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PubMed1986

Crystal structures of modified myoglobins. I. Heme orientation and structural changes around heme in myoglobins reconstituted with isopemptoheme, pemptoheme, 2-ethyldeuteroheme, and 4-ethyldeuteroheme.

The crystal structures of sperm whale metmyoglobins reconstituted with four modified hemes, isopemptoheme, pemptoheme, 2-ethyldeuteroheme, and 4-ethyldeuteroheme, have been determined and refined at 2.2 A resolution to R = 0.217, 0.218, 0.213, and 0.222, respectively. All the crystals of these myoglobins are isomorphous with that of native metmyoglobin. The structural changes of the modified myoglobin from the native myoglobin were examined on difference Fourier maps; the orientation of 4-ethyldeuteroheme in the heme pocket is such that the heme is rotated by 180 degrees about an axis through the alpha-gamma-meso carbons, whereas the orientations of the other three hemes are the same as that of the protoheme in the native myoglobin. The changes of the structures around the heme become greater in the order of isopemptoheme, 2-ethyldeuteroheme less than pemptoheme less than 4-ethyldeuteroheme. The magnitudes of the changes seem to be related to the oxygen affinities of these four reconstituted myoglobins.

Animals↗
PubMed1984

Structural changes of liposome phospholipid packing induced by cytotoxin of the Central Asia cobra venom.

Liposomes and proteoliposomes obtained from rat brain were used; structural changes induced by Vc5 cytotoxin (CT) from Central Asia cobra venom have been studied by the EPR method using spin probes (5-, 10-, or 12-doxylstearic acid). The addition of CT to liposome samples, containing spin probes resulted in the appearance of a new EPR signal in the initial spectrum (samples without CT), typical of probes with strongly retarded mobility. The presence of hydrophobic interaction between the CT molecules and spin labelled fat acids permits the assumption that CT molecules in liposomes trap both lipid probes and phospholipids localized in the reach of action of hydrophobic forces. CT may be supposed to induce formation in membranes of liposomes with domain structures. As a result of hydrophobic interaction with CT molecules both the phospholipid and lipid probe mobility in the domain is substantially less than that in liposome regions free of CT molecules. Due to this, a new signal appears in the initial EPR spectrum of the spin probes. An analysis of the dependence of the probe order parameter value on CT concentration in samples has suggested that CT act uniformly along the membrane lipid profile with a certain CT concentration range. At high concentrations CT molecules cannot penetrate the lipid region deep enough, due to mutual electrostatic repulsion and steric factors at membrane surface. As a result, structural changes involve regions adjacent to the membrane surface only.

Animals↗
PubMed1990

Redox-dependent structure change and hyperfine nuclear magnetic resonance shifts in cytochrome c.

Proton nuclear magnetic resonance assignments for reduced and oxidized equine cytochrome c show that many individual protons exhibit different chemical shifts in the two protein forms, reflecting diamagnetic shift effects due to structure change, and in addition contact and pseudocontact shifts that occur only in the paramagnetic oxidized form. To evaluate the chemical shift differences (delta delta) for structure change, we removed the pseudocontact shift contribution by a calculation based on knowledge of the electron spin g tensor. The g-tensor parameters were determined from the delta delta values of a large set (64) of C alpha H protons at well-defined spatial positions in the oxidized horse protein. The g-tensor calculation, when repeated using only 12 available C alpha H proton resonances for cytochrome c from tuna, proved to be remarkably stable. The largest principal value of the g tensor (gz) falls precisely along the ligand bond between the heme iron and methionine-80 sulfur, while gx and gy closely match the natural heme axes defined by the pyrrole nitrogens. The derived g tensor was then used together with spatial coordinates for the oxidized form to calculate the pseudocontact shift contribution (delta pc) to proton resonances at 400 identifiable sites throughout the protein, so that the redox-dependent chemical shift discrepancy, delta delta-delta pc, could be evaluated. Large residual changes in chemical shift define the Fermi contact shifts, which are found as expected to be limited to the immediate covalent structure of the heme and its ligands and to be asymmetrically distributed over the heme. Smaller chemical shift discrepancies point to a concerted change, involving residues 39-43 and 50-60 (bottom of the protein), and to other changes in the immediate vicinity of the heme ligands. Also, the three internal water molecules are implicated in redox sensitivity. The residues found to change are in good but not perfect agreement with prior X-ray diffraction observations of subangstrom redox-related displacements in the tuna protein. The chemical shift discrepancies observed appear in the main to reflect structure-dependent diamagnetic shifts rather than hyperfine effects due to displacements in the pseudocontact shift field. Although 51 protons in 29 different residues exhibit significant chemical shift changes, the general impression is one of small structural adjustments to redox-dependent strain rather than sizeable structural displacements or rearrangements.

Amino Acid Sequence↗
PubMed1965

The mitotic apparatus. Structural changes after isolation.

The fibrous structure of the mitotic apparatus (MA) isolated from dividing sea urchin eggs undergoes no changes visible in phase contrast during extended storage, but the solubility of the MA rapidly decreases after isolation. Polarization microscopy shows that a decrease in the birefringence of the MA also occurs after isolation and is correlated with the loss of solubility. This loss of birefringence indicates that some structural change takes place during this period, and such a change was demonstrated by means of electron microscopy. The tubular filaments which form the spindle of the intracellular MA and of the freshly isolated MA were found to break down during storage to rows of dense granules, this loss of continuity presumably accounting for the loss of birefringence. The interrelations of the observed changes and the significance of these observations for investigations on the isolated MA are discussed.

Animals↗
PubMed1976

Low resistance junctions in crayfish. Structural changes with functional uncoupling.

Electrical uncoupling of crayfish septate lateral giant axons is paralleled by structural changes in the gap junctions. The changes are characterized by a tighter aggregation of the intramembrane particles and a decrease in the overall width of the junction and the thickness of the gap. Preliminary measurements indicate also a decrease in particle diameter. The uncoupling is produced by in vitro treatment of crayfish abdominal cords either with a Ca++, Mg++-free solution containing EDTA, followed by return to normal saline (Van Harreveld's solution), or with VAn Harreveld's solution containing dinitrophenol (DNP). The uncoupling is monitored by the intracellular recording of the electrical resistance at a septum between lateral giant axons. The junctions of the same septum are examined in thin sections; those of other ganglia of the same chain used for the electrical measurements are studied by freeze-fracture. In controls, most junctions contain a more or less regular array of particles repeating at a center to center distance of approximately 200 A. The overall width of the junctions is approximately 200 A and the gap thickness is 40-50 A. Vesicles (400-700 A in diameter) are closely apposed to the junctional membranes. In uncoupled axons, most junctions contain a hexagonal array of particles repeating at a center to center distance of 150-155 A. The overall width of the junctions is approximately 180 A and the gap thickness is 20-30 A. These junctions are usually curved and are rarely associated with vesicles. Isolated, PTA-stained junctions, also believed to be uncoupled, display similar structural features. There are reasons to believe that the changes in structure and permeability are triggered by an increase in the intracellular free Ca++ concentration. Most likely, the changes in permeability are caused by conformational changes in some components of the intramembrane particles at the gap junctions.

Animals↗
PubMed1986

The kinetic and structural changes of the mitochondrial F1-ATPase with temperature.

Mitochondrial F1-ATPase shows a break in the Arrhenius plot with an increase of the activation energy below 17 degrees C, this may imply that the F1-ATPase undergoes a conformational change at this temperature. Further, a structural change of the F1-ATPase is indicated by analysis of the intrinsic fluorescence at 307 nm between 33 and 11 degrees C and also by evaluation of the circular dichroism spectra of the enzyme at temperatures below and above the temperature corresponding to the discontinuity of the Arrhenius plot. It is therefore suggested that F1-ATPase exists in two temperature dependent conformational states to which different catalytic properties may be assigned.

Adenosine Triphosphate↗
PubMed1980

Structural changes induced by tetracycline in secretory ameloblasts in young rats.

The effects of tetracycline hydrochloride (TC) on secretory ameloblasts in mandibular incisors and first molars in young rats were investigated. The pathogenesis of the TC-induced changes was examined in light and electron microscopes 6, 12, 24 and 96 h after a single intraperitoneal injection of a high dose of TC (200 mg TC/kg body wt.) into 4-d-old animals. Secretory ameloblasts from non-injected animals served as controls. Cellular changes were observed in all teeth 6 h after injection. The changes increased with the postinjection period and after 96 h they were so severe that they were considered irreversible. The incipient changes of the ameloblasts comprised altered structure and location of the mitochondria, succeeded by dilated cisternae of endoplasmic reticulum arranged in short curled formations. Later on, distorted Golgi complexes were observed. Secretory granules appeared in various numbers in the Golgi zone and in the Tomes' processes. In severely affected ameloblasts the cell nuclei showed an increased content of chromatin. Autophagic vacuoles and extracellular membrane bound fragments with cellular remnants were frequent, indicating death of some of the ameloblasts. Areas of stippled secretory material were observed along the formative enamel front and in extracellular spaces between the ameloblasts. In the 96-h group calcified bodies with a varying content of crystals were scattered between the cells. Incisors and the molars displayed similar patterns of structural changes of the secretory ameloblasts; however, the changes developed earlier and became more severe in the molars.

Ameloblasts↗
PubMed1971

Structural changes in Clostridium botulinum type E after treatment with boticin S5 1 .

Treatment with boticin S5(1), a bacteriocin produced by a nontoxigenic organism closely related to Clostridium botulinum type E, caused extensive changes in the structure of a sensitive C. botulinum type E strain. Nucleoid deoxyribonucleic acid, normally seen as fine filaments scattered throughout the cell, was aggregated into dense deoxyribonucleic acid masses. Mesosomes appeared to undergo structural rearrangement from lamellar to vesicular configuration. Eventual dissolution of cell contents left bacterial ghosts composed of seemingly intact cell walls with remnants of the cytoplasmic membrane and internal structures. The morphological changes observed in boticin-treated strain 070 cells were very similar to those produced by a bacteriocin-like substance from phage type 71 Staphylococcus aureus on sensitive beta-hemolytic streptococci. A similarity in the mode of action of the two bactericidal agents is suggested.

Bacteriocins↗
PubMed1985

[Various patterns in structural changes in the cortex and subcortical structures of the human brain during the aging process].

The authors examined the structural organization of cortical and subcortical formations (fields 4, 6, 8, 44, 47, 39, the head of the caudate nucleus and thalamic nuclei) of the right and left hemispheres of the brain of 6 mentally normal subjects aged 30 to 90 years. In sections 20 millimicron thick and stained by Nissl's method the authors measured the density of neurons in subcortical nuclei, in layers III and V of the cortical fields, as well as the number of neurons containing lipofuscin. The identified characteristics indicate heterochronicity of the process of ageing in different portions of the brain: motor and, particularly, cortical structures are involved in this process earlier and more intensively than others.

Adult↗
PubMed1989

[Physiopathology of arterial hypertension. Significance of the renin-angiotensin-aldosterone system and structural changes].

It is presented a review of some recent aspects of the hypertension's physiopathology, namely those related with the renin-angiotensin-aldosterone system and with the cardiovascular structural changes. The large action range of the angiotensin is pointed out, in particular those actions related with the heart's and vessel's adaptation to a chronic load of pressure. In the end, the author stresses some recent references about the genetic's role on the pathogenesis of the structural changes.

Angiotensin II↗
PubMed1990

Regulation and quaternary structural changes in rabbit muscle phosphofructokinase.

Subunit assembly plays a significant role in the regulation of rabbit muscle phosphofructokinase (PFK), although conformational changes and post-translational modifications have also been implicated to regulate the enzyme activity. In the absence of high-resolution structural information, the three-dimensional arrangements of subunits in the rabbit muscle PFK in its active and inactive states are not known. Hence, a systematic study is initiated, and phosphorylation of PFK subunit is employed as a probe for the structure-function correlation of the enzyme. The self-association of the phosphorylated and dephosphorylated PFK was monitored by sedimentation velocity at pH 7.0 and 23 degrees C. Results show that both the phosphorylated and dephosphorylated forms of PFK exhibit the same mechanism of assembly. The secondary structures of both forms of PFK were monitored by circular dichroism (CD) as a function of protein concentration ranging from 20 to 2000 micrograms/ml. Results show that there is no detectable difference in the structure under all experimental conditions. The accessibility of tryptophan to solvent was monitored by fluorescence quenching within the same range of protein concentration. Results show that the fluorophores are more accessible to the quencher at higher protein concentrations. Hence, post-translational modification and subunit association do not induce significant structural change in PFK subunit, although the accessibility of tryptophan residues is altered with oligomer formation. Furthermore, sedimentation and CD studies show that the activation of PFK by substrate includes no detectable modification in secondary/tertiary structure but a quaternary structural change, and the local environments of some, if not all, of the tryptophan residues are less accessible to solvent. Hence, the change in sedimentation behavior between the active and inactive tetrameric PFK is due to a rearrangement of subunit-subunit interactions. In order to correlate the physical properties of PFK to the regulatory behavior of enzyme activity, the steady-state kinetics were investigated under the same experimental conditions. In conditions where enhancement of self-association is observed, the kinetic behavior reflects activation of the enzyme. Hence, this correlation between subunit assembly and the regulation of enzyme activity in PFK must reflect an intrinsic property of the muscle enzyme.

Animals↗
PubMed1986

Financing reform and structural change in the health services industry.

This paper reviews the major trends in financing reform, emphasizing their impact on those characteristics of the market for health services that economists have viewed as monopolistic, and discusses the implications of structural change for the allied health professions. Hopefully, by understanding the fundamental forces of change and responding to uncertainty with flexibility and imagination, the allied health professions can capitalize on the opportunities afforded by structural change. Overall, these trends should result in the long-term outlook for use of allied health services to increase at an average annual rate of 9% to 10%. Allied health professionals may also witness an increase in independent practice opportunities. Finally, redistribution of jobs will likely occur in favor of outpatient facilities, home health agencies, and nontraditional settings. This in turn will have an impact on allied health education, which will need to adapt to these types of reforms.

Allied Health Personnel↗
PubMedDate not supplied

Potent V2 vasopressin antagonists with structural changes at their C-terminals.

A variety of structural changes were made in the C-terminals of four potent antidiuretic (V2) antagonists. The parent analogs were all derivatives of [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid)]arginine-vasopressin, d(CH2)5AVP, namely d(CH2)5[D-Phe2,Ile4]AVP, d(CH2)5[D-Ile2,Ile4]AVP, d(CH2)5[D-Tyr(Et)2, Val4]AVP and d(CH2)5[D-Tyr(Et)2,Ile4]AVP. A number of amino acid amides were substituted for the C-terminal 9-glycinamide without reducing their V2-antagonistic potencies in rats. Many non-amino acid structures were also tolerated at the C-terminals of these antagonists and this end of these peptides can be prolonged without interfering with antagonistic potencies. Such altered V2-antagonists may be useful for the development of radioactive ligands, affinity labels and in affinity columns for studies on antidiuretic receptors. These C-terminal modifications also provide useful information for the further development of potent and specific V2-antagonists which can be valuable pharmacological tools and also promise to become useful clinically for the treatment of excessive water retention.

Animals↗
PubMedDate not supplied

[Structural changes in Candida lipolytica cells during citric acid biosynthesis].

The techniques of light and electron microscopy were used to study structural changes in Candida lipolytica cells related to limitation of their growth and a nitrogen source in medium with glucose and hexadecane and transition of the culture to the production of citric acids. Changes in the content of protein in the cell and in the activities of enzymes of the citrate and glyoxylate cycles located in mitochondria and peroxysomes of the yeast were investigated at the same time. The results characterizing cytological changes in the cell of C. lipolytica in the conditions of citric acid biosynthesis fit in well with the data on protein content and enzyme activities in the cells obtained by biochemical analysis. The transition of the yeast cells to the overproduction of citric acids has been shown to be related to profound rearrangements of the cell: the inhibition of protein synthesis; changes in the structure of the cytoplasm; the appearance of vacuoles of an irregular shape, often in contact with the mitochondria; changes in the mitochondrial and peroxysomal apparatus; the accumulation of lipids. It has been demonstrated once again that the peroxysomal apparatus of the yeast cell has a relationship with the metabolism of n-alkanes.

Candida↗
PubMed1982

Functional and structural changes in veins in spontaneous hypertension.

Six month old spontaneously hypertensive rats (SHR) and age and sex matched normotensive Wistar-Kyoto rats (WKY) were examined to evaluate the existence of functional and structural changes in the portal vein (PV), inferior vena cavae (IVC) and pulmonary arteries (PA). PV, central nervous and systolic right ventricular pressures did not differ in the anesthetized SHR when compared with WKY, despite elevated systolic arterial pressure. PV, IVC and PA obtained from SHR were less extensible, developed more tension, exhibited an enhanced sensitivity to serotonin and a thromboxane-like prostanoid, accumulated more of the protein precursors 2-14C-leucine, 2-14C-glucosamine, 7-3H-fucose, exhibited a normal rate of uptake of 2-14C-thymidine, and increased protein content and a decreased concentration of DNA. When examined under light and electron microscopy, the veins and PA obtained from SHR demonstrated medial smooth muscle hypertrophy, and increased density of PAS-Schiff positive stain, enlarged and prominent Golgi apparati and an increased cell diameter through the region of the nucleus. These changes were not due to water-logging since the water content of the veins and PA from SHR and WKY did not differ. These data support the conclusion that PV, IC and PA obtained from SHR exhibit functional and structural changes independent of increases in intravenous pressure. These changes may relate to the increase in blood vessel protein.

Animals↗
PubMed1992

Structural changes and enhancements in DNase I footprinting experiments.

In footprinting experiments, an increase in DNA cleavage with addition of ligand to a system may be due to a ligand-induced structural change. Ligand binding also enhances cleavage by displacing the cleavage agent from ligand-binding sites, thus increasing its concentration elsewhere. The theory and characteristics of this mass-action enhancement are given, and it is shown how it may be recognized. Results of DNase I footprinting of small oligomers, with actinomycin D as ligand, are analyzed to reveal which enhancements are due to mass action, and which can reasonably be ascribed to structural changes. Patterns in the footprinting plots from our experiments on actinomycin D binding to a 139-base-pair DNA fragment (with DNase I as a probe) are studied in the same way. The likely origins of these patterns are discussed, as are enhancements occurring with other probes commonly used in footprinting experiments.

Base Sequence↗
PubMed1992

Glomerular structural changes in type 1 (insulin-dependent) diabetes mellitus: causes, consequences, and prevention.

Diabetic nephropathy is caused primarily by advanced glomerulopathy, the renal expression of diabetic microangiopathy. With stereological methods a quantitative description of the structural changes is achieved. The glomerulopathy is characterized by an increase in basement membrane material: thickening of the capillary wall and an increase in mesangial volume relative to glomerular volume, comprising increase in matrix. Among groups of patients conformity between renal function stage and structure exists. The parameters measuring glomerulopathy are normal at the onset of diabetes; patients with normoalbuminuria may show slight basement membrane thickening, or normal parameters; the microalbuminuric group shows a measurable, but moderate glomerulopathy; patients with overt nephropathy have advanced lesions; at this stage heterogeneity among glomeruli makes the estimates weaker. Recent data indicate that the changes in peripheral basement membrane and in mesangial matrix develop in concert and both contribute to the early stage of glomerulopathy in patients with microalbuminuria. As to the consequences of the structural changes the mechanism of albuminuria is not clear. It is suggested that the early glomerulopathy entails other structural modifications, including formation of new vessels which may be the site of leakage. The marked deviations in glomerular filtration rate correspond well with estimates of filtration surface area: in the early hyperfunction state it is increased; in advanced nephropathy it is decreased, due to advanced glomerulopathy in conjunction with glomerular occlusion. The diabetic state is the necessary condition for the glomerulopathy. In relating structural changes to presumed contributing causes no supporting evidence of a relationship with glomerular hyperfunction or hypertrophy was observed. The structural parameters may be useful tools in clinical trials aiming at arresting the development of glomerulopathy, and thereby providing a prevention of diabetic nephropathy.

Diabetes Mellitus, Type 1↗