PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Structural analysis”

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 217 records · Page 12Linked to original sources
PubMed1992

Medical knowledge for clinical problem solving: a structural analysis of clinical questions.

Despite technological advances that support wide-ranging access to and transfer of knowledge, practicing physicians continue to underutilize current biomedical literature. This paper explores the nature of clinically applicable medical knowledge through a structural analysis of clinical questions. The author analyzed a set of sixty questions, based on actual online search requests of practicing physicians, for stated and unstated needs, certainty levels, implicit and explicit assumptions, decision-making processes, and type of answer required. As a result, four states of information valuable in patient care were identified: prediagnostic assessment, diagnosis, treatment choice, and learning. These states are presented in frame-like structures that integrate declarative and procedural components of medical decision making. It is concluded that clinical problem solving requires a blend of declarative and procedural knowledge. The ratio depends, in part, upon the reasoning process underway at the time of the request. Procedural knowledge required for clinical problem solving may be absent from current biomedical journal literature or difficult to identify.

Decision Making↗
PubMed1991

Structural analysis of phospholipase A2 by near-IR Fourier transform Raman spectroscopy.

Venom toxins were isolated from Formosan cobra (Naja naja atra) by cation-exchange chromatography. Most toxin components could be obtained in relatively pure forms by single-step ion-exchange chromatography whereas an extra step of gel permeation was needed for the separation of phospholipase A2 (PLA2) from the major neurotoxic component, i.e. cobrotoxin. The newer near-IR FT-Raman analytical method has been applied to the characterization of PLA2 in their lyophilized forms. Structural analysis of PLA2 and correlation of Raman spectroscopic data with amino acid compositions were made. The results indicate that phospholipase A2 showed the Raman peak at 1659 cm-1 which is characteristic of the alpha-helical structure in this enzyme. It is also found that the relative Raman signal intensities of Tyr, Phe, Trp and Met residues in purified toxins correlate very well with the structural data obtained from amino acid analysis. The application of near-IR FT-Raman techniques in the detection of the microenvironments of the aromatic amino acids such as Tyr and Trp in the native toxins may prove useful in the investigation of the functional properties of various venom toxins.

Amino Acids↗
PubMed1993

Psychological and behavioral consequences of job loss: a covariance structure analysis using Weiner's (1985) attribution model.

B. Weiner's (1985) attribution model of achievement motivation and emotion was used as a theoretical foundation to examine the mediating processes between involuntary job loss and employment status. Seventy-nine manufacturing employees were surveyed 1 month prior to permanent displacement, and finding another job was assessed 18 months later. Covariance structure analysis was used to evaluate goodness of fit and to compare the model to alternative measurement and structural representations. Discriminant validity analyses indicated that the causal dimensions underlying the model were not independent. Model predictions were supported in that internal and stable attributions for job loss negatively influenced finding another job through expectations for re-employment. These predictions held up even after controlling for influential unmeasured variables. Practical and theoretical implications are discussed.

Adaptation, Psychological↗
PubMed1993

The MotA protein from bacteriophage T4 contains two domains. Preliminary structural analysis by X-ray diffraction and nuclear magnetic resonance.

Controlled protease cleavage experiments and N-terminal sequence analyses were used to show that the transcriptional activator MotA from bacteriophage T4 has a two-domain structure. The N and C-terminal domains have M(r) values of 10,300 and 11,800, respectively, and were separately cloned and overexpressed in Escherichia coli. One and two-dimensional NMR spectroscopy indicate that both domains have stably folded structures and contain extensive secondary structure. The N-terminal domain is substantially alpha-helical, whereas the C-terminal domain has a high content of beta-strand. The N-terminal domain has been crystallized under three different conditions, all with the space group P3(1(2))21 and similar unit cell dimensions. The best crystals are grown from ammonium sulfate, have cell dimensions a = b = 46.7 A, c = 139.6 A, and diffract to beyond 2.4 A. The high quality of the NMR and diffraction data will allow a complete structural analysis of MotA by a combination of these techniques.

Bacteriophage T4↗
PubMed1980

Crossed immunoelectrophoresis and chemical structural analysis used for characterization of two varieties of Escherichia coli K2 polysaccharide antigen.

Crossed immunoelectrophoresis has shown that the Escherichia coli polysaccharide K2 antigen exists in two forms, K2ab and K2a. In confirmation of this finding, chemical structural analysis showed that K2ab, in addition to the galactose, glycerol and phosphate groups common to K2ab and K2a, contained 0 acetyl groups. The contrast between the earlier and the present K2 designation is discussed and the superiority of the CIE technique for this type of analysis is underlined.

Escherichia coli↗
PubMed2000

Structural analysis of glycosaminoglycans in Drosophila and Caenorhabditis elegans and demonstration that tout-velu, a Drosophila gene related to EXT tumor suppressors, affects heparan sulfate in vivo.

We have devised a sensitive method for the isolation and structural analysis of glycosaminoglycans from two genetically tractable model organisms, the fruit fly, Drosophila melanogaster, and the nematode, Caenorhabditis elegans. We detected chondroitin/chondroitin sulfate- and heparan sulfate-derived disaccharides in both organisms. Chondroitinase digestion of glycosaminoglycans from adult Drosophila produced both nonsulfated and 4-O-sulfated unsaturated disaccharides, whereas only unsulfated forms were detected in C. elegans. Heparin lyases released disaccharides bearing N-, 2-O-, and 6-O-sulfated species, including mono-, di-, and trisulfated forms. We observed tissue- and stage-specific differences in both chondroitin sulfate and heparan sulfate composition in Drosophila. We have also applied these methods toward the analysis of tout-velu, an EXT-related gene in Drosophila that controls the tissue distribution of the growth factor Hedgehog. The proteins encoded by the vertebrate tumor suppressor genes EXT1 and 2, show heparan sulfate co-polymerase activity, and it has been proposed that tout-velu affects Hedgehog activity via its role in heparan sulfate biosynthesis. Analysis of total glycosaminoglycans from tout-velu mutant larvae show marked reductions in heparan sulfate but not chondroitin sulfate, consistent with its proposed function as a heparan sulfate co-polymerase.

Animals↗
PubMed1990

Isolation and structural analysis of three new disialylated oligosaccharides from human milk.

Five disialylated oligosaccharides, of which three were new compounds, were isolated from pooled human milk. The isolation procedure included gel filtration and ion-exchange chromatography and the final purification was accomplished by HPLC using a mobile phase containing triethylamine as an ion-pairing reagent. Structural analysis was carried out by chemical analyses, fast atom bombardment mass spectrometry, and 500-MHz NMR spectroscopy. The following new structures were found: (formula; see text).

Carbohydrate Conformation↗
PubMed1976

Structural analysis of phosphatidylcholines of Yoshida ascites hepatoma and liver cells from host rats fed a control and an essential fatty acid-deficient diet.

In order to study the effect of a dietetic manipulation on the phospholipid molecular structure of a poorly differentiated tumor, the phosphatidylcholines from Yoshida hepatoma cells (AH130) grown either in essential fatty acid deficient or control rats were analyzed comparatively to those from the host livers. Due to essential fatty acid deficiency, the host rat liver exhibited an increased level of mono-unsaturated 1,2-diacyl-sn-glycero-3-phosphocholines, a reduced level of the species contained linoleic acid, and the substitution of tetra- and polyunsaturated-1,2-diacyl-sn-glycero-3-phosphocholines with equivalent amounts of species containing eicosatrienoic acid. The structural analysis of the phosphatidylcholines from Yoshida hepatoma cells grown either in control or essential fatty acid deficient rats revealed the occurrence of 1-alkyl-2-acyl- together with 1,2-diacyl-sn-glycero-3-phosphocholines. The alkyl chains of ether-linked phosphatidylcholines were mainly constituted by 18 : 1, while the acyl chains were characterized by a high level of linoleic and arachidonic or eicosatrienoic acids. The 1,2-diacyl-sn-glycero-3-phosphocholines of the Yoshida hepatoma cells grown in control rats, when compared to those of the liver, showed a higher level of 1,2-disaturated, an increased proportion of mono-unsaturated and a lower proportion of tetra- and polyunsaturated species. In addition, the hepatoma cells showed the occurrence of high proportions of reverse isomeric and random species, such as 1-oleoyl-2-palmitoyl-, 1,2-dioleoyl-, 1-oleoyl-2-linoleoyl- and 1-linoleoyl-2-oleoyl-sn-glycero-3-phosphocholines, scarcely represented in the liver. Growth of Yoshida hepatoma cells in essential fatty acid deficient rats resulted in :(i) the disappearence of 1,2-diacyl-sn-glycero-3-phosphocholines containing linoleic acid; (ii) the substitution of tetra- and and polyunsaturated 1,2-diacyl-sn-glycero-3-phosphocholines with small quantities of species containing eicosatrienoic acid; (iii) an increase of of monounsaturated species, mainly 1-stearoyl-2-oleoyl- and 1-palmitoyl-2-palmitoleoyl-sn-glycero-3-phosphocholines; (iv) a remarkable increase of 1,2-dioleoyl-sn-1,2-dioleoyl-sn-glycero-3-phosphocholine.

Animals↗
PubMed1979

The CAN1 locus of Saccharomyces cerevisiae: fine-structure analysis and forward mutation rates.

A system of strains and growth media was developed to allow efficient detection of forward mutation, reversion, complementation, and suppression at the canavanine-resistance (CAN1) locus of Saccharomyces cerevisiae. Genetic fine-structure analysis revealed that the map length is at least 40, and possibly as much as 60 X-ray map units; this is the longest gene map yet reported in S. cerevisiae. Allelic complementation was not observed, despite testing of a large number of allele pairs, and alleles suppressible by the ochre suppressor SUP11 were absent from a sample of 48 spontaneous mutants and occurred infrequently (7%) among a sample of ultraviolet-induced mutants. Infrequent mutant types included canavanine-resistant mutants capable of arginine uptake and alleles thought to represent deletions or inversions. In contrast to previous reports in the literature, the spontaneous forward mutation rate at CAN1 did not increase during meiosis.

Alleles↗
PubMed1993

The problem of equivalent models in applications of covariance structure analysis.

For any given covariance structure model, there will often be alternative models that are indistinguishable from the original model in terms of goodness of fit to data. The existence of such equivalent models is almost universally ignored in empirical studies. A study of 53 published applications showed that equivalent models exist routinely, often in large numbers. Detailed study of three applications showed that equivalent models may often offer substantively meaningful alternative explanations of data. The importance of the equivalent model phenomenon and recommendations for managing and confronting the problem in practice are discussed.

Analysis of Variance↗
PubMed2000

Mechanisms for the enhanced thermal stability of a mutant of transcription factor 1 as explained by (1)H, (15)N and (13)C NMR chemical shifts and secondary structure analysis.

A variant of the bacteriophage SPO1-encoded transcription factor 1 (TF1) with two site-specific mutations (E15G and T32I) was shown to be more thermally stable and bind DNA more tightly compared to the wild-type protein. In order to understand the biochemical mechanisms underlying these properties, we are engaged in determining the solution structures of this mutant alone and in complex with DNA using nuclear magnetic resonance (NMR) spectroscopy. The first phase of this project is reported here, as we have completed most of the backbone and sidechain sequential NMR assignments of the mutant protein, TF1-G15/I32. Insights derived from the (1)H, (15)N and (13)C chemical shifts and from the secondary structure analysis provide us with an explanation for the noted increase in thermal stability of TF1-G15/I32. Compared to the structure of the wild-type protein, the beta-sheet and the C-terminal helix remain largely unaffected whereas the mutations cause great changes in the first two helices and their enclosed loop. Specifically, we have found that the second helix is extended by one residue at its N-terminus and rotated in a way that allows Ala-37 to interact with Tyr-94 of the C-terminal helix. The loop has been found to become more rigid as a result of hydrophobic interactions between the flanking second and first helices and also between the second helix and the loop itself. Furthermore, the T32I mutation allows tighter packing between the second helix and the beta-sheet. Collectively, these changes contribute to a more tightly associated dimer and hence, to a greater thermal stability.

DNA-Binding Proteins↗
PubMed1981

Structural dimorphism of bile salt/lecithin mixed micelles. A possible regulatory mechanism for cholesterol solubility in bile? X-ray structure analysis.

The three-dimensional structure of bile salt/lecithin mixed micelles in 0.15 M saline was derived from X-ray small-angle scattering measurements under various conditions. Two essentially different types of micelles were detected. At bile salt:lecithin molar ratios lower than approximately 2:1, lamellar particles similar to a lecithin bilayer arrangement were found. The thickness of the bilayer is 5.1 nm for mixed micelles having a molar ratio of 1:1. The lateral dimensions of the micelle were found strongly dependent upon molar ratio, increasing as lecithin content increases. In addition, it appeared that under certain incompletely defined conditions vesicular particles having diameters in the region of more than 100 nm occur. A molecular model of this type of micelle has been derived by means of a thorough interpretation of the electron density distribution across the plane of the bilayer. This model is generally consistent with the "mixed-disk" model of Mazer et al. [Mazer, N. A., Kwasnick, R. F., Carey, M. C., & Benedek, G. B. (1977) Micellization, Solubilization, Microemulsions, Proc. Int. Symp. 1, 383-402] and thus differs from that proposed by Small [Small, D. M. (1967) Gastroenterology 52,607-610] and Dervichian [Dervichian, D. G. (1968) Adv. Chem. Ser. No. 84, 78-87]. At molar ratios exceeding 2:1, a different type of micelle structure was found. This is a highly isometrical particle of globular shape, probably having a centrosymmetric arrangement of the molecular constituents. At a 3:1 bile salt:lecithin molar ratio, the mean physiological ratio for human gallbladder bile, the diameter of this micelle is 6.2 nm. Provided that other bile constituents have no significant influence on the structure, it may reasonably be expected that native gallbladder bile contains micelles of this latter type. The prevalent balance between the two micellar forms may thus regulate the capacity of bile to transport cholesterol.

Bile Acids and Salts↗
PubMed1982

Virion DNA of ground squirrel hepatitis virus: structural analysis and molecular cloning.

The structure of the encapsidated DNA genome of ground squirrel hepatitis virus (GSHV) has been examined by restriction endonuclease cleavage, nucleic acid hybridization, and molecular cloning. GSHV virion DNA is a relaxed circular molecule of approximately 3,200 bases in length; most molecules harbor an extensive single-stranded region which is largely confined to one-half of the genome. The full-length viral DNA strand is covalently bound to protein. The single-stranded region can be repaired in vitro by the action of the endogenous virion polymerase, exogenously added DNA polymerase from avian myeloblastosis virus, or both. Restriction enzyme cleavage of viral DNA from different isolates demonstrated that multiple variants of GSHV exist in nature. The genomes of two such strains have been cloned in Escherichia coli, and their physical maps have been determined. Nucleic acid hybridization studies revealed that the strains share sequence homology with the DNA of human hepatitis B virus. Regions homologous to the coding regions for the surface and core antigens of human hepatitis B virus have been localized on the GSHV chromosome. Molecular cloning experiments have also led to the identification of a region of the viral genome which is altered in a procaryotic host.

Animals↗
PubMed2000

New crystal forms and low resolution structure analysis of 20S proteasomes from bovine liver.

20S proteasomes from higher eukaryotes have immunological functions rather than those from archibacteria or yeast. To clarify the mechanism of the sorting and production of antigen-presenting peptides, it is important and worthwhile to determine the structure of mammalian proteasomes using a third generation synchrotron radiation source. Here we report new crystal forms of 20S proteasomes from bovine liver and preliminary structure analysis of them. The crystals belong to the same space group but have different cell dimensions. One crystal (form I) belongs to space group P2(1)2(1)2(1) with unit cell dimensions of a = 124.8, b =197.4, c =323.8 A, and diffracts to 3.0 A resolution. The other crystal (form II) belongs to the same space group with a =115.1, b =205.6, c =316. 0 A, and diffracts to 4.0 A resolution. The diffraction data for the form I crystal provided an interpretable electron density map for presenting the structural differences from yeast proteasomes.

Animals↗
PubMed1996

Structural analysis of families with a polydrug-dependent, bulimic, or normal adolescent daughter.

This study compared perceived relationships and interaction patterns among 44 families with externalizing (polydrug-dependent), internalizing (bulimic), or normal adolescent daughters. Data from L.S. Benjamin's (1974) structural analysis of social behavior rating scales and observational coding system were subjected to a pattern analysis of effect sizes. Results revealed that families of polydrug-dependent girls were less well attached and less autonomous than were families of daughters with bulimia who were, in turn, less attached and autonomous than controls. Observed interactions also showed that parents of drug-dependent teenagers communicated a mixed message of blaming the daughter while pseudo-affirming her. The findings were interpreted as evidence for specific disturbances in the critical elements of attachment and autonomy in both clinical disorders, with more pronounced and pervasive problems in the families of polydrug-dependent girls.

Adolescent↗
PubMed1999

Structural analysis at 2.2 A of orthorhombic crystals presents the asymmetry of the allophycocyanin-linker complex, AP.LC7.8, from phycobilisomes of Mastigocladus laminosus.

An electrophoretically purified allophycocyanin-linker complex, AP. LC7.8, from phycobilisomes of Mastigocladus laminosus has been crystallized in the orthorhombic space group P212121. Cryocrystallographic x-ray measurements enabled the structural analysis of the complex at a resolution of 2.2 A. The asymmetric unit contains two side-to-side associated "trimeric" (alphabeta)3 allophycocyanin complexes comprising the linker polypeptide in a defined orientation inside the trimer. The linker representing a protein fold related to the prosegment of procarboxypeptidase A is in contact with only two of the three beta-subunits and directly interacts with the corresponding chromophores of these proteins. In addition to a modulation of the chromophores' spectral properties, the linker polypeptide attracts the alphabeta-subcomplexes, thereby bringing the beta-chromophores closer together. These results will enable interpretations of energy-transfer mechanisms within phycobiliproteins.

Amino Acid Sequence↗
PubMed1991

Evaluating measurement models in clinical research: covariance structure analysis of latent variable models of self-conception.

Indirect measures of psychological constructs are vital to clinical research. On occasion, however, the meaning of indirect measures of psychological constructs is obfuscated by statistical procedures that do not account for the complex relations between items and latent variables and among latent variables. Covariance structure analysis (CSA) is a statistical procedure for testing hypotheses about the relations among items that indirectly measure a psychological construct and relations among psychological constructs. This article introduces clinical researchers to the strengths and limitations of CSA as a statistical procedure for conceiving and testing structural hypotheses that are not tested adequately with other statistical procedures. The article is organized around two empirical examples that illustrate the use of CSA for evaluating measurement models with correlated error terms, higher-order factors, and measured and latent variables.

Analysis of Variance↗