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PubMed2000

Structural changes during ATP hydrolysis activity of the ATP synthase from Escherichia coli as revealed by fluorescent probes.

F1F0-ATPase complexes undergo several changes in their tertiary and quaternary structure during their functioning. As a possible way to detect some of these different conformations during their activity, an environment-sensitive fluorescence probe was bound to cysteine residues, introduced by site-directed mutagenesis, in the gamma subunit of the Escherichia coli enzyme. Fluorescence changes and ATP hydrolysis rates were compared under various conditions in F1 and in reconstituted F1F0. The results are discussed in terms of possible modes of operation of the ATP synthases.

Adenosine Diphosphate↗
PubMed1976

[Spectroscopic study of the structural changes of scorpion hemocyanin, induced by pH variations and addition of various salts].

Structural modifications of the scorpion haemocyanin induced by pH variations and salt addition are studied by U.V. absorption, fluorescence, circular dichroism and light scattering. Haemocyanin fluorescence is due to both aromatic amino-acids tyrosine and tryptophan. Deoxygenation or denaturation lead to a fourfold enhancement of its intensity. At acidic pH the active site is modified and the protein is dissociated, but at alkaline pH the haemocyanin aggregates. The addition of different salts (sodium citrate, potassium bromide and iodide...) involves protein dissociation, the amplitude of which depends on the anion. But pH variations and salt addition don't change the haemocyanin secondary structure as shown by circular dichroism. The C.D. spectrum of scorpion haemocyanin exhibits the characteristic bands of Arthropod haemocyanine.

Animals↗
PubMed1993

Three-dimensional structural changes of hepatic sinusoids in cirrhosis providing an increase in vascular resistance of portal hypertension.

A quantitative topological analysis of the three-dimensional sinusoidal structure of five normal human livers and ten cirrhotic livers was performed with the aid of a computer system for reconstruction from serial tissue sections. The mean cycle rank (number of independent cycles) of the sinusoidal network in the examined tissue, 200 x 200 x 80 microns 3 in size, was 181.2 +/- 23.9 in the normal liver and 84.9 +/- 19.1 in the cirrhotic liver. There was a statistically significant difference between the two values (P < 0.001), while there was no significant difference in the sinusoidal volume of the same size tissue between the normal liver and cirrhotic liver. It was found therefore that the sinusoidal network of the cirrhotic liver was more sparsely and coarsely connected in three-dimensional space than that of the normal liver. In addition, there was no significant difference in the mean sinusoidal radius or in the distribution of 1/(radius)4 values between the normal liver and the cirrhotic liver. Resistance changes of the lattice sinusoidal model, where resistance of each sinusoidal branch is proportional only to its length, were then studied. In the lattice model analysis, the resistance between the two endpoints becomes larger as the cycle rank of the network model decreases. This fact suggests that in portal hypertension of cirrhosis the three-dimensional structural change of sinusoids, that is, decrease in the cycle rank, plays a role of increased vascular resistance within regenerative nodules.

Adult↗
PubMed1998

Structure changes in hemoglobin upon deletion of C-terminal residues, monitored by resonance Raman spectroscopy.

Loss of C-terminal residues in hemoglobin raises oxygen affinity and reduces both cooperativity and the Bohr effect. These functional changes are expected from the loss of C-terminal salt bridges, which are seen crystallographically to stabilize the T quaternary structure. Ultraviolet resonance Raman (UVRR) difference spectroscopy confirms that the strength of the T state contacts is diminished when the C-terminal and also the penultimate residues are removed chemically. Deoxy minus CO difference signals arising from the Trpbeta37-Aspalpha94 and Tyralpha42-Aspbeta99 H bonds at the alpha1 beta2 subunit interface are diminished, and at pH 9, the difference spectra reveal a shift to the R quaternary structure. These effects are small for desHisbeta146 Hb and large for desArgalpha141 Hb, consistent with the order of functional changes. In addition, the H bond between the A and E helices is strengthened by removal of Argalpha141 and is further strengthened when the effector molecule IHP (inositol hexaphosphate) is added to deoxy-desArgalpha141 Hb or when its pH is lowered to 5.8. This effect is attributed to the loss of the C-terminal anchor of the alpha chain H helix, which supports the F and A helices. The beta chain is not as sensitive because it has extra F-H interhelix H bonds. Removal of both Hisbeta146 and Tauyrbeta145 produce UVRR changes which are intermediate between desHisbeta146 and desArgalpha141 Hb, although the functional consequences are greater than for desArgalpha141 Hb. Removal of Tyralpha140 as well as Argalpha141 abolishes cooperative binding as well as the Bohr effect, and the UVRR difference signals are also lost, suggesting that quaternary constraints are removed in both the T and the R states. When the approximately 220 cm-1 iron-histidine stretching vibration of the deoxy-proteins is examined, using Raman excitation in resonance with the heme Soret band, the frequency is observed to diminish toward that of deoxyHb A (215 cm-1) as the pH is lowered and IHP is added and to increase toward a completely relaxed value (223 cm-1) as the pH is raised to 9. The relaxation is in the same order as the functional perturbations: desHisbeta146 < desArgalpha141 < desHisbeta146-Tyrbeta145 < desArgalpha141-Tyralpha140. However, even desArgalpha141-Tyralpha140 Hb shows significant reduction in the Fe-His frequency as IHP is added at low pH. The Fe-His frequency is sensitive to both tertiary and quaternary structure changes and is a global indicator of forces at the heme. The order of affinity changes can be understood on the basis of the number of stabilizing H bonds between the F and H helices. Titration curves of the Fe-His frequency against pH are not sigmoidal, consistent with a multiplicity of contributions to the Bohr effect.

Adult↗
PubMed1979

Structural changes in single muscle fibers after stimulation at a low frequency.

Direct stimulation of single muscle fibers from Xenopus laevis at a frequency of 1 Hz results in a decline of the peak isometric twitch tension after about 200 twitches. Fibers were chemically fixed in glutaraldehyde after a varying number of twitches and at several fatigue levels, and the ultrastructural appearance was compared with that of resting fibers treated by identical fixation methods. No gross structural abnormalities were observed but subtle changes occurred. The mitochondria of stimulated fibers contain granules of normal size and number. The inner crista width is constant but the matrix width is increased on stimulation. These changes would not compromise ATP production. The myofibrils are normal except for a slight swelling in the myosin lattice. The transverse system (T system) and sarcoplasmic reticulum are intact. The minor diameter of the transverse tubule (T tubule) is increased slightly in stimulated fibers. The gap between the T-TC membranes stays constant at about 110 A, but tiny connecting pillars are seen to cross this gap more frequently in stimulated fibers (21 +/- 5% triads) than in resting fibers (8 +/- 6%). In stimulated fibers there is a marked increase in the electron dense content of the terminal cisternae (TC). Inasmuch as the observed structural changes correlate with the number of twitches but not with the fatigue level, it is concluded that TC density and T-TC pillar formation are related to the normal mechanisms of excitation-contraction coupling.

Action Potentials↗
PubMed1993

Investigation of secondary and tertiary structural changes of cytochrome c in complexes with anionic lipids using amide hydrogen exchange measurements: an FTIR study.

The structure of cytochrome c bound to anionic lipid membranes composed of dimyristoyl, dipalmitoyl, or dioleoyl phosphatidylglycerols, or of bovine heart cardiolipin, has been investigated by Fourier transform infrared spectroscopy. Only small changes in secondary structure, as registered by the amide I band of cytochrome c, were observed upon binding at temperatures below that of denaturation of the protein, and these were not coupled to the thermotropic phase transitions of the lipid. The denaturation temperature of the protein decreased by approximately 25-30 degrees upon binding, in a progression which correlated with that of the lipid phase transition temperatures, being approximately 7 degrees lower for complexes with dioleoyl than with dipalmitoyl phosphatidylglycerol. Large changes in the amide proton exchange characteristics, as monitored by the spectral shifts in the amide I band of the protein in D2O, were observed on binding cytochrome c to the lipid membranes. For the slowly exchanging population, the amide deuteration rates of the free protein were nearly independent of temperature, whereas those of the bound protein increased by up to two orders of magnitude over the temperature range from 10 to 40 degrees C. In addition, the extent of exchange differed between the bound and unbound protein. A structural transition in the bound protein was detected as a discontinuous step in Arrhenius plots of the deuterium exchange rates which occurred at a temperature in the region of 22 to 29 degrees C, depending on the lipid, far below that of denaturation. The temperature of this transition was determined by the physical state of the lipid, being 7 degrees lower for the lipids in the fluid state than for those in the gel state, and, for complexes with dimyristoyl phosphatidylglycerol, occurred at an intermediate temperature, being controlled by the lipid chain-melting transition at 27-28 degrees C. These results provide evidence for a coupling of the tertiary structure of the membrane-bound protein with the physical state of the membrane lipids.

Animals↗
PubMed1977

[Electron microscopic study of the interaction of shigellae with cell cultures. III. Functional-structural changes in transplanted amniotic cells exposed to extracellular Flexner shigellae].

A quantitative changes of RNA and proteins and structural peculiarities of compensative-regenerative character were discovered in amnion cells subjected to the action of extracellular virulent shigellas by means of successive cytophotometry and electron microscopy. The long contact with the bacteria lead to increased degenerative changes in the cell cytoplasm. The arising changes seem to involve toxicity caused by the action of exometabolites of Shigella flexneri.

Amnion↗
PubMed2003

Alternative prion structural changes revealed by high pressure.

At high temperature, recombinant hamster prion protein (SHaPrP(90-231)) undergoes aggregation and changes from a predominantly alpha-helical to beta-sheet conformation. We then applied high pressure (200 MPa) to the beta-sheet-rich conformation. The aggregation was reversed, and the original tertiary and secondary structures were recovered at ambient pressure, after pressure release. The application of a pressure of 200 MPa thus allowed studying the heat-induced equilibrium refolding in the absence of protein aggregation. Prion protein unfolding as a function of high pressure was also investigated. Simple two-state, reversible unfolding transitions were observed, as monitored by spectral changes in the UV and fluorescence of the hydrophobic probe 8-anilino-1-naphthalene sulfonate. However, these heat- and pressure-induced conformers differed in their unfolding free energy. At pressures over 400 MPa, strong thioflavin-T binding was observed, suggesting a further structural change to a metastable oligomeric structure.

Animals↗
PubMed1998

Vascular and structural changes in rat femora following nailing and intramedullary occlusion.

The purpose of this study was to evaluate biomechanical, structural, and blood flow changes of the femoral canal in rats 12 weeks after intramedullary reaming, nailing, or occlusion. In one group, reaming alone was performed. In a second group, reaming was followed by use of a tight-fit steel nail. In a third group, reaming was followed by use of inert silicone that totally plugged the medullary cavity. A fourth group served as the control. The acute mechanical and vascular effects caused by reaming and nailing were determined in a separate group. Reaming and nail insertion reduced blood flow in femoral bone to about one-third. Reaming reduced bending moment by approximately 40%, whereas bending rigidity was unchanged. After 12 weeks, the cortical bone blood flow was significantly increased in both the nailed and the silicone-plugged bones compared with the reamed and control groups. The bending moment and energy absorption in the silicone group were inferior to those of the other groups. There were no differences in either the external or internal diameter or the medullary and net bone areas. In the silicone group, both the number and the area of large pores (larger than 10 microm) significantly increased in comparison with the other groups; hence, bone porosity was increased. This increment was confined to large pores. It is concluded that medullary occlusion contributes to structural and blood flow changes in bone.

Animals↗
PubMed1977

Salt-induced structural changes in nucleosomes.

Nucleosomes and oligonucleosomes were prepared by digestion of human placental nuclei with staphlococcal nuclease and fractionated by gel filtration chromatography. The effect of increasing salt on the structure of nucleosomes was examined in the presence and absence of 10 mM MgCl2. Nucleosomes and oligonucleosomes are insoluble over a broad range of salt concentration. Nucleosomes are insoluble in larger than or equal to 120 mM (NH4)2SO4 containing 10 mM MgCl2 allowing analyses of changes in nucleosomal DNA by C.D. spectroscopy. Nucleosomes are insoluble in less than or equal to 120 mM (NH4)2SO4 containing 10 mM MgCl2 as demonstrated by turbidity measurements. We conclude that the insolubility of nucleosomes accompanies salt-induced structural changes possibly due to individual particle condensation. As the salt concentration is increased the nucleosomes condense and then relax at higher salt concentrations.

Ammonium Sulfate↗
PubMed1995

Evaluation of biochemical and structural changes in individual porcine corpora lutea during prostaglandin F2 alpha-induced luteolysis with an in vivo implant system.

To date, no in vitro system has been devised to allow the study of both the functional and the structural regression of luteal cells in response to prostaglandin (PG) F2 alpha. This study describes the use of a novel intraluteal PGF2 alpha implant system that results in the death of individual corpora lutea (CL), while surrounding CL on the same ovary remain fully functional. By this technique, it was possible to study both the functional and the structural regression of individual CL in vivo, without the confounding effects resulting from the systemic injection of PGF2 alpha. Biochemical measurements of individual CL included progesterone concentration, protein kinase C activity, and diacylglycerol levels. Structural measurements included luteal weight and the protein:DNA ratio, which was used to estimate cell size. Further, the determination of large luteal cell size was accomplished directly via light microscopy. Nonpregnant gilts were injected with 5 mg of estradiol benzoate every 12 hr from 8:00 a.m. on Day 11 to 8:00 a.m. on Day 13 to prevent uterine PGF2 alpha secretion. At 7:00 a.m. on Day 13, CL on one ovary were selected at random to receive PGF2 alpha-implants (n = 4) or implant material only (n = 4), whereas the remaining CL on that ovary served as unimplanted controls. The other ovary was removed at the point, and the CL on that ovary served as 0-hr controls. Gilts were relaparotomized at 3, 6, 12, and 24 hr after CL implantation, the PGF2 alpha-implanted ovary was removed, and individual CL were evaluated. PGF2 alpha-implanted CL exhibited a decline (P < 0.05) in progesterone concentrations at 12 and 24 hr and a decline (P < 0.05) in weight at 24 hr when compared with control CL (implant-only, unimplanted, and 0-hr control CL). Furthermore, the protein:DNA ratio was reduced (P < 0.10) in the PGF2 alpha-treated CL at 12 and 24 hr. Moreover, this change in the protein:DNA ratio (cell size) was consistent with the reduced diameter (P < 0.05) of the large luteal cell in the PGF2 alpha-treated CL. Protein kinase C activity and diacylglycerol concentrations did not change (P > 0.10) and therefore appear to be unassociated with either functional or structural changes in the PGF2 alpha-treated CL. Contrary to in vitro culture studies, the results of our in vivo study demonstrate no clear role for protein kinase C in the PGF2 alpha-induced luteolytic process.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Structural changes in the kidney induced by coarctation hypertension.

We investigated structural alterations in renal tissue identifying the morphological and histological changes in the non-ischemic kidney (NIK) and their potential significance in aortic coarctation-hypertensive rats (HR). HR's mean arterial pressure (MAP) was higher compared with sham operated rats (SR). An oral 10 mg/kg/day losartan (LOS) dose diminished but not reverted MAP. Hypertrophy was noted in HR NIK's with significant weight increase (p<0.01). The ratio IK/NIK in HR's decreased 22% (p<0.01). LOS proved to cause no ischemic kidney (IK) modification nor did it revert NIK hypertrophy. NIK in HR's presented glomerulosclerosis, mesangial proliferation and arteriolar thickening reverted by LOS. The stereological study of afferent NIK arterioles showed hypertrophy and an increase in the wall/lumen ratio without lumen modification. LOS diminished wall thickness. LOS-induced decrease of NIK alterations might result from arteriosclerosis regression, the media/lumen ratio. glomerulosclerosis and mesangial proliferation dependent on angiotensin 11.

Animals↗
PubMed2000

BSA structural changes during homomolecular exchange between the adsorbed and the dissolved states.

The secondary structure and the thermostability of bovine serum albumin (BSA), before adsorption and after homomolecular displacement from silica and polystyrene particles, are studied by circular dichroism spectroscopy and differential scanning calorimetry. The structural perturbations induced by the hydrophilic silica surface are reversible, i.e. BSA completely regains the native structure and stability after being exchanged. On the other hand, the adsorption on, and subsequent desorption from, polystyrene particles causes irreversible changes in the stability and (secondary) structure of BSA. The exchanged proteins have a higher denaturation temperature and a lower enthalpy of denaturation than native BSA. The alpha-helix content is reduced while the beta-turn fraction is increased in the exchanged molecules. Both effects are more pronounced when the protein is displaced from less crowded sorbent surfaces. The irreversible surface-induced conformational change may be related to some aggregation of BSA molecules after being exposed to a hydrophobic surface.

Animals↗
PubMed1981

Use of fluorescent probes that form intramolecular excimers to monitor structural changes in model and biological membranes.

1,3-dipyrenylpropane (PC3P) and bis(4-biphenylmethyl)ether, two molecules that form intramolecular excimers, were embedded in phospholipid vesicles and biological membranes to monitor dynamic properties of membrane lipids. Excimer formation was evaluated from determinations of excimer to monomer emission intensity ratios (ID/IM). ID/IM values of PC3P and bis(4-biphenylmethyl)ether were reduced when cholesterol was added to egg lecithin vesicles. PC3P was sensitive to the temperature-induced crystalline to liquid-crystalline phase transition in dimyristoyl phosphatidylcholine vesicles. For studies of cellular membranes, membranes, PC3P was used exclusively, because of the fluorescence of tryptophan residues of membrane proteins interferes with the responses bis(4-biphenylmethyl)ether. Microviscosities of membrane interiors were calculated from standard curves of IM/ID plotted against solvent viscosity. Microviscosity values of egg lecithin vesicles and biological membranes, especially those obtained with PC3P, were more than an order of magnitude lower than values obtained by other techniques. We concluded that the intramolecular process leading to the formation of the excimer is influenced differently in isotropic solvents than in anisotropic environments, such as lipid bilayers. Although distinguishable ID/IM ratios can be obtained for different biological membranes (mitochondrial, microsomal, and plasma membranes were studied), this parameter may be phenomenological and not simply related to membrane microviscosity. As such, fluorescent probes that form intramolecular excimers are of value in making qualitative comparisons of different membranes and in studying the relative effects of physical changes and chemical agents on membrane structure. These probes may also be valuable for studying structural anisotropy of biological membranes.

Animals↗
PubMed1985

Salt-dependent structural changes of neurohormones: lithium ions induce conformational rearrangements of ocytocin to a vasopressin-like structure.

The preferred average conformation and structural subdomain interactions of the nonapeptide hormones vasopressin and ocytocin have been analyzed through the determination of their hydrodynamic volume and the thermal coefficient of the frictional resistance to rotation of their tyrosine residue. A spherical gross shape and an ellipsoidal gross shape were assessed respectively for ocytocin and vasopressin by fluorescence polarization analysis. Investigation of the thermal coefficient of viscosity and the critical temperature of both hormones and analogues indicated that strong interactions hold together the two structural subdomains of ocytocin (the flexible six-membered ring and the COOH-terminal tripeptide tail). An opposite situation was found in the case of vasopressin where such interactions could not be detected between the rigid ring and the flexible COOH-terminal tail. Lithium ions were shown to promote ocytocin binding to specific neurophysin sites restricted, under standard conditions, to vasopressin. In the presence of lithium, the gross conformational shape of ocytocin becomes similar to that of vasopressin but in the absence of salt. In addition, the ocytocin ring becomes more rigid in the presence of lithium while decreasing interactions between the ring and the COOH-terminal tail were detected. It is proposed that lithium ions induce specific conformational rearrangements of ocytocin toward a vasopressin-like structure, allowing recognition of this hormonal ligand by a specific vasopressin binding domain of neurophysins.

Amino Acid Sequence↗
PubMed1990

[Study of structural changes in canine maxillary trabecular bone after tooth extraction].

All teeth on the right side of the upper and lower jaws were extracted from canine specimens; and changes in maxillary trabecular-bone structure caused by the resultant reduction in functional pressure were studied by means of image analysis of trabecular-bone density, width, specific length (which indicates bone length to unit area), and trabecular-bone orientations. Results 1. Trabecular-bone density Over the 13-month period, in comparison with the normal side, trabecular-bone density on the experimental side dropped to 69.4% in the incisor region, 82.2% in the premolar region, and from 60.0 to 68.0% in the molar region. The greatest reduction occurred in the molar region. 2. Trabecular-bone width Over the 13-month period, in comparison with the normal side, trabecular-bone width on the experimental side dropped to 86.9% in the incisor region, 86.1% in the premolar region, and from 66.4 to 71.4% in the molar region. The greatest reduction occurred in the molar region. 3. Specific length Over the 13-month period, in comparison with the normal side, specific length on the experimental side dropped to 81.9% in the incisor region, 82.9% in the premolar region, and from 65.6 to 70.5% in the molar region. The greatest reduction occurred in the molar region. 4. Orientation No regular trabecular-bone orientation was observed in the tooth-extraction sockets. In the incisor region, trabecular bone was often distributed at from 100 degrees to 120 degrees in relation to the dental roots. As time passed after extraction, the amount of bone with this orientation gradually decreased. At 13 months, amounts with bone orientation of from 40 degrees to 60 degrees had increased. In the premolar region, a great deal of trabecular bone was oriented at from 140 degrees to 150 degrees in relation to the dental roots. As time passed after extraction, the amount of bone with this orientation gradually decreased. At 13 months, amounts with bone orientation of from 110 degrees to 130 degrees had increased. In the molar buccal region, trabecular bone was often distributed at from 20 degrees to 40 degrees, and 90 degrees in relation to the dental roots. In the molar palatal region, trabecular bone was often distributed at from 120 degrees to 140 degrees in relation to the dental roots. At 13 months, the amount of trabecular bone oriented at about 90 degrees had increased.

Alveolar Bone Loss↗
PubMed1987

Antithrombin conformation and the catalytic role of heparin. I. Does cleavage by thrombin induce structural changes in the heparin-binding region of antithrombin?

Heparin has been shown to exhibit lower affinity for the antithrombin-thrombin complex than for antithrombin alone (Carlstrom, A.-S., Lieden, K., and Bjork, I. (1977) Thromb. Res. 11, 785-797), suggesting that structural alterations in antithrombin may accompany its reaction with thrombin. The hydroxy-nitrobenzyl (HNB) group attached to a unique tryptophan has been used in the present study as an extrinsic probe for localization of conformational changes to the heparin-binding region within antithrombin III using immunochemical and spectral techniques. Site-specific modification of tryptophan-49 in antithrombin with the hydroxynitrobenzyl reagent blocks heparin binding to the protein and provides a chemical label in the heparin-binding region of the protein (Blackburn, M. N., Smith, R. L., Carson, J., and Sibley, C. C. (1984) J. Biol. Chem. 259, 939-941). Antibodies specific for the hydroxynitrobenzyl hapten, which bind to HNB-tryptophan-49 in antithrombin, were used to detect a change in conformation in the region of tryptophan-49 which occurs upon thrombin binding to antithrombin. This thrombin-induced structural change was also apparent from spectral perturbations which were detected with the environmentally sensitive HNB moiety. Thus, the HNB group was used as an immunochemical probe as well as a spectral reporter group to provide insight into an allosteric mechanism of control in the catalytic role of heparin. The thrombin-promoted alteration of the structure in the heparin-binding region is presumably responsible for recycling of heparin, allowing it to catalyze further reactions between antithrombin and thrombin.

Antibodies↗