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At least 955 records · Page 53Linked to original sources
PubMed1990

Special considerations in the purification of the GM3 ganglioside forming enzyme, CMP-sialic acid:lactosylceramide alpha 2-3 sialyltransferase (SAT-1): solubilization of SAT-1 with lauryldimethylamine oxide.

Lauryldimethylamine oxide (LDAO) was employed in the purification of the GM3 ganglioside forming enzyme, CMP-sialic acid:lactosylceramide alpha 2-3 sialyltransferase (SAT-1) (4). This detergent has advantages over the typically employed Triton detergents in the solubilization and stabilization of this sialyltransferase. Crude protein fractions solubilized from rat liver Golgi by several such detergents are very similar in composition as determined by two-dimensional gel electrophoresis. However, LDAO appears to activate and stabilize SAT-1 activity. It is possible that SAT-1 activation involves the structurally similar hydrophobic moieties and quaternary amino groups of LDAO and phosphatidylcholine.

Animals↗
PubMed2004

In vitro self-assembly of the light harvesting pigment-protein LH2 revealed by ultrafast spectroscopy and electron microscopy.

Controlled ensemble formation of protein-surfactant systems provides a fundamental concept for the realization of nanoscale devices with self-organizing capability. In this context, spectroscopic monitoring of pigment-containing proteins yields detailed structural information. Here we have studied the association behavior of the bacterial light-harvesting protein LH2 from Rhodobacter spheroides in an n,n-dimethyldodecylamine-n-oxide/water environment. Time-resolved studies of the excitation annihilation yielded information about aggregate sizes and packing of the protein complexes therein. The results are compared to transmission electron microscopy images of instantaneously frozen samples. Our data indicate the manifestation of different phases, which are discussed with respect to the thermodynamic equilibrium in ternary protein-surfactant-water systems. Accordingly, by varying the concentration the formation of different types of aggregates can be controlled. Conditions for the appearance of isolated LH2 complexes are defined.

Bacterial Proteins↗
PubMed1995

Phase equilibria and molecular packing in the N,N-dimethyldodecylamine oxide/gramicidin D/water system studied by 2H nuclear magnetic resonance spectroscopy.

A partial phase diagram of the system N,N-dimethyldodecylamine oxide (DDAO)/water/gramicidin D was determined by 2H-NMR. Both 2H2O and perdeuterated DDAO (DDAO-d31) were studied by solid state NMR techniques. Addition of gramicidin D to the micellar (L1), normal hexagonal (HI) and cubic (I) phases of DDAO induces phase separations, giving two-phase regions, which all contain a lamellar (L alpha) phase. The L alpha phase containing gramicidin is characterized by larger order parameters for DDAO-d31 compared with the corresponding order parameters in the L alpha and HI phases of DDAO-d31/H2O. The L alpha phase may stay in equilibrium with any other phase in the phase diagram. The DDAO exchange between the coexisting phases is slow on the NMR timescale, which is why the recorded NMR spectrum consists of superimposed spectra from the different phases occurring in the sample. Gramicidin D can be solubilized in appreciable quantities only in the lamellar phase of DDAO-d31. Increasing amounts of gramicidin in the liquid crystalline phases result in a continuous increase in the molecular ordering up to about 5 mol% gramicidin, where a plateau is reached. This is consistent with a recent theoretical model describing the influence on the ordering of lipids by a membrane protein with larger hydrophobic thickness than the lipid bilayer. The solvent used for dissolving gramicidin at the incorporation of the peptide in the lipid aggregates has no effect on the 2H-NMR lineshapes of DDAO-d31. It is concluded that gramicidin is solubilized in the L alpha phase and that it always adopts the channel conformation independent of a particular solvent. The channel conformation is also supported by CD studies. In some of the samples, macroscopic orientation of the lipid aggregates is observed. It is concluded that DDAO-d31 in the binary system favors an orientation with the long axis of the hydrocarbon chain perpendicular to the magnetic field, whereas when gramicidin D is present the hydrocarbon chain orients parallel to the magnetic field. This is explained by the fact that gramicidin aligns with its helical axis parallel to the magnetic field, thereby forcing also the DDAO-d31 molecules to obtain such an orientation.

Chemical Phenomena↗
PubMed1997

The interaction of quinone and detergent with reaction centers of purple bacteria. I. Slow quinone exchange between reaction center micelles and pure detergent micelles.

The kinetics of light-induced electron transfer in reaction centers (RCs) from the purple photosynthetic bacterium Rhodobacter sphaeroides were studied in the presence of the detergent lauryldimethylamine-N-oxide (LDAO). After the light-induced electron transfer from the primary donor (P) to the acceptor quinone complex, the dark re-reduction of P+ reflects recombination from the reduced acceptor quinones, QA- or QB-. The secondary quinone, QB, which is loosely bound to the RC, determines the rate of this process. Electron transfer to QB slows down the return of the electron to P+, giving rise to a slow phase of the recovery kinetics with time tau P approximately 1 s, whereas charge recombination in RCs lacking QB generates a fast phase with time tau AP approximately 0.1 s. The amount of quinone bound to RC micelles can be reduced by increasing the detergent concentration. The characteristic time of the slow component of P+ dark relaxation, observed at low quinone content per RC micelle (at high detergent concentration), is about 1.2-1.5 s, in sharp contrast to expectations from previous models, according to which the time of the slow component should approach the time of the fast component (about 0.1 s) when the quinone concentration approaches zero. To account for this large discrepancy, a new quantitative approach has been developed to analyze the kinetics of electron transfer in isolated RCs with the following key features: 1) The exchange of quinone between different micelles (RC and detergent micelles) occurs more slowly than electron transfer from QB- to P+; 2) The exchange of quinone between the detergent "phase" and the QB binding site within the same RC micelle is much faster than electron transfer between QA- and P+; 3) The time of the slow component of P+ dark relaxation is determined by (n) > or = 1, the average number of quinones in RC micelles, calculated only for those RC micelles that have at least one quinone per RC (in excess of QA). An analytical function is derived that relates the time of the slow component of P+ relaxation, tau P, and the relative amplitude of the slow phase. This provides a useful means of determining the true equilibrium constant of electron transfer between QA and QB (LAB), and the association equilibrium constant of quinone binding at the QB site (KQ+). We found that LAB = 22 +/- 3 and KQ = 0.6 +/- 0.2 at pH 7.5. The analysis shows that saturation of the QB binding site in detergent-solubilized RCs is difficult to achieve with hydrophobic quinones. This has important implications for the interpretation of apparent dependencies of QB function on environmental parameters (e.g. pH) and on mutational alterations. The model accounts for the effects of detergent and quinone concentration on electron transfer in the acceptor quinone complex, and the conclusions are of general significance for the study of quinone-binding membrane proteins in detergent solutions.

Benzoquinones↗
PubMed1998

13C solid-state NMR of gramicidin A in a lipid membrane.

The natural-abundance 13C NMR spectrum of gramicidin A in a lipid membrane was acquired under magic-angle spinning conditions. With fast sample spinning (15 kHz) at approximately 65 degrees C the peaks from several of the aliphatic, beta-, alpha-, aromatic, and carbonyl carbons in the peptide could be resolved. The resolution in the 13C spectrum was superior that observed with 1H NMR under similar conditions. The 13C linewidths were in the range 30-100 Hz, except for the alpha- and beta-carbons, the widths of which were approximately 350 Hz. The beta-sheet-like local structure of gramicidin A was observed as an upfield shift of the gramicidin alpha and carbonyl resonances. Under slow sample spinning (500 Hz), the intensity of the spinning sidebands from 13C in the backbone carbonyls was used to determine the residual chemical shift tensor. As expected, the elements of the residual chemical shift tensor were consistent with the single-stranded, right-handed beta6.3 helix structure proposed for gramicidin A in lipid membranes.

Carbon Isotopes↗
PubMed1998

Influence of feeding on metabolite excretion evidenced by urine 1H NMR spectral profiles: a comparison between subjects living in Rome and subjects living at arctic latitudes (Svaldbard).

Urines from 25 normal subjects living in Rome and 25 normal subjects living in Ny-Alesund (Svaldbard) were analysed by 1HNMR spectroscopy. The observed differences in the concentration of the major metabolites were correlated to the composition of the diet. It was found that a diet rich of carbohydrates, such as the Italian diet, is responsible for an increased excretion of citrate, lactate, alanine, and glycine. Thus, a correct diagnostical interpretation of urinary metabolites needs to consider feeding habits.

Adult↗
PubMed2002

Self-assembly of ATP synthase subunit c rings.

Subunit c of the H(+) transporting ATP synthase is an essential part of its membrane domain that participates in transmembrane proton conduction. The annular architecture of the subunit c from different species has been previously reported. However, little is known about the type of interactions that affect the formation of c-rings in the ATPase complex. Here we report that subunit c over-expressed in Escherichia coli and purified in non-ionic detergent solutions self-assembles into annular structures in the absence of other subunits of the complex. The results suggest that the ability of subunit c to form rings is determined by its primary structure.

Bacterial Proton-Translocating ATPases↗
PubMed1976

Determination of urinary monohydric and dihydric phenols by gas chromatography of the acetate and TMS derivatives. 4-Dimethylaminopyridine as a catalyst for acetylation reactions.

A procedure is described for the quantitative extraction of phenols from human urine. The compounds were chromatographed as the trimethylsilyl derivatives on wall-coated glass capillary columns. A more specific method of extraction involving the formation of acetate derivatives is also described. The acetates were prepared by treating dilute solutions of phenols at room temperature with acetic anhydride in the presence of 4-dimethylaminopyridine, which is a far more powerful catalyst than pyridine. Under these conditions N-acylamino acids are converted to azlactones.

4-Aminopyridine↗
PubMed1975

N-dimethylaminomethylene derivatives for the gas-liquid chromatography of primary sulfonamides.

Dimethylformamide dialkylacetals have been found to react readily with primary sulfonamides to form N-dimethylaminomethylene derivatives. These compounds possess excellent gas-liquid chromatographic properties and can be conveniently prepared at the submicrogram level. Their retention times are much greater than those of other sulfonamide derivatives (e.g., N,N-dimethyl) but their ease of preparation and lack of absorptive properties make them attractive for gas-liquid chromatographic studies. The practical applicability of this derivatization approach to biological studies is illustrated by the gas-liquid chromatographic determination of 3-bromo-5-cyanobenzenesulfonamide in ovine blood using 3,5-dibromobenzenesulfonamide as the internal standard. The method has a detection limit of 25 ppb with electron capture detection.

Animals↗
PubMed1975

Quantitative determination of indolic compounds in the rat brain using p-dimethylaminocinnamaldehyde as reagent.

A method is proposed for determining the metabolites of radioactive 5-hydroxytryptophan and of endogenous tryptophan in the rat brain. The compounds are separated by thin-layer chromatography and made visible with p-dimethylaminocinnamaldehyde (DACA) reagent. The conditions studied are those which allow the use of DACA reagent for the quantitative determination of tryptophan metabolites in brain tissue. Amount of 5 ng of serotonin and 20 ng of tryptophan can be determined by densitometry.

5-Hydroxytryptophan↗
PubMed2003

AFM characterization of tilt and intrinsic flexibility of Rhodobacter sphaeroides light harvesting complex 2 (LH2).

Atomic force microscopy (AFM) has developed into a powerful tool to investigate membrane protein surfaces in a close-to-native environment. Here we report on the surface topography of Rhodobacter sphaeroides light harvesting complex 2 (LH2) reconstituted into two-dimensional crystals. These photosynthetic trans-membrane proteins formed cylindrical oligomeric complexes, which inserted tilted into the lipid membrane. This peculiar packing of an integral membrane protein allowed us to determine oligomerization and tilt of the LH2 complexes, but also protrusion height and intrinsic flexibility of their individual subunits. Furthermore the surface contouring reliability and limits of the atomic force microscopy could be studied. The two-dimensional crystals examined had sizes of up to 5 microm and, as revealed by a 10 A cryo electron microscopy projection map, p22(1)2(1) crystal symmetry. The unit cell had dimensions of a = b = 150 A and gamma = 90 degrees, and housed four nonameric complexes, two pointing up and two pointing down. AFM topographs of these 2D crystals had a lateral resolution of 10 A. Further, the high vertical resolution of approximately 1 A, allowed the protrusion height of the cylindrical LH2 complexes over the membrane to be determined. This was maximally 13.1 A on one side and 3.8 A on the other. Interestingly, the protrusion height varied across the LH2 complexes, showing the complexes to be inserted with a 6.2 degree tilt with respect to the membrane plane. A detailed analysis of the individual subunits showed the intrinsic flexibility of the membrane protruding peptide stretches to be equal and independent of their protrusion height. Furthermore, our analysis of membrane proteins within this peculiar packing confirmed the high vertical resolution of the atomic force microscopy on biological samples, and led us to conclude that the image acquisition function was equally accurate for contouring protrusions with heights up to approximately 15 A.

Amino Acid Sequence↗
PubMed2003

Gadolinium chloride reverses dimethylnitrosamine (DMN)-induced rat liver fibrosis with increased matrix metalloproteinases (MMPs) of Kupffer cells.

The aim of this study was to investigate whether matrix metalloproteinases (MMP-13, 9) of Kupffer cells induced by gadolinium chloride (GdCl(3)) treatment can reverse dimethylnitrosamine (DMN)-induced liver fibrosis (in vivo) and the effect of GdCl(3) on MAP kinase activity (in vitro). Male Wistar rats 6 weeks of age received DMN (10 mg/kg) three successive days a week for 4 weeks. Then two groups of rats (n = 6 each) were treated twice weekly with either GdCl(3) (7 mg/kg) or saline solution intravenously for the next 4 weeks. Animals were sacrificed to estimate the degree of liver fibrosis. Isolated Kuppfer cells were treated with GdCl(3) and the expressions of MMPs, MAP kinase activity (ERK, SAPK/JNK, P38) as well as apoptosis were also examined. Rats that received DMN for 4 weeks followed by GdCl(3) injection for 4 weeks showed an reduced liver hydroxyproline content compared to rats treated with DEN followed by saline (277 +/- 22 VS 348 +/- 34 microg/g, n = 6 each, P < 0.01). There were significantly increased MMP-13 mRNA levels in GdCl(3)-treated rats. However, no significant change was observed in procollagen type I mRNA levels. Isolated Kuppfer cells treated with GdCl(3) showed increased MAP kinase activity, especially P38 pathway as well as MMP-13, 9 mRNA and type I collagen-degrading activity leading to apoptosis. SB203580, inhibitor of P38 pathway diminished these activation and prevented apoptosis. These results suggest that Kuppfer cells can reverse liver fibrosis via the expression of MMPs mainly through P38 pathway.

Animals↗