Detection of secondary structure in glycosaminoglycans via the H n.m.r. signal of the acetamido NH group.

Two simple methods for dissolving salts of acid glycosaminoglycans with inorganic cations (e.g. Li+ and Na+) in dry dimethyl sulphoxide are described. Complete n.m.r. spectra of, e.g., Na+ and Li+ salts of chondroitin sulphate and keratan sulphate were obtained on these solutions. In [2H6]dimethyl sulphoxide the NH resonance of 2-acetamido-2-deoxy hexosides is in the range 7.2-8.0 delta, but is downfield (8.3-9.3 delta) when the NH is H-bonded to -CO2-. Heparan sulphate shows two NH resonances, of which one (at 8.3 delta) is probably indicative of H-bonding. Space-filling models show that a very close approach of NH to -CO2- across the alpha-glucosaminidic bond is possible, and a solution configuration for heparan sulphate is proposed. The n.m.r. results are entirely compatible with interpretations of periodate-oxidation kinetics, based on H-bonded secondary structures present in hyaluronate and chondroitin sulphates, but not in dermatan (or keratan) sulphate.     

Nuclear magnetic resonance studies on a cyclic dodecapeptide analogue of a repeat hexapeptide of tropoelastin: evaluation of secondary structure.

The cyclododecapeptide, (Ala1-Pro2-Gly3-Val4-Gly5-Val6)2, was synthesized and its secondary structure was evaluated from extensive studies in dimethyl sulphoxide, trifluoroethanol and water using NMR methods. A selective decoupling technique in 13C-NMR has been utilized in order to assign the C=O carbon resonances. Temperature dependence of the peptide NH protons and the solvent perturbation of the peptide NH and C=O resonances show the occurrence in all solvents of a beta-turn (a 10-membered H-bond between the Val4 NH and Ala1 C=O) and a gamma-turn, an 11-membered H-bond between the Gly3 NH and the Gly5 C=O; and a possible 14-membered H-bond between the Ala1 NH and the Val4 C=O in dimethyl sulphoxide and trifluoroethanol. These secondary structural features are compared with the linear polyhexapeptide and found the the beta-turn and the gamma-turn are the common conformational features of these peptide systems.     

Dimethyl sulphoxide: A review of its applications in cell biology

Dimethyl sulphoxide is a water miscible solvent that has wide applications in cell biology. It acts as a cryoprotective agent in a variety of cells and tissues allowing prolonged storage at subzero temperatures. The action of dimethyl sulphoxide on the stability of the liquid matrix of cell membranes appears to be responsible for its effects and this appears also to be true for related effects on membrane permeability and fusion. Dimethyl sulphoxide is also known to act as an inducer of cellular differentiation and as a free radical scavenger and radioprotectant. A review of the underlying molecular basis of all these effects of dimethyl sulphoxide is presented.     

Effect of dimethyl sulphoxide on the crystal structure of porcine pepsin

The structure of porcine pepsin crystallized in the presence of dimethyl sulphoxide has been analysed by X-ray crystallography to obtain insights into the structural events that occur at the onset of chemical denaturation of proteins. The results show that one dimethyl sulphoxide molecule occupies a site on the surface of pepsin interacting with two of its residues. An increase in the average temperature factor of pepsin in the presence of dimethyl sulphoxide has been observed indicating protein destabilization induced by the denaturant. Significant increase in the temperature factor and weakening of the electron density have been observed for the catalytic water molecule located between the active aspartates. The conformation of pepsin remains unchanged in the crystal structure. However, the enzyme assay and circular dichroism studies indicate that dimethyl sulphoxide causes a slight change in the secondary structure and complete loss of activity of pepsin in solution.     

The modulation of membrane structure and stability by dimethyl sulphoxide (Review)

Dimethyl sulphoxide is a widely used agent in cell biology. It is well known as a cryoprotectant, cell fusogen and a permeability enhancing agent. These applications depend, to a greater or lesser extent, on the effect of dimethyl sulphoxide on the stability and dynamics of biomembranes. The aim of this review is to examine progress of the research which has been directed towards studies of the interactions between dimethyl sulphoxide and membranes, particularly that with the lipid components of cell membranes, as seen in its effects on model membrane systems. Models are proposed to explain the mechanism whereby dimethyl sulphoxide may mediate its effects on biological functions by its effects on the stability and properties of the membrane lipid matrix.     

Solution structures of ferrihaem in some dipolar aprotic solvents and their binary aqueous mixtures

1. Conductivity and u.v. and visible spectroscopic techniques were used to investigate the solution structure of the prosthetic group of the ferric haemoproteins (ferrihaem) in dimethyl sulphoxide, NN-dimethylacetamide, NN-dimethylformamide and sulpholane, and certain of their aqueous mixtures. 2. In neutral or acid dimethyl sulphoxide, chlorohaemin is monomeric and completely dissociated into Cl⁻ion and a ferrihaem species with dimethyl sulphoxide molecules in the fifth and sixth co-ordination positions on iron. 3. In neutral NN-dimethylacetamide and NN-dimethylformamide chlorohaemin is monomeric but is largely undissociated, giving different spectra from that of chlorohaemin in dimethyl sulphoxide. On acidification, dissociation occurs and the dimethyl sulphoxide type of spectrum results. 4. Studies in a fourth solvent, sulpholane, indicate that solvent co-ordinating power (ligand strength) rather than bulk dielectric constant is responsible for dissociation of chlorohaemin. 5. In neutral dimethyl sulphoxide–water mixtures chlorohaemin remains monomeric and completely dissociated, and spectra are independent of mixture composition, except at high water concentrations, when precipitation occurs. In alkaline dimethyl sulphoxide–water mixtures, where the complete solvent mixture range is accessible, ferrihaem is polymeric (probably dimeric) and spectra are dependent on solvent composition. A quantitative analysis indicates that the spectral changes are due to replacement by water of one molecule of co-ordinated dimethyl sulphoxide per ferrihaem aggregate, and do not involve a two-molecule replacement as has been suggested for the alkaline pyridine–water system.     

Studies on horseradish peroxidase in dimethyl sulphoxide/water mixtures. The activation of hydrogen peroxide and the binding of fluoride.

We studied the variation in spectra and in reactivity towards H2O2 of solutions of horseradish peroxidase in dimethyl sulphoxide/water mixtures, obtained by diluting stock solutions of the enzyme in either water or dimethyl sulphoxide, and assayed the enzyme activity and studied the binding of F- by the peroxidase in 65% (v/v) dimethyl sulphoxide. A broadly similar pattern of changes is observed whether one starts from water or from dimethyl sulphoxide; the changes are essentially reversible, though hysteresis is observed. When the dimethyl sulphoxide content of the solvent mixture is increased, the peroxidase retains its ability to activate H2O2 up to 74% (v/v) dimethyl sulphoxide. The peroxidase in 65% (v/v) dimethyl sulphoxide binds F- together with a proton (or the equivalent loss of HO-), as already established for aqueous solutions. We point out that the occurrence in such solutions of both the ability to activate H2O2 and the inability to bind F- without taking up H+ or losing HO- supports the proposed mechanism for activating H202, whereby the protein binds the substrate in the form of the much more reactive HO2-.     

Secondary structures of hyaluronate and chondroitin sulphates. A 1H n.m.r. study of NH signals in dimethyl sulphoxide solution.

1H n.m.r. spectra in [2H6]dimethyl sulphoxide of dodecyltrimethylammonium salts of chondroitin sulphates and hyaluronate, or sodium salts of oligomers from hyaluronate, showed unambiguous NH signals. The acetamido NH occurs in two different environments: environment I ('normal') in simple sugars, and environment II (hydrogen-bonded NH) appearing in tri- or tetrasaccharides, indicating a secondary structure in hyaluronate (and some chondroitin sulphates) involving a hydrogen-bonded acetamido NH.     

Stabilization of Na+, K+-adenosine triphosphatase by dimethyl sulfoxide under inactivation by urea]

Hydrophobic agents, e.g. methanol, ethanol, isopropanol, acetone and dioxane were shown to induce irreversible inactivation of Na+, K+-adenosine triphosphatase beginning with their concentrations of 20 to 35%, whereas dimethyl sulphoxide exerted similar effect only at concentration of 50% and higher. Urea also irreversibly inactivated Na+, K+-adenosine triphosphatase, beginning with a concentration of about 20%. It was found that, dimethyl sulphoxide contrary to the other hydrophobic agents studied, protected Na+, K+-adenosine triphosphatase against the inactivating (denaturing) action of urea. The highest stabilizing effect of dimethyl sulphoxide was displayed at concentrations from 20 to 30%.     

Rheology and microstructure of solutions of the microbial polysaccharide from Pseudomonas elodea

Rheological studies of solutions and gels of the microbial polysaccharide from the organism Pseudomonas elodea have been combined with X-ray diffraction studies of fibres and pulsed electric-birefringence studies of dilute solutions, to investigate the conformation and interaction of the polymer molecules. Rheological data are suggestive of a locally rigid conformation for the biopolymer in solution. X-Ray diffraction studies suggest that the molecules adopt a three-fold helical structure. O-Acetyl substituents have been shown to inhibit the packing of these helices into crystalline domains. Studies of pulsed electric-birefringence suggest an extended, kinetically rigid structure in solution. Dissolving the polysaccharide in dimethyl sulphoxide inhibits the gelation and shear-thinning characteristics of aqueous solutions. Comparative studies of electric birefringence of solutions in water and dimethyl sulphoxide suggest that the differences in rheological properties may result from a change in molecular conformation.     

Flow cytometry is a new method for the characterization of intestinal plasma membrane.

The highly differentiated plasma membrane of rabbit enterocytes constitutes an interesting model for membrane studies. Flow cytometry allows combined measurements of the size of membrane vesicles by light-scatter and fluorescence polarization at a single-particle level. The degree of fluorescence polarization of 1,6-diphenylhexa-1,3,5-triene was determined at 4, 18 and 37 degrees C in the brush-border and basolateral plasma membranes. The fluorescence polarization was considerably higher in brush-border than in basolateral membranes. After incubation with dimethyl sulphoxide, the membrane fluidity decreased in both types of membranes. Moreover, a time-effect study of dimethyl sulphoxide showed changes in fluorescence polarization. Only in brush-border membrane a temporary fluid phase was observed. The different properties of the two membrane domains in relation to the lipid-protein dynamics of enterocytes are discussed.     

The exchange of unesterified cholesterol between human low-density lipoproteins and rat erythrocyte `ghosts''

1. The exchange of unesterified cholesterol molecules between rat erythrocyte ;ghosts' and human low-density lipoproteins has been studied under a number of different experimental conditions. 2. The process is pH-dependent, the rate being minimal at about pH5. 3. Cholesterol exchange does not vary greatly with temperature, the rate at 50 degrees being less than twice that at 2 degrees . 4. Large variations in the ionic strength or Ca(2+) concentration of the medium have little effect, but the exchange rate is greatly increased in the presence of a wide range of chemical compounds, e.g. urea, alcohols, acetone, dimethyl sulphoxide and tetra-alkyl-ammonium salts. 5. Acetone and dimethyl sulphoxide have a much greater effect at 37 degrees than at 8-10 degrees . 6. It is proposed that hydrophobic bonding is of great importance in maintaining the structure of ;ghosts' and lipoproteins. 7. The results are discussed in relation to current theories of membrane and lipoprotein structure.     

Studies of the conformation of bilirubin and its dimethyl ester in dimethyl sulphoxide solutions by nuclear magnetic resonance.

The conformation of bilirubin and its dimethyl ester in dimethyl sulphoxide (DMSO) was investigated by n.m.r. spectroscopy. The chemical shifts of the pyrrole NH and Lactam protons of bilirubin and its dimethyl ester in DMSO indicate a strong interaction with the solvent. Inter-proton distances were calculated from nuclear Overhauser effects (NOE), selective and non-selective relaxation times (T1) and rotational correlation times taken from 13C relaxation times. The interproton distances indicate that the conformation of the skeleton of bilirubin and its dimethyl ester in DMSO is similar to that of bilirubin and mesobilirubin in the crystalline state and in chloroform solutions, except for a possible slight twist of the pyrrolenone rings about the methine bonds, which may be a consequence of solvation of the NH groups by DMSO. Unlike in chloroform solutions, no direct hydrogen-bonding occurs between the carboxylic acid and the lactam groups of bilirubin in DMSO, as shown by the absence of an NOE between these groups. The fast exchange of the pyrrole NH protons with 2H shows that no hydrogen-bonding occurs between these protons and the propionic residues, in line with their solvation by DMSO. From the above results, and from the slowness of the internal motion of the propionic residues of bilirubin and its dimethyl ester, it is concluded that these residues are tied to the skeleton via bound solvent molecules.     

Studies on haemin in dimethyl sulphoxide/water mixtures.

The nature of the complexes and equilibria shown by solutions of protohaemin in dimethyl sulphoxide/water mixtures and in the presence of acid and base were studied by u.v.-visible spectrophotometry. In neutral solutions containing from 40 to 100% dimethyl sulphoxide, haemin is present as a monomeric complex in which the Cl-ion is not coordinated. Only a single pH-dependent equilibrium pK12 is observed over the range 40-80% dimethylsulphoxide, corresponding to formation of the mu-oxo dimer. As the dimethyl sulphoxide content is lowered below 35%, so the single equilibrium (pK12) is replaced by two equilibria (pK1 and pK2); with solutions of 5 microM-haemin, pK1 decreases (from pK12 7.55 in 65% dimethyl sulphoxide to pK1 approx. 1.5 in 0.01% dimethyl sulphoxide), whereas pK2 hardly changes (from pK12 7.55 in 65% to pK2 approx. 7.5 in 0.01%).     

Fatty acid utilization during development of the rat

The effects of dimethyl sulphoxide and glycerol on ox brain microsomal Na(+)+K(+)-stimulated adenosine triphosphatase (EC 3.6.1.3), K(+)-stimulated p-nitrophenyl phosphatase and K(+)-dependent muscle pyruvate kinase (EC 2.7.1.40) were studied. Dimethyl sulphoxide at concentrations below 20% (v/v) was found to stimulate the p-nitrophenyl phosphatase and pyruvate kinase by increasing their affinity for K(+) but to inhibit the Na(+)+K(+)-stimulated adenosine triphosphatase. The latter enzyme activity was also inhibited by glycerol, which like dimethyl sulphoxide, stimulated the K(+)-activated p-nitrophenyl phosphatase at a wide range of concentrations. The solvent effects were promptly reversed by dilution. Similarity was found between glycerol and dimethyl sulphoxide, on one hand, and ATP, on the other, in their stimulatory effect and their ability to increase the ouabain- and oligomycin-sensitivity of the K(+)-stimulated p-nitrophenyl phosphatase. However, only the solvents, not the ATP, increased the binding of K(+) by the microsomes. From the above findings it is suggested that solvents may act on K(+)-dependent enzymes by altering the state of solvation of the activating cation as well as by changing the enzyme structure.     

The hyaluronan receptor (CD44) participates in the uptake and degradation of hyaluronan

The hyaluronan receptor belongs to the polymorphic family of CD44 glycoproteins, which have been implicated in a variety of cellular functions including adhesion to hyaluronan and collagen, the binding of lymphocytes to high endothelial cells during extravasation, and conferring metastatic potential to carcinoma cells. Here, we demonstrate that the receptor also participates in the uptake and degradation of hyaluronan by both transformed fibroblasts (SV-3T3 cells) and alveolar macrophages. These cells were incubated with isotopically labeled hyaluronan for various periods of time, and the extent of degradation was determined by either molecular-sieve chromatography or centrifugation through Centricon 30 microconcentrators. The macrophages degraded the hyaluronan at a faster rate than the SV-3T3 cells, which may reflect the fact that they contained a greater number of receptors. More importantly, in both cell types, the degradation of hyaluronan was specifically blocked by antibodies directed against the receptor. However, the receptor by itself did not have the ability to degrade hyaluronan, since preparations of SV-3T3 membranes containing the receptor did not break down hyaluronan. Subsequent experiments revealed that macrophages can internalize fluorescein-tagged hyaluronan, and this process was blocked by antibodies against the receptor. Furthermore, the subsequent degradation of hyaluronan was inhibited by agents that block the acidification of lysosomes (chloroquine and NH4Cl). Thus, the most likely explanation for these results is that the receptor mediates the uptake of hyaluronan into the cell where it can be degraded by acid hydrolases in lysosomes. The ability of cells expressing the receptor to degrade hyaluronan may be important during tissue morphogenesis and cell migration.     

Bupivacaine hydrochloride induces muscle fiber necrosis and hydroxyl radical formation-dimethyl sulphoxide reduces hydroxyl radical formation

We induced acute skeletal muscle necrosis in rats using bupivacaine hydrochloride and found that both 2,5- and 2,3-dihydroxybenzoic acid significantly increased in skeletal muscle. A single administration of dimethyl sulphoxide, a free radical scavenger, significantly lowered concentrations of 2,5- and 2,3-dihydroxybenzoic acid. These results suggest that dimethyl sulphoxide is an effective hydroxyl radical scavenger and may be useful in the treatment of myopathy.     

TSG-6 protein binding to glycosaminoglycans: formation of stable complexes with hyaluronan and binding to chondroitin sulfates

TSG-6 protein, up-regulated in inflammatory lesions and in the ovary during ovulation, shows anti-inflammatory activity and plays an essential role in female fertility. Studies in murine models of acute inflammation and experimental arthritis demonstrated that TSG-6 has a strong anti-inflammatory and chondroprotective effect. TSG-6 protein is composed of the N-terminal link module that binds hyaluronan and a C-terminal CUB domain, present in a variety of proteins. Interactions between the isolated link module and hyaluronan have been studied extensively, but little is known about the binding of full-length TSG-6 protein to hyaluronan and other glycosaminoglycans. We show that TSG-6 protein and hyaluronan, in a temperature-dependent fashion, form a stable complex that is resistant to dissociating agents. The formation of such stable complexes may underlie the activities of TSG-6 protein in inflammation and fertility, e.g. the TSG-6-dependent cross-linking of hyaluronan in the cumulus cell-oocyte complex during ovulation. Because adhesion to hyaluronan is involved in cell trafficking in inflammatory processes, we also studied the effect of TSG-6 on cell adhesion. TSG-6 binding to immobilized hyaluronan did not interfere with subsequent adhesion of lymphoid cells. In addition to immobilized hyaluronan, full-length TSG-6 also binds free hyaluronan and all chondroitin sulfate isoforms under physiological conditions. These interactions may contribute to the localization of TSG-6 in cartilage and to its chondroprotective and anti-inflammatory effects in models of arthritis.     

Ion transport through dimethyl sulfoxide (DMSO) induced transient water pores in cell membranes

It is well known that dimethyl sulphoxide (DMSO) increases membrane permeability, which makes it widely used as a vehicle to facilitate drug delivery across biological membranes. However, the mechanism of how DMSO increases membrane permeability has not been well understood. Recently, molecular dynamics simulations have demonstrated that DMSO can induce water pores in biological membranes, but no direct experimental evidence is so far available to prove the simulation result. Using FluxOR Tl? influx assay and intracellular Ca2? imaging technique, we studied the effect of DMSO on Tl? and Ca2? permeation across cell membranes. Upon application of DMSO on CHO-K1 cell line, Tl? influx was transiently increased in a dose-dependent manner. The increase in Tl? permeability induced by DMSO was not changed in the presence of blockers for K? channel and Na?-K? ATPase, suggesting that Tl? permeates through transient water pores induced by DMSO to enter into the cell. In addition, Ca2? permeability was significantly increased upon application of DMSO, indicating that the transient water pores induced by DMSO were non-selective pores. Furthermore, similar results could be obtained from RAW264.7 macrophage cell line. Therefore, this study provided experimental evidence to support the prediction that DMSO can induce transient water pores in cell membranes, which in turn facilitates the transport of active substances across membranes.     

Changes in the cytochrome composition of Rhodopseudomonas sphaeroides grown aerobically, photosynthetically and on dimethyl sulphoxide.

Several strains and mutants of Rhodopseudomonas sphaeroides can be grown anaerobically in the dark in the presence of dimethyl sulphoxide as an electron acceptor. During adaptation to this fermentative mode of growth, two major c-type cytochromes are synthesized, one with Mr 45 000 and the second with Mr 20 000 and a midpoint potential of +120 mV. These cytochromes are barely detectable in membranes prepared from cells grown in aerobic or photosynthetic conditions. An electrophoretic method is presented for the detection of the b-type and c-type cytochromes of pigmented or unpigmented membranes. The method resolves three b-type cytochromes and four c-type cytochromes in membranes from aerobically and photosynthetically grown cells.