No description available.

No / The first report of the formation of an acetyl disulfide sialoside during the synthesis of thioglycosides is described. This compound is a by-product in the synthesis of the 2-thioacetyl sialoside commonly used in thioglycoside preparation. Our investigations into the identification of this novel disulfide are described.

Yes / The disulfide bond plays an important role in the formation and stabilisation of higher order structures of peptides and proteins, while in recent years interest in this functional group has been extended to carbohydrate chemistry. Rarely found in nature, glycosyl disulfides have attracted significant attention as glycomimetics, with wide biological applications including lectin binding, as key components of dynamic libraries to study carbohydrate structures, the study of metabolic and enzymatic studies, and even as potential drug molecules. This interest has been accompanied and fuelled by the continuous development of new methods to construct the disulfide bond at the anomeric centre. Glycosyl disulfides have also been exploited as versatile intermediates in carbohydrate synthesis, particularly as glycosyl donors. This review focuses on the importance of the disulfide bond in glycobiology and in chemistry, evaluating the different methods available to synthesise glycosyl disulfides. Furthermore, we review the role of glycosyl disulfides as intermediates and/or glycosyl donors for the synthesis of neoglycoproteins and oligosaccharides, before finally considering examples of how this important class of carbohydrates have made an impact in biological and therapeutic contexts. / The authors thank the Institute of Cancer Therapeutics (University of Bradford) Doctoral Training Centre for financial support.

The purpose of this thesis is to explore the nonlinear refractive index of carbon disulfide vapors as opposed to its liquid form. With CS[sub2] vapors, the vapors are less dense so they will rotate longer than liquid CS[sub2] because there are less intermolecular interactions. The electric field of the beam causes the molecules to align with the electric field and applies a torque to the molecules. After this excitation, the molecules continue rotating. The rotations change the index of refraction of the material. Continuous rotation of the molecules causes the index of refraction to be periodic which means the molecules are going through multiple revivals. I will analyze this periodic nonlinear index of refraction. However, some problems occurred while the experiment was being done as well as some issues of measuring CS[sub2] because of white light continuum generation in the cell walls. To avoid these issues we measured the air in the lab and were able to observe the periodic change of index of refraction for O[sub2] and N[sub2].

No description available.

No description available.

M.S.

<p>Members of the thioredoxin superfamily of proteins catalyze disulfide bond reduction and oxidation using the active site C-X-X-C sequence. In hyperthermophilic organisms, cysteine side chains were expected in low abundance since they were not believed to endure the high temperatures under which they grow. Recently it has been found that disulfide bonds in hyperthermophiles are more frequent, the higher the growth temperature of the organism. This is perhaps used as an adaptation to high temperature in order to stabilize proteins under harsh conditions. A protein with sequence and structural similarities to mesophilic members of the thioredoxin superfamily, called protein disulfide oxidoreductases (PDO), has been found in the genomes of recently sequenced hyperthermophilic genomes. In this study PDOs from the hyperthermophiles Aquifex aeolicus (AaPDO) and Pyrococcus furiosus (PfPDO) have been investigated. The molecular weight is about 26 kDa and their structures are comprised of two homologous thioredoxin folds, referred to as the N-unit and the C-unit, each containing a C-X-X-C motif. The sequence identity between the two units and the two proteins is low, but they are still structurally very similar. The function of these proteins in vivo is unknown. As a first step in characterizing the activity of these proteins, the redox characteristics of these domains will be investigated. During this project, the genes for AaPDO and PfPDO have been cloned into overexpression vectors, expressed in E. coli and purified to homogeneity. To allow for individual study of the activities of two units, mutated proteins were prepared in which the cysteine residues of the N-unit (AaPDOnm and PfPDOnm) and of the C-unit (AaPDOcm and PfPDOcm) and purified. Circular dichroism spectra recorded of the wild type and mutants indicate that all purified proteins are folded and that the N- and C-unit active site mutants are structurally similar to the corresponding wild type proteins.</p>

Members of the thioredoxin superfamily of proteins catalyze disulfide bond reduction and oxidation using the active site C-X-X-C sequence. In hyperthermophilic organisms, cysteine side chains were expected in low abundance since they were not believed to endure the high temperatures under which they grow. Recently it has been found that disulfide bonds in hyperthermophiles are more frequent, the higher the growth temperature of the organism. This is perhaps used as an adaptation to high temperature in order to stabilize proteins under harsh conditions. A protein with sequence and structural similarities to mesophilic members of the thioredoxin superfamily, called protein disulfide oxidoreductases (PDO), has been found in the genomes of recently sequenced hyperthermophilic genomes. In this study PDOs from the hyperthermophiles Aquifex aeolicus (AaPDO) and Pyrococcus furiosus (PfPDO) have been investigated. The molecular weight is about 26 kDa and their structures are comprised of two homologous thioredoxin folds, referred to as the N-unit and the C-unit, each containing a C-X-X-C motif. The sequence identity between the two units and the two proteins is low, but they are still structurally very similar. The function of these proteins in vivo is unknown. As a first step in characterizing the activity of these proteins, the redox characteristics of these domains will be investigated. During this project, the genes for AaPDO and PfPDO have been cloned into overexpression vectors, expressed in E. coli and purified to homogeneity. To allow for individual study of the activities of two units, mutated proteins were prepared in which the cysteine residues of the N-unit (AaPDOnm and PfPDOnm) and of the C-unit (AaPDOcm and PfPDOcm) and purified. Circular dichroism spectra recorded of the wild type and mutants indicate that all purified proteins are folded and that the N- and C-unit active site mutants are structurally similar to the corresponding wild type proteins.

Protein disulfide isomerases (PDIs) catalyze the oxidation and isomerization of disulfide bonds in proteins passing through the endoplasmic reticulum (ER). Although as many as 20 enzymes are classified as PDI family members, their relative contributions to protein folding have remained an open question. Additionally, Ero1 has been characterized as the ER oxidase that transfers oxidizing equivalents from oxygen to PDI enzymes. However, knockout mice lacking the mammalian Ero1 isoforms, Ero1Lα and Ero1Lβ, are viable, and the role of other potential ER oxidases in maintaining an oxidative ER environment is now an important issue. By systematic depletion of ER PDI family members and potential ER oxidases and assessment of disulfide bond formation of secreted endogenous substrates, I have outlined the functional relationships among some of these enzymes. PDI family member depletion revealed that PDI, although not essential for complete disulfide bond formation in client proteins, is the most significant catalyst of oxidative folding. In comparison, ERp57 acts preferentially on glycosylated substrates, ERp72 functions in a more supplementary capacity, and P5 has no detectable role in formation of disulfide bonds for the substrates assayed. Initially, no impact of depletion of Ero1 was observed under steady state conditions, suggesting that other oxidase systems are working in parallel to support normal disulfide bond formation. Subsequent experiments incorporating a reductive challenge revealed that Ero1 depletion produces the strongest delay in re-oxidation of the ER and oxidation of substrate. Depletion of two other potential ER oxidases, peroxiredoxin 4 (PRDX4) and Vitamin K epoxide reductase (VKOR), showed more modest effects. Upon co-depletion of Ero1 and other oxidases, additive effects were observed, culminating in cell death following combined removal of Ero1, PRDX4, and VKOR activities. These studies affirm the predominant roles of Ero1 in ER oxidation processes and, for the first time, establish VKOR as a significant contributor to disulfide bond formation.