkage between cell wall metabolism and fruit softening: looking to the futureJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 8 2007Ariel R Vicente Abstract The softening that accompanies ripening of commercially important fruits exacerbates damage incurred during shipping and handling and increases pathogen susceptibility. Thus, postharvest biologists have studied fruit softening to identify ways to manage ripening and optimise fruit quality. Studies, generally based on the premise that cell wall polysaccharide breakdown causes ripening-associated softening, have not provided the insights needed to genetically engineer, or selectively breed for, fruits whose softening can be adequately controlled. Herein it is argued that a more holistic view of fruit softening is required. Polysaccharide metabolism is undoubtedly important, but understanding this requires a full appreciation of wall structure and how wall components interact to provide strength. Consideration must be given to wall assembly as well as to wall disassembly. Furthermore, the apoplast must be considered as a developmentally and biochemically distinct, dynamic ,compartment', not just the location of the cell wall structural matrix. New analytical approaches for enhancing the ability to understand wall structure and metabolism are discussed. Fruit cells regulate their turgor pressure as well as cell wall integrity as they ripen, and it is proposed that future studies of fruit softening should include attempts to understand the bases of cell- and tissue-level turgor regulation if the goal of optimising softening control is to be reached. Finally, recent studies show that cell wall breakdown provides sugar substrates that fuel other important cellular pathways and processes. These connections must be explored so that optimisation of softening does not lead to decreases in other aspects of fruit quality. Copyright © 2007 Society of Chemical Industry [source] Leaf respiratory CO2 is 13C-enriched relative to leaf organic components in five species of C3 plantsNEW PHYTOLOGIST, Issue 3 2004Cheng-yuan Xu Summary ,,Here, we compared the carbon isotope ratios of leaf respiratory CO2 (,13CR) and leaf organic components (soluble sugar, water soluble fraction, starch, protein and bulk organic matter) in five C3 plants grown in a glasshouse and inside Biosphere 2. One species, Populus deltoides, was grown under three different CO2 concentrations. ,,The Keeling plot approach was applied to the leaf scale to measure leaf ,13CR and these results were compared with the ,13C of leaf organic components. ,,In all cases, leaf respiratory CO2 was more 13C-enriched than leaf organic components. The amount of 13C enrichment displayed a significant species-specific pattern, but the effect of CO2 treatment was not significant on P. deltoides. ,,In C3 plant leaves, 13C-enriched respiratory CO2 appears widespread. Among currently hypothesized mechanisms contributing to this phenomenon, non-statistical carbon isotope distribution within the sugar substrates seems most likely. However, caution should be taken when attempting to predict the ,13C of leaf respiratory CO2 at the ecosystem scale by upscaling the relationship between leaf ,13CR and ,13C of leaf organic components. [source] An investigation of intracellular glycosylation activities in CHO cells: Effects of nucleotide sugar precursor feedingBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010Niki S.C. Wong Abstract Controlling glycosylation of recombinant proteins produced by CHO cells is highly desired as it can be directed towards maintaining or increasing product quality. To further our understanding of the different factors influencing glycosylation, a glycosylation sub-array of 79 genes and a capillary electrophoresis method which simultaneously analyzes 12 nucleotides and 7 nucleotide sugars; were used to generate intracellular N -glycosylation profiles. Specifically, the effects of nucleotide sugar precursor feeding on intracellular glycosylation activities were analyzed in CHO cells producing recombinant human interferon-, (IFN-,). Galactose (±uridine), glucosamine (±uridine), and N -acetylmannosamine (ManNAc) (±cytidine) feeding resulted in 12%, 28%, and 32% increase in IFN-, sialylation as compared to the untreated control cultures. This could be directly attributed to increases in nucleotide sugar substrates, UDP-Hex (,20-fold), UDP-HexNAc (6- to 15-fold) and CMP-sialic acid (30- to 120-fold), respectively. Up-regulation of B4gal and St3gal could also have enhanced glycan addition onto the proteins, leading to more complete glycosylation (sialylation). Combined feeding of glucosamine,+,uridine and ManNAc,+,cytidine increased UDP-HexNAc and CMP-sialic acid by another two- to fourfold as compared to feeding sugar precursors alone. However, it did not lead to a synergistic increase in IFN-, sialylation. Other factors such as glycosyltransferase or glycan substrate levels could have become limiting. In addition, uridine feeding increased the levels of uridine- and cytidine-activated nucleotide sugars simultaneously, which could imply that uridine is one of the limiting substrates for nucleotide sugar synthesis in the study. Hence, the characterization of intracellular glycosylation activities has increased our understanding of how nucleotide sugar precursor feeding influence glycosylation of recombinant proteins produced in CHO cells. It has also led to the optimization of more effective strategies for manipulating glycan quality. Biotechnol. Bioeng. 2010;107: 321,336. © 2010 Wiley Periodicals, Inc. [source] Probing active-site residues of pyranose 2-oxidase from Trametes multicolor by semi-rational protein designBIOTECHNOLOGY JOURNAL, Issue 4 2009Clara Salaheddin Abstract D -Tagatose is a sweetener with low caloric and non-glycemic characteristics. It can be produced by an enzymatic oxidation of D -galactose specifically at C2 followed by chemical hydrogenation. Pyranose 2-oxidase (P2Ox) from Trametes multicolor catalyzes the oxidation of many aldopyranoses to their corresponding 2-keto derivatives. Since D -galactose is not the preferred substrate of P2Ox, semi-rational design was employed to improve the catalytic efficiency with this poor substrate. Saturation mutagenesis was applied on all positions in the active site of the enzyme, resulting in a library of mutants, which were screened for improved activity in a 96-well microtiter plate format. Mutants with higher activity than wild-type P2Ox were chosen for further kinetic investigations. Variant V546C was found to show a 2.5-fold increase of kcat with both D -glucose and D -galactose when oxygen was used as electron acceptor. Because of weak substrate binding, however, kcat/KM is lower for both sugar substrates compared to wild-type TmP2Ox. Furthermore, variants at position T169, i.e., T169S and T169N, showed an improvement of the catalytic characteristics of P2Ox with D -galactose. Batch conversion experiments of D -galactose to 2-keto- D -galactose were performed with wild-type TmP2O as well as with variants T169S, T169N, V546C and V546C/T169N to corroborate the kinetic properties determined by Michaelis-Menten kinetics. [source] Effects of Various Sugars Added to Growth and Drying Media upon Thermotolerance and Survival throughout Storage of Freeze-Dried lactobacillus delbrueckii ssp. bulgaricusBIOTECHNOLOGY PROGRESS, Issue 1 2004Ana S. Carvalho The aim of this research effort was to investigate the role of various sugar substrates in the growth medium upon thermotolerance and upon survival during storage after freeze-drying of Lactobacillus bulgaricus. Addition of the sugars tested to the growth medium, and of these and sorbitol to the drying medium (skim milk) was investigated so as to determine whether a relationship exists between growth and drying media, in terms of protection of freeze-dried cells throughout storage. The lowest decrease in viability of L. bulgaricuscells after freeze-drying was obtained when that organism was grown in the presence of mannose. However, L. bulgaricusclearly survived better during storage when cells had been grown in the presence of fructose, lactose or mannose rather than glucose (the standard sugar in the growth medium). A similar effect could not be observed in terms of thermotolerance; in this case, the growth medium supplemented with lactose was found to yield cells bearing the highest heat resistance. Supplementation of the drying medium with glucose, fructose, lactose, mannose or sorbitol led in most cases to enhancement of protection during storage, to a degree that was growth medium-dependent. [source] | |||||||||||||