PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Structural changes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1995

Massive osteoarticular knee allografts: structural changes evaluated with CT.

PURPOSE: To analyze the structural changes seen at computed tomography (CT), particularly the findings that precede insufficiency (fatigue) fractures in massive osteoarticular knee allografts. MATERIALS AND METHODS: The subchondral and cancellous bone of 12 allografts were retrospectively evaluated with repeat transaxial CT (mean follow-up, 53 months). RESULTS: Early cortical graft resorption was followed by slow thickening after 6 months. Formation of resorptive cysts increased the cortical irregularity, which leveled off after 2 years. Late remodeling was evident as a subcortical sclerotic rim, "neocortex." Initially, the cancellous graft bone showed higher attenuation than the host bone; this difference subsided gradually during the first 3 years. Four insufficiency fractures were detected after the 1st postoperative year. Poor remodeling preceded these fractures. CONCLUSION: CT effectively depicted the structural changes during allograft incorporation and was superior to plain radiography for the detection of insufficiency fractures. The use of CT for follow-up of massive osteoarticular knee allografts provides additional information concerning the readiness of the graft for weight bearing.

Adolescent↗
PubMed1990

Target-dependent structural changes accompanying long-term synaptic facilitation in Aplysia neurons.

The mechanisms underlying structural changes that accompany learning and memory have been difficult to investigate in the intact nervous system. In order to make these changes more accessible for experimental analysis, dissociated cell culture and low-light-level video microscopy were used to examine Aplysia sensory neurons in the presence or absence of their target cells. Repeated applications of serotonin, a facilitating transmitter important in behavioral dishabituation and sensitization, produced growth of the sensory neurons that paralleled the long-term enhancement of synaptic strength. This growth required the presence of the postsynaptic motor neuron. Thus, both the structural changes and the synaptic facilitation of Aplysia sensorimotor synapses accompanying long-term behavioral sensitization can be produced in vitro by applying a single facilitating transmitter repeatedly. These structural changes depend on an interaction of the presynaptic neuron with an appropriate postsynaptic target.

Animals↗
PubMed1989

Structural changes vary along individual arterioles in deoxycorticosterone acetate hypertensive rats.

The variability of structural changes along individual arterioles in deoxycorticosterone acetate (DOCA) hypertensive rats was measured by coefficients of variation of: (a) serial lumen diameters along microfil casts of individual mesenteric arterioles; and (b) wall and lumen indices in serial histological cross-sections along individual renal arterioles. The mean lumen diameter of third-order mesenteric arterioles decreased with increasing duration of hypertension. There was increased variability of lumen diameter along lengths of DOCA arterioles, the coefficient of variation at 10 weeks DOCA treatment being 20.2 +/- 0.6% compared to 9.2 +/- 0.2% in controls (P less than 0.001). Medial area to internal elastic lamina (IEL) radius ratio of renal arterioles was increased in DOCA rats compared with control rats (P less than 0.025) and its variability along individual arterioles expressed as the coefficient of variation was 31.70 +/- 3.87% in DOCA rats compared with 15.29 +/- 1.72% in controls (P less than 0.005). The observed increase in variability of lumen diameter and medial area along short lengths of individual arterioles in DOCA hypertensive rats indicates that hypertensive structural changes are probably not directly related to local blood pressure. We suggest that irregular functional vasoconstriction in hypertensive rats could account for this distribution of structural changes.

Animals↗
PubMed1981

[Structural change in neocortical pyramidal neurons in man in the 5th to 9th decade].

The structural changes of cortical pyramids during ageing are consisting in the reversion of the evolution (increasing spine-loss, dendritic atrophy). The spine-loss relates to all ranges of the apical dendrites in like manner. The spine density (number of spines/microm) is an useful parameter for quantitative description of ageing changes in neurons. The structural change of layer V-pyramids begins in several cortical areas in different dates, on an average in the middle of the 7th decade. The process of loss of dendrite spines is not specifically for ageing in sensu strictu, but the result of different damages (transneuronal degeneration according to sensory deprivation, poisons, circulatory disturbances, etc.).

Adult↗
PubMed1994

Electroporation of the photosynthetic membrane: structural changes in protein and lipid-protein domains.

A biological membrane undergoes a reversible permeability increase through structural changes in the lipid domain when exposed to high external electric fields. The present study shows the occurrence of electric field-induced changes in the conductance of the proton channel of the H(+)-ATPase as well as electric field-induced structural changes in the lipid-protein domain of photosystem (PS) II in the photosynthetic membrane. The study was carried out by analyzing the electric field-stimulated delayed luminescence (EPL), which originates from charge recombination in the protein complexes of PS I and II of photosynthetic vesicles. We established that a small fraction of the total electric field-induced conductance change was abolished by N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of the H(+)-ATPase. This reversible electric field-induced conductance change has characteristics of a small channel and possesses a lifetime < or = 1 ms. To detect electric field-induced changes in the lipid-protein domains of PS II, we examined the effects of phospholipase A2 (PLA2) on EPL. Higher values of EPL were observed from vesicles that were exposed in the presence of PLA2 to an electroporating electric field than to a nonelectroporating electric field. The effect of the electroporating field was a long-lived one, lasting for a period > or = 2 min. This effect was attributed to long-lived electric field-induced structural changes in the lipid-protein domains of PS II.

Biophysical Phenomena↗
PubMed1985

UV-induced structural changes in chromatin.

UV-induced structural alterations of chromatin were studied by means of CD, electron microscopic, and gel electrophoretic measurements. The results indicate that chromatin undergoes serious structural changes after irradiation even at very low fluences. In the low fluence range the structural transitions from the higher ordered chromatin structure to the unfolded state occur without detectable changes in the content of histone H1 and of the core histones. Histone H1 disappears only at fluences above 10 kJ/m2. Furthermore, DNA in chromatin is much more sensitive against UV-irradiation and shows a higher degree of strand scission relative to free DNA. While fragmentation in free DNA occurs at fluences above 15 kJ/m2, it occurs even at 5.5 kJ/m2 in the case of chromatin. The biological meaning of the observed UV-induced structural alterations of chromatin is discussed.

Animals↗
PubMed1987

[Functional disorders and structural changes in the liver in Amanita phalloides poisoning].

The liver functional disorders and structural changes were studied in 17 patients (children 6, adults 11, 4 to 70 years of age) with phalloidine intoxication. The clinical course of this severe and lethal exogenic intoxication, its characteristic clinical and laboratory features are discussed in relation to the morphological changes of the liver. The structural changes are similar in all patients independently of their age and the time of death. They are presented by fatty degeneration, acute toxic liver dystrophy and centrilobular necroses. These changes are produced by the specific action of the phalloidine toxins on the liver.

Adolescent↗
PubMed1994

Structural changes in muscle crossbridges accompanying force generation.

We have investigated the structure of the crossbridges in muscles rapidly frozen while relaxed, in rigor, and at various times after activation from rigor by flash photolysis of caged ATP. We used Fourier analysis of images of cross sections to obtain an average view of the muscle structure, and correspondence analysis to extract information about individual crossbridge shapes. The crossbridge structure changes dramatically between relaxed, rigor, and with time after ATP release. In relaxed muscle, most crossbridges are detached. In rigor, all are attached and have a characteristic asymmetric shape that shows strong left-handed curvature when viewed from the M-line towards the Z-line. Immediately after ATP release, before significant force has developed (20 ms) the homogeneous rigor population is replaced by a much more diverse collection of crossbridge shapes. Over the next few hundred milliseconds, the proportion of attached crossbridges changes little, but the distribution of the crossbridges among different structural classes continues to evolve. Some forms of attached crossbridge (presumably weakly attached) increase at early times when tension is low. The proportion of several other attached non-rigor crossbridge shapes increases in parallel with the development of active tension. The results lend strong support to models of muscle contraction that have attributed force generation to structural changes in attached crossbridges.

Adenosine Triphosphate↗
PubMed1980

Structural changes in (Na+ + K+)-ATPase accompanying detergent inactivation.

Structural changes in the purified (Na+ + K+)-ATPase accompanying detergent inactivation were investigated by monitoring changes in light scattering, intrinsic protein fluorescence, and tryptophan to beta-parinaric acid fluorescence resonance energy transfer. Two phases of inactivation were observed using the non-ionic detergents, digitonin, Lubrol WX and Triton X-100. The rapid phase involves detergent monomer insertion but little change in protein structure or little displacement of closely associated lipids as judged by intrinsic protein fluorescence and fluorescence resonance energy transfer. Lubrol WX and Triton X-100 also caused membrane fragmentation during the rapid phase. The slower phase of inactivation results in a completely inactive enzyme in a particle of 400 000 daltons with 20 mol/mol of associated phospholipid. Fluorescence changes during the course of the slow phase indicate some dissociation of protein-associated lipids and an accompanying protein conformational change. It is concluded that non-parallel inhibition of (Na+ + K+)-ATPase and p-nitrophenylphosphate activity by digitonin (which occurs during the rapid phase of inactivation) is unlikey to require a change in the oligomeric state of the enzyme. It is also concluded that at least 20 mol/mol of tightly associated lipid are necessary for either (Na+ + K+)-ATPase or p-nitrophenylphosphatase activity and that the rate-limiting step in the slow inactivation phase involves dissociation of an essential lipid.

Animals↗
PubMed1990

Solutions able to reproduce in vivo surface-structure changes in bioactive glass-ceramic A-W.

High-strength bioactive glass-ceramic A-W was soaked in various acellular aqueous solutions different in ion concentrations and pH. After soaking for 7 and 30 days, surface structural changes of the glass-ceramic were investigated by means of Fourier transform infrared reflection spectroscopy, thin-film x-ray diffraction, and scanning electronmicroscopic observations, in comparison with in vivo surface structural changes. So-called Tris buffer solution, pure water buffered with trishydroxymethyl-aminomethane, which had been used by various workers as a "simulated body fluid," did not reproduce the in vivo surface structural changes, i.e., apatite formation on the surface. A solution, ion concentrations and pH of which are almost equal to those of the human blood plasma--i.e., Na+ 142.0, K+ 5.0, Mg2+ 1.5, Ca2+ 2.5, Cl- 148.8, HCO3- 4.2 and PO4(2-) 1.0 mM and buffered at pH 7.25 with the trishydroxymethyl-aminomethane--most precisely reproduced in vivo surface structure change. This shows that careful selection of simulated body fluid is required for in vitro experiments. The results also support the concept that the apatite phase on the surface of glass-ceramic A-W is formed by a chemical reaction of the glass-ceramic with the Ca2+, HPO4(2-), and OH- ions in the body fluid.

Biocompatible Materials↗
PubMedDate not supplied

[Structural changes in influenza virus RNA during its attenuation].

Changes in structures of only two genes of influenza virus--M and NS genes were found during virus attenuation by the method of oligonucleotide mapping. Such changes were observed in virulent and attenuated viruses (passages 10-23 in chick embryos) by comparing intermediate variants of the virus (passages 11-16 in chick embryos). These results allow us to conclude the important role of these genes in virus attenuation and in connection with virulence of the virus.

Animals↗
PubMed1989

Structural changes in glomeruli and proteinuria in streptozotocin diabetic rats.

In streptozotocin induced diabetes in rats, excretion of urinary protein fractions were studied in relation to structural changes in the renal glomeruli, using light and transmission electron microscopy. After six weeks of induced diabetes only beta 1 and beta 2 plasma globulins were significantly elevated. The amount of excreted proteins and degree of glomerular changes were not proportional. In the initial stages (1-2 weeks) glomerular structural changes were very mild and were accompanied by significantly elevated proteinuria. This progressed (4-8 weeks) to moderate to prominent structural changes with intermittent proteinuria except for the fractions beta 1 & beta 2 which were elevated throughout the duration of the experiment. The amount of proteinuria was not proportional to changes in the plasma protein levels. The following conclusions may be made: 1) The mild early glomerular abnormalities seem to be mainly due to acute metabolic disturbances. 2) An early indication of diabetic nephropathy is provided not only by albuminuria, but may also be an elevated excretion of beta-globulin fractions. 3) Decrease of albuminuria in the later stages of diabetes may be related to the deposition of albumin as a basement membrane-like material in the mesangium.

Animals↗
PubMed1991

19F NMR studies of the D-galactose chemosensory receptor. 2. Ca(II) binding yields a local structural change.

The Escherichia coli D-galactose and D-glucose receptor possesses a Ca(II)-binding site closely related in structure and metal-binding characteristics to the eukaryotic EF-hand sites. Only the structure of the Ca(II)-occupied site is known. To investigate the structural change triggered by Ca(II) and Sr(II) binding, we have used 19F NMR to probe five 5-fluorotryptophan (5F-Trp) and seven 3-fluorophenylalanine (3F-Phe) positions in the structure, extending the approach described in the preceding article. Of particular interest were two 5F-Trp residues near the N terminus of the Ca(II) site at positions 127 and 133. Substitution of the larger Sr(II) for Ca(II) triggered 19F NMR frequency shifts of the 5F-Trp127 and -133 resonances, indicating a detectable structural change in the Ca(II) site. In contrast, the three 5F-Trp resonances from distant regions of the structure exhibited no detectable frequency shifts. When the metal was removed from the Ca(II) site, the 5F-Trp127 and -133 frequencies shifted to a new value similar to that observed for free 5F-Trp in aqueous solvent, and this new frequency was a function of the H2O to D2O ratio, indicating that the residues had become solvent exposed. Metal removal yielded small or undetectable frequency shifts for the three distant 5F-Trp resonances and for four of the five resolved 3F-Phe resonances. The allosteric coupling of the metal and sugar binding sites was observed to be slight: depletion of metal ions was observed to reduce the D-galactose affinity of the receptor by 2-fold. Together the results indicate that the structural changes in the Ca(II) site are primarily localized in the region of the site. Removal of the metal ion from the site exposes the nearby 5F-Trp127 and -133 residues to the solvent, suggesting that the empty site has a more open structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1988

[Effect of structural changes in thyroxine-binding globulin on its biological activity and immunochemical properties].

Using spectroscopic, electrophoretic and microcalorimetric techniques, the changes in the spatial structure of human thyroxine-binding globulin (TBG) induced by exposure of protein solutions to high temperatures (45-90 degrees C) and low pH (2.5-6.0) were studied. Simultaneously the biological activity and immunoreactivity of TBG samples were measured. The structural changes were manifested at 52 degrees C or at pH 4.0 and were then aggravated with a rise in temperature or a decrease of pH. The circular dichroism spectra showed that the molecular ellipticity had a maximum decrease (by 10%) at 218-222 nm. In fluorescence spectra excitable at 280 nm the band half-width increased by 4-6 nm; their intensity decreased by 30-40%, whereas the position of the maxima did not change significantly. After addition of an equimolar amount of thyroxine to inactivated TBG the protein fluorescence was quenched by 25-40%. The electrophoregrams of treated preparations contained additional protein bands possessing no biological activity, whose mobility was less than that of native TBG. Microcalorimetric assays of native TBG revealed a thermoabsorption peak with a maximum at 62.5 degrees C and a half-width of 7.1 degrees C. The thermodynamic parameters of melting of TBG spatial structure were consistent with a model of a two-domain structure of the molecule. The biological activity and immunoreactivity of TBG showed a coordinated decrease with a rise in the degree of protein denaturation, However, the formation of TBG complex with antibodies did not screen the thyroxine-binding center of TBG and did not alter its affinity. Possible mechanisms of structural transition of TBG and its effect on the biological properties of TBG are discussed.

Binding Sites, Antibody↗
PubMed1983

Raman spectroscopic study of age-related structural changes in the lens proteins of an intact mouse lens.

Age-related structural changes in the lens proteins of a normal mouse lens have been monitored in situ by laser Raman spectroscopy. The Raman spectrum of an ICR-strain mouse lens nucleus showed virtually no change in the 550-850- and 900-1800-cm-1 regions as the mouse aged. Lens aging, however, did cause a significant intensity decrease of the Raman band at 880 cm-1 due to tryptophan residues, and the intensity decrease seems to be stepwise. This observation implies that a microenvironmental change of tryptophan residues takes place twice at different places of the lens proteins during normal aging. Particularly striking is that the intensity decrease of the band at 880 cm-1 proceeds in parallel with that of the Raman band at 2579 cm-1 due to a SH stretching mode for the first 4 months. Thus, the first microenvironmental change of tryptophan residues seems to be correlated with the formation of S-S bonds. In contrast to tryptophan residues, no evidence was observed of a microenvironmental change in tyrosine residues. In this respect, the structural changes of lens proteins in aging are sharply distinct from those in lens opacification, in which tyrosine as well as tryptophan residues undergo microenvironmental changes [Itoh, K., Ozaki, Y., Mizuno, A., & Iriyama, K. (1983) Biochemistry 22, 1773-1778]. The relative intensity of the band at 3390 cm-1 due to an OH stretching mode of lens water fell rapidly for the first 4 months and then decreased very gradually. The observation clearly exhibits the process of lens dehydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1976

[Study of structural changes of contractile muscle proteins with the aid of polarization ultraviolet fluorescence microscopy. 1. Conformational changes of F-actin in the muscle fiber caused by ATP and its analogs].

Increase of anisotropy of F-actin fluorescence of balanus and rabbit muscle fibers under the influence of ATP, AMP and pyrophosphate in EGTA presence was detected by means of the polarized ultraviolet (UV) fluorescent microscopy methods. The fluorescence anisotropy changes are assumed to be associated with the conformational changes in the actin. ATP cause more noticeable changes of actin structure, than pyrophosphate and AMP. The conformational changes in the actin of balanus and rabbit muscle fibres were similar. ATP and its analogs induced also decrease of UV fluorescence anisotropy of A-band which appears to be associated with conformational changes in myosin. It was siggested that the changes in fluorescence of anisotropy of A-bands are due to structural changes in both HMM and LMM parts of myosin molecule.

Actins↗
PubMed1976

Rate of quaternary structure change in hemoglobin measured by modulated excitation.

Using a novel technique of modulated photo-dissociation of carbon monoxide from hemoglobin, we have obtained the rates for conversion between the two quaternary states, R, and T, at 3-fold ligation. Our measurements at pH 7 and 22 degrees give rates of 780 +/- 40 sec-1 for going from R to T, and 2500 +/- 200 sec-1 from T to R. This yields an equilibrium constant of 0.31 +/- 0.04, which is in good agreement with previous estimates. The degree of agreement between this equilibrium constant and that predicted from the allosteric model provides a new, quantitative test of the allosteric description. A sequential model for the change in structure was found incompatible with the data, even if kinetic subunit inequivalence was assumed. The technique described here is quite general and can be used as long as the system under investigation can be repetitively excited in a regime in which it responds linearly to the excitation.

Allosteric Regulation↗