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PubMed2000

Spectroscopic and electrochemical studies on structural change of plastocyanin and its tyrosine 83 mutants induced by interaction with lysine peptides.

Interactions of wild-type and Tyr83 mutant (Y83F, Y83S, Y83L, and Y83H) plastocyanins (PCs) with lysine peptides as models for the PC interacting site of cytochrome f have been studied by absorption, resonance Raman, and electron paramagnetic resonance (EPR) spectroscopies and electrochemical measurements. The spectral and electrochemical properties of PCs corresponded well with each other; species having a longer wavelength maximum for the S(Cys) pi --> Cu 3d(x)()()2(-)(y)()()2 charge transfer (CT) band observed around 600 nm and a stronger intensity for the 460-nm absorption band exhibited stronger intensities for the positive Met --> Cu 3d(x)()()2(-)(y)()()2 and negative His pi(1) --> Cu 3d(x)()()2(-)(y)()()2 circular dichroism (CD) bands at about 420 and 470 nm, respectively, a lower average nu(Cu)(-)(S) frequency, a smaller |A( parallel)| EPR parameter, and a higher redox potential, properties all related to a weaker Cu-S(Cys) bond and a more tetrahedral planar geometry for the Cu site. Similarly, on oligolysine binding to wild-type and several Tyr83 mutant PCs, a longer absorption maximum for the 600-nm CT band, a stronger intensity for the 460-nm absorption band, stronger 420-nm positive and 470-nm negative CD bands, and a lower average nu(Cu)(-)(S) frequency were observed, suggesting that PC assumes a slight more tetrahedral geometry on binding of oligolysine. Since changes were observed for both wild-type and Tyr83 mutant PCs, the structural change due to binding of oligolysine to PC may not be transmitted through the path of Tyr83-Cys84-copper by a cation-pi interaction which is proposed for electron transfer.

Amino Acid Substitution↗

PubMed2003

Structural changes in the glycosaminoglycan chain of rat skin decorin with growth.

Decorin controls collagen fibrilogenesis in skin, and its molecular weight changes in wound healing and with age. In this report, the quantitative and structural changes of decorin were investigated with growth in rat skin from the fetus to the young adult. A northern blot analysis showed that the highest level of skin decorin mRNA was at post partus 0.5 days; this level was about 3.7 times the level at embryo 16.5 days. The mRNA level in the rat skin decreased by 1/5 from post partus 0.5 days until 90 days of age. Western blotting showed that the amount of decorin increased with age in protein level. The molecule size of decorin at embryo 18.5 days was about 110 kDa, and that at post partus 90 days was about 70 kDa. There were no changes in molecular size of its core protein, so the reduction in the size of decorin was dependent on the size of the glycosaminoglycan (GAG) as shown by western blot analyses. Electron micrography of the rat skin with cupromeronic blue staining showed that the length of GAG at embryo 18.5 days was about 78.58 +/- 13.94 nm, and that at post partus 90 days was about 54.05 +/- 4.79 nm. The reduction in length of decorin GAG with age shrunk the distance between the collagen fibrils. We suggested that decorin changes the GAG length in order to control skin reconstruction in response to inflammation and injury.

Aging↗

PubMed2003

Structural changes, P-P bond energies, and homolytic dissociation enthalpies of substituted diphosphines from quantum mechanical calculations.

The molecular structures of the diphosphines P(2)[CH(SiH(3))(2)](4), P(2)[C(SiH(3))(3)](4), P(2)[SiH(CH(3))(2)](4), and P(2)[Si(CH(3))(3)](4) and the corresponding radicals P[CH(SiH(3))(2)](2), P[C(SiH(3))(3)](2), P[SiH(CH(3))(2)](2), and P[Si(CH(3))(3)](2) were predicted by theoretical quantum chemical calculations at the HF/3-21G*, B3LYP/3-21G*, and MP2/6-31+G* levels. The conformational analyses of all structures found the gauche conformers of the diphosphines with C(2) symmetry to be the most stable. The most stable conformers of the phosphido radicals were also found to possess C(2) symmetry. The structural changes upon dissociation allow the release of some of the energy stored in the substituents and therefore contribute to the decrease of the P-P bond dissociation energy. The P-P bond dissociation enthalpies at 298 K in the compounds studied were calculated to vary from -11.4 kJ mol(-1) (P(2)[C(SiH(3))(3)](4)) to 179.0 kJ mol(-1) (P(2)[SiH(CH(3))(2)](4)) at the B3LYP/3-21G* level. The MP2/6-31+G* calculations predict them to be in the range of 52.8-207.9 kJ mol(-1). All the values are corrected for basis set superposition error. The P-P bond energy defined by applying a mechanical analogy of the flexible substituents connected by a spring shows less variation, between 191.3 and 222.6 kJ mol(-1) at the B3LYP/3-21G level and between 225.6 and 290.4 kJ mol(-1) at the MP2/6-31+G* level. Its average value can be used to estimate bond dissociation energies from the energetics of structural relaxation.

Journal Article↗

PubMed2003

Laves-phase structural changes in the system CaAl2-xMgx.

Compounds CaAl(2)(-)(x)Mg(x) (0 < or = x < or = 2) were synthesized and structurally characterized by X-ray diffraction experiments. With increasing Mg content x the sequence of Laves phase structures MgCu(2) --> MgNi(2) --> MgZn(2) is revealed. The homogeneity ranges of the underlying phases were determined to be 0 < or = x < 0.24(1) (MgCu(2) type), 0.66(2) < x < 1.07(3) (MgNi(2) type), and 1.51(5) < x < or = 2.0 (MgZn(2) type). Mg/Al site occupancies in CaAl(1.34)Mg(0.66) and in CaAl(0.44)Mg(1.56) were refined from neutron powder diffraction experiments and exposed a pronounced segregation of Al and Mg in MgNi(2)-type CaAl(1.34)Mg(0.66) where Al atoms preferentially occupy the positions corresponding to trigonal bipyramids. In MgZn(2)-type CaAl(0.44)Mg(1.56), however, the Mg/Al distribution was found to be nearly uniform. Structural stability in the quasi-binary system CaAl(2)(-)(x)Mg(x) was investigated by first-principles calculations in which random occupational disorder of Mg and Al was modeled with the virtual crystal approximation. The theoretical calculations reproduced the experimental compositional stability ranges of the three different Laves phase structures very well. Structural changes in the quasi-binary system CaAl(2)(-)(x)Mg(x) are induced by the electron concentration, which decreases with increasing x. The stability of the different Laves phase structures as a function of electron concentration was analyzed by the method of moments.

Journal Article↗

PubMed2003

Light-induced structural changes in the LOV2 domain of Adiantum phytochrome3 studied by low-temperature FTIR and UV-visible spectroscopy.

Phototropin (Phot) is a blue-light receptor in plants. The molecule has two FMN (flavin mononucleotide) binding domains named LOV (light-, oxygen-, and voltage-sensing), which is a subset of the PAS (Per-Arnt-Sim) superfamily. Illumination of the phot-LOV domains in the dark state (D447) produces a covalent C(4a) flavin-cysteinyl adduct (S390) via a triplet excited state (L660), which reverts to D447 in the dark. In this work, we studied the light-induced structural changes in the LOV2 domain of Adiantum phytochrome3 (phy3), which is a fusion protein of phot containing the phytochrome chromophoric domain, by low-temperature UV-visible and FTIR spectroscopy. UV-visible spectroscopy detected only one intermediate state, S390, in the temperature range from 77 to 295 K, indicating that the adduct is produced even at temperatures as low as 77 K, although a portion of D447 cannot be converted to S390 at low temperatures possibly because of motional freezing. In the whole temperature range, FTIR spectra in the S-H stretching frequency region showed that Cys966 of phy3-LOV2 is protonated in D447 and unprotonated on illumination, supporting adduct formation. The pK(a) of the S-H group in D447 is estimated to be >10. FTIR spectra also showed the light-induced appearance of a positive peak around 3621 cm(-1) in the whole temperature range, indicating that adduct formation accompanies rearrangement of a hydrogen bond of a water molecule(s), which can be either water25, water45, or both, near the chromophore. In contrast to the weak temperature dependence of the spectral changes in the UV-visible absorption and the FTIR of both S-H and O-H stretching bands, light-induced changes in the amide I vibration that probes protein backbone structure vary significantly with the increase in temperature. The spectral changes suggest that light excitation of FMN loosens the local structure around it, particularly in turns, in the early stages and that another change subsequently takes place to tighten it, mainly in beta-structure, but some occur in the alpha-helical structure of the protein moiety as well. Interestingly, these changes proceed without altering the shape of UV-visible spectra, suggesting the presence of multiple conformation states in S390.

Adiantum↗

PubMed2006

Early structural changes of aortic wall in sinoaortic-denervated rats.

1. The present work was designed to observe the early structural changes in the aortic wall in Sprague-Dawley rats 1, 2 and 4 weeks after sinoaortic denervation (SAD). 2. Rats were examined 1, 2 and 4 weeks after SAD. Blood pressure (BP) was recorded in the conscious state. The thoracic aortas were taken for investigations, including: light microscopy, electron microscopy, immunohistochemistry and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labelling (TUNEL). 3. Blood pressure variability (BPV) was significantly increased in the SAD groups 1, 2 and 4 after the operation when compared with the sham-operated ones. 4. Two weeks after SAD the percentage proportion of smooth muscle cell density (SMC%) was obviously increased. 5. Four weeks after SAD: the SMC%, percentage proportion of collagen density (CD%) and aortic wall thickness (WT) were obviously increased with vascular smooth muscle cells blebbing concomitantly. Endothelial cells showed degenerative changes and swelling with blebbing of the cell membrane and increased condensation of peripheral nuclear chromatin and cytoplasmic vacuolization. It was also found that the number of apoptotic endothelial cells was increased and expression of eNOS was reduced. 6. This is the first study that shows the time-course of aortic wall and endothelial cell changes induced by SAD. Increased BPV might be the priming factor in the development of organ damage induced by SAD.

Animals↗

PubMed1977

Structural changes in the outer retinal layers following blunt mechanical non-perforating trauma to the globe: an experimental study.

Structural changes in the external retinal layers of pigs' eyes that had previously been subjected to blunt non-perforating mechanical injuries have been described. Within minutes of trauma fragmentation of the photoreceptor outer segments and damage to the retinal pigment epithelium was recorded in areas of retina adjacent to the missile impact site on the sclera. One week after injury the disrupted photoreceptor outer segments disappeared, and the inner segments came to lie adjacent to the retinal pigment epithelium. Evidence of regeneration of photoreceptor outer segments was noted 2 weeks later.

Animals↗

PubMed1983

[The structural changes of the kidney in Lymnaea truncatula Müller infected by Fasciola hepatica L].

The kidney of Lymnaea truncatula showed structural changes when infected by Fasciola hepatica. These changes first occurred at day 21 postexposure at 20 degrees C and concerned a destruction of renal epithelial cells followed by an epithelial hyperplasia. These hyperplasied epithelial cells again showed a destruction at days 49 and 70 post-exposure. The significance of these results is discussed.

Animals↗

PubMedDate not supplied

[A study of protein structure changes during hydration by diffuse X-ray scattering. I. The intensity and the shape of "10-angstrom" maximum].

The angle dependencies of diffuse x-ray scattering intensities were studied in a wide range of angles from 3 to 80 degrees for water-soluble and membrane proteins with a different structural organization: alpha-helical protein myoglobin, alpha-helical protein serum albumen, alpha + beta protein lysozyme, and transmembrane proteins of photosynthetic reaction centers (RC) from purple bacteria Rhodobacter sphaeroides, and Blastochlorii (Rhodopseudomonas) viridis containing cytocrome c, situated out side the membrane, and for H and L+M subunits of membrane protein of reaction center from Rb. sphaeroides for various hydration degrees. The hydration/dehydration process was studied for water-soluble proteins (within hydration range from h = 0.05 to h = 1). The hydration/dehydration process appears to be reversible. All water-soluble proteins show a 10 angstroms peak, and proteins of reaction center do not show this peak. A quantitative comparable study of the behaviour for of the 10 angstroms peak different proteins the degree of lysozyme hydration increases from h = 0.05 to h = 0.45, the protein structure slightly changes (most probably the motifoffolding), the structure of myoglobin in solution is slightly different from the structure in crystal. By taking into account the changes in the shape and intensity of the 10 angstroms peak only, it is impossible to make the conclusion about structural changes in other proteins studied. A correlation between the structural changes observed and dynamic and functional properties of proteins is discussed.

Animals↗

PubMed1993

[A spin-probe study of the structural change in human blood lipoproteins under the action of sodium hypochlorite].

The spin-probe technique was used to study structural changes in the surface proteolipid layer of human blood low-density lipoproteins (LDL) peroxidized to different degree by sodium hypochlorite (NaOCl). The paramagnetic analogs of stearic acid were employed as spin labels that contained nitroxide groups localized at different distances from the LDL surface. In addition, a positively charged spin label was used which was distributed at the lipid-water interface, in the area of polar phospholipid groups. NaOCl was shown to induce the lipid peroxidation of LDL. It diminished the mobility of polar "heads" as well as of acyl phospholipid chains up to 1.7 nm from the LDL particle surface and increased the polarity of lipid phase in this region. In the deeper layers (2.0-2.2 nm) the structural alterations in LDL were registered only at NaOCl concentration more than 1 mM.

Electron Spin Resonance Spectroscopy↗

PubMed1988

Sequential structural changes in the fat body of the tobacco hornworm, Manduca sexta, during the fifth larval stadium.

Light and electron microscopy revealed a series of structural changes that occur in the fat body of the tobacco hornworm, Manduca sexta, during the fifth, i.e. the final, larval stadium. At each developmental stage studied, the cells of the fat body were homogeneous in structure. We found no evidence suggesting the presence of more than one type of fat body cell. Our structural data are consistent with published observations on biochemical activities of M. sexta fat body at particular developmental stages. Specific points of agreement include: (a) acquisition of Golgi complex (GC) and rough endoplasmic reticulum (RER) concomitant with the time of major protein production; (b) loss of many cellular organelles (such as GC and RER) as protein production drastically decreases; (c) accumulation of protein granules and urate granules after the onset of wandering (i.e. during the pre-pupal period); (d) accumulation of lipid and glycogen throughout the feeding period. In addition we found that (a) the plasma membrane reticular system (PMRS) developed during the period when protein secretion was great; (b) the PMRS was lost abruptly at the onset of wandering; and (c) the nucleus changed in shape from being roughly spherical to elliptoid in the pre-pupal stage. We found that the structure of M. sexta fat body is similar to that published for other Lepidoptera. However, it differs from that of Heliothis zea in that regional differences are not obviously apparent.

Animals↗

PubMed1999

Structural changes in the actin-myosin cross-bridges associated with force generation induced by temperature jump in permeabilized frog muscle fibers.

Structural changes induced by Joule temperature jumps (T-jumps) in frog muscle fibers were monitored using time-resolved x-ray diffraction. Experiments made use of single, permeabilized fibers that were fully activated after slight cross-linking with 1-ethyl-3-[3-dimethylamino)propyl]carbodiimide to preserve their structural order. After T-jumps from 5-6 to approximately 17 degrees C and then on to approximately 30 degrees C, tension increased by a factor of 1.51 and 1.84, respectively, whereas fiber stiffness did not change with temperature. The tension rise was accompanied by a decrease in the intensity of the (1, 0) equatorial x-ray reflection by 15 and 26% (at approximately 17 and approximately 30 degrees C) and by an increase in the intensity of the M3 myosin reflection by 20% and 41%, respectively. The intensity of the (1,1) equatorial reflection increased slightly. The peak of the intensity on the 6th actin layer line shifted toward the meridian with temperature. The intensity of the 1st actin layer line increased from 12% (of its rigor value) at 5-6 degrees C to 36% at approximately 30 degrees C, so that the fraction of the cross-bridges labeling the actin helix estimated from this intensity increased proportionally to tension from approximately 35% at 5-6 degrees C to approximately 60% at approximately 30 degrees C. This suggests that force is generated during a transition of nonstereo-specifically attached myosin cross-bridges to a stereo-specific binding state.

Actomyosin↗

PubMed1995

Structural changes in actin-tropomyosin during muscle regulation: computer modelling of low-angle X-ray diffraction data.

The crystal structure of G-actin monomer has been used together with tropomyosin in a filament model to explain the low-angle X-ray diffraction data from relaxed and activated actin filaments. The four-subdomain actin monomer can be approximated quite well by a four-sphere unit. Orienting this unit and tropomyosin into a filament by searching for the best fit between the computed Fourier transform and the observed vertebrate skeletal muscle low-angle actin layer-lines from muscles at non-overlap sarcomere lengths produced models for the structural changes within the thin filaments (actin plus tropomyosin) between the resting state and the active states, which occur as a result of calcium-activation and independent of myosin interaction with actin. The models are very sensitive to changes in the positions of the centres of mass of the subdomains, but not to the exact shape of the objects used to represent them (e.g. spheres, ellipsoids etc.), as long as the volume is fixed, at the resolution here considered. It is concluded that, even with a four-subdomain structure for the actin molecules, the observed low-angle X-ray diffraction patterns cannot be explained without a substantial azimuthal swing of the tropomyosin strands when resting filaments are calcium-activated. The direction of this swing upon calcium-activation is away from a position close to the proposed major binding site of the myosin head on actin; a result consistent with the original "steric blocking model" of thin filament-based regulation in which the tropomyosin position on actin is crucial for regulation of the myosin crossbridge cycle on actin. Tropomyosin sterically hindering myosin attachment in the "off" state remains a possibility. However, even in the "on" state, the tropomyosin position is close enough to the myosin-binding site to have an effect, where it could regulate the transition of the head from a weak to a strong state. In addition to this tropomyosin movement there are small, but plausible, actin subdomain movements. A tropomyosin shift on its own will not explain the data. Allowance for possible movement of actin subdomain 2 along with the tropomyosin shift still does not explain the data. An additional small movement of subdomain 1; the main myosin-binding subdomain, is postulated.

Actin Cytoskeleton↗

PubMed1980

Structural changes in the perfused canine kidney exposed to the direct action of endotoxin.

We attempted to clarify whether structural damage or hemodynamic alterations is the primary cause of renal failure in the initial phases of endotoxic shock. Endotoxin (0.5 mg/kg) was infused directly into the renal artery and normal renal hemodynamics were maintained by cross-perfusion and controlled pressure. Direct exposure of renal parenchyma to endotoxin action was followed by changes in structure at the cellular and subcellular levels. The damage was unequally distributed and involved mainly the mitochondria and lysosomes of the distal and proximal convoluted tubules. No significant structural changes could be detected in the glomeruli or in the vascular compartment. There was no direct relationship between the degree of mitochondrial and lysosomal damage and the changes in enzymatic activity. The enzymatic systems associated with active Na transport and glycogen breakdown showed only slight alterations, while those related to energy production, hydrogen transfer and the respiratory activity of the cell were severely affected. These results indicate that structural damage in the nephron may contribute to the renal failure in the initial phase of endotoxemia.

Acid Phosphatase↗

PubMed1976

Structural changes of erythrocyte membranes in muscllar dystrophy.

Erythrocytes from dystrophic hamsters and patients with Duchenne muscular dystrophy were examined for structural changes using light microscopical methods. The effects of specimen preparation were also investigated. The proportions present of echinocytes were significantly greater in dystrophic hamsters and humans when compared with their respective controls. In the dystrophic hamsters, the progression of the myopathy caused a significant increase in erythrocyte membrane deformations. With dystrophic patients, age-related changes were seen, but these were not statistically significant. These findings were discussed with relation to specimen preparation and the use of haematological techniques in the detection of carriers of muscular dystrophy.

Age Factors↗

PubMed1996

Measurement of protein structure change in active muscle by hydrogen-tritium exchange.

A hydrogen-tritium exchange method was developed to study protein structure changes at the molecular level in active muscle. Skinned rabbit psoas fibers mounted on a specially designed holder were selectively tritium labeled at peptide group NH sites that change from a highly protected form in rigor to an easily exchangeable, essentially random coil condition when muscle is activated. The number of sites found to show this behavior varies linearly with thick filament-thin filament overlap, and would correspond to 83 amino acids per myosin molecule in the muscle, although the experiments do not yet place these sites in any given protein. Half of the sensitive sites respond to relaxing conditions as well to activation.

Adenosine Triphosphate↗

PubMed2006

Structural changes in self-assembled monolayers initiated by ultraviolet light.

Self-assembled monolayers of 2-anthracenethiol and 2-naphthalenethiol on gold (111) were irradiated with low-power UV light. Scanning tunneling microscope images recorded in situ show unusual structural changes. In the case of 2-anthracenethiol, structures measuring 4-7 nm wide and 30-40 nm in length are formed. Images taken 10 min after irradiation ceased to show further surface reorganization. With 2-naphthalenethiol SAMs, smaller structures form upon irradiation, which subsequently revert to resemble the original structure after time.

Journal Article↗

PubMed1990

Fine structural changes in the rat arcuate nucleus by forced running stress.

The forced running stress in male rats induced some fine structural changes in the arcuate nucleus. By inducing stress for 2 days, the number of multilamellar astrocytic wrappings and endoplasmic reticular (ER) whorls increased significantly. After a stress of 12 days, half of the rats remained inactive for several weeks, and the other half regained their normal activity. In the inactive group, the ER whorls were partially degenerated at 2 weeks after the stress. These degenerative changes remained for 14 weeks after the stress with the increased lysosomes and the disorganization of r-ER. These findings may suggest that long-term stress induces degenerative changes in the arcuate nucleus neurons and that some of these changes persist with some aging-like morphological changes.

Animals↗