Search PubMed⌕ Search

Biomedical subjects

S L Edwards

Publications and source records attributed to S L Edwards.

At least 55 records · Page 3Linked to original sources
PubMed1994

The driver's license list as a population-based sampling frame in Iowa.

Driver's license lists are infrequently used for population-based sampling, presumably because of suspicions of poor population coverage. The 1990 Iowa driver's license list was compared with the 1990 census to evaluate coverage by 5-year age group, sex, resident county, and urbanicity. Coverage exceeded 90% among 15- to 74-year-old men and 15- to 64-year-old women, with uniform coverage by county and county urbanicity group in these age ranges. In Iowa, these lists are convenient and cost-effective and appear to be representative for 25- to 64-year-olds. The representativeness of driver lists in regard to other factors and in other geographic regions deserves further evaluation.

Adolescent↗
PubMed1993

The distribution of nitric oxide synthase-containing autonomic preganglionic terminals in the rat.

Nitric oxide synthase (NOS)-immunoreactivity was co-localised with NADPH diaphorase activity in preganglionic sympathetic neurons and in their terminals in pre- and paravertebral sympathetic ganglia. The density of NOS-containing terminals varied between ganglia. Reactive terminals were densest in the superior cervical, stellate and inferior mesenteric ganglia, where the majority of the neurons were surrounded by reactive fibres, and the coeliac and superior mesenteric ganglia, where about half the postganglionic somata were surrounded by reactive terminals. Fibres were least abundant in the pelvic ganglia and thoracic and lumbar sympathetic chain ganglia. NOS reactivity did not coincide with the distribution of calcitonin gene related peptide immunoreactivity, a marker for the terminals of NOS-containing sensory neurons in the rat. The distribution of nerve cells and terminals suggests that NOS is present in more than one functional subpopulation of sympathetic preganglionic neurons.

Amino Acid Oxidoreductases↗
PubMed1993

Crystallographic refinement of lignin peroxidase at 2 A.

The crystal structure of the major lignin peroxidase isozyme from Phanerocheate chrysosporium has been refined to an R = 0.15 for data between 8 A and 2.03 A. The refined model consists of 2 lignin peroxidase molecules in the asymmetric unit, 2 calcium ions per monomer, 1 glucosamine per monomer N-linked to Asn-257, and 476 water molecules per asymmetric unit. The model exhibits excellent geometry with a root mean square deviation from ideality in bond distances and angles of 0.014 A and 2.9 degrees, respectively. Molecule 1 consists of all 343 residues, while molecule 2 consists of residues 1-341. The overall root mean square deviation in backbone atoms between the 2 molecules in the asymmetric unit is 0.36 A. The refinement at 2.0 A confirms our conclusions based on the partially refined 2.6-A structure (Edwards, S. L., Raag, R., Wariishi, H., Gold, M. H., and Poulos, T. L. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 750-754). The overall fold of lignin peroxidase closely resembles that of cytochrome c peroxidase. A superimposition of alpha-carbons gives a root mean square deviation of 2.65 A between the two peroxidases and 1.66 A for the helices. The active sites also are similar since both contain a proximal histidine heme ligand hydrogen-bonded to a buried aspartate residue and both contain histidine and arginine residues in the distal peroxide binding pocket. The most obvious difference in the active site is that whereas cytochrome c peroxidase has tryptophan residues located in the proximal and distal heme pockets, lignin peroxidase has phenylalanines. There are four other especially noteworthy differences in the two structures. First, although the heme in cytochrome c peroxidase is recessed about 10 A from the molecular surface, the heme pocket is open to solvent. The analogous opening in lignin peroxidase is smaller which can explain in part the differences in reactivity of the two hemes. This same opening may provide the site for binding small aromatic substrates. Second, lignin peroxidase has a carboxylate-carboxylate hydrogen bond important for heme binding that is not present in cytochrome c peroxidase. Third, lignin peroxidase contains 2 structural calcium ions while cytochrome c peroxidase contains no calcium. The calciums in lignin peroxidase coordinate to residues near the C-terminal ends of the distal and proximal helices and hence are probably important for maintaining the integrity of the active site. Fourth, the extra 49 residues in lignin peroxidase not present in cytochrome c peroxidase constitutes the C-terminal end of the molecule with the C terminus situated at the "front" end of the molecule between the two heme propionates.

Binding Sites↗
PubMed1993

Crystal structure of lignin peroxidase.

The crystal structure of lignin peroxidase (LiP) from the basidiomycete Phanerochaete chrysosporium has been determined to 2.6 A resolution by usine multiple isomorphous replacement methods and simulated annealing refinement. Of the 343 residues, residues 3-335 have been accounted for in the electron density map, including four disulfide bonds. The overall three-dimensional structure is very similar to the only other peroxidase in this group for which a high-resolution crystal structure is available, cytochrome c peroxidase, despite the fact that the sequence identity is only approximately 20%, LiP has four disulfide bonds, while cytochrome c peroxidase has none, and LiP is larger (343 vs. 294 residues). The basic helical fold and connectivity defined by 11 helical segments with the heme sandwiched between the distal and proximal helices found in cytochrome c peroxidase is maintained in LiP. Both enzymes have a histidine as a proximal heme ligand, which is hydrogen bonded to a buried aspartic acid side chain. The distal or peroxide binding pocket also is similar, including the distal arginine and histidine. The most striking difference is that, whereas cytochrome c peroxidase has tryptophans contacting the distal and proximal heme surfaces, LiP has phenylalanines. This in part explains why, in the reaction with peroxides, cytochrome c peroxidase forms an amino acid-centered free radical, whereas LiP forms a porphyrin pi cation radical.

Journal Article↗
PubMed1993

Subunit b of cholera toxin labels interstitial cells of Cajal in the gut of rat and mouse.

Cholera toxin subunit b was found in vivo and in vitro to label interstitial cells of Cajal in the intestine of rat and mouse. Cholera toxin-labelled interstitial cells were present in the subserosa, the myenteric plexus and the deep muscular plexus of mouse small intestine, and the deep muscular plexus only of the rat small intestine. In the large intestine of the mouse, interstitial cells were present in the subserosa and in a plexus associated with the inner surface of the circular muscle, while in the rat they were only present in the latter location. Macrophages, which were present in many of the same locations as interstitial cells, were also labelled by cholera toxin but could be distinguished from interstitial cells by their ability to take-up fluorescein isothiocyanate-labelled dextran. Labelling with subunit b of cholera toxin is a simple way of labelling interstitial cells of Cajal and which is compatible with a range of physiological and histological procedures.

Animals↗
PubMed1992

Using the Mead model as a framework for nursing care.

A model of nursing has no valid purpose unless it serves nurses to help make their nursing better (Fawcett, 1989). The Mead model formed the basis for nursing care of Jason, a young patient who sustained a head injury, a puncture wound and lacerations to his face, in the study presented here. Examination of the Mead Model of nursing is followed by an account of why this model was used in preference to others as a framework for Jason's care. Three components of his nursing care--wound care, communication, involvement of relatives--are discussed in relation to both the model and current knowledge. It was concluded that as a structured way of planning and giving care, the Mead model lacks adequate guidelines. A less experienced nurse using the Mead model may overlook certain aspects of care, an experienced nurse may use his/her knowledge to give high standard care using research-based information. However, models need to be tested so they may be rejected or modified as guidelines for care in this case in the United Kingdom, within a welfare-orientated society.

Adolescent↗
PubMed1990

X-ray structures of recombinant yeast cytochrome c peroxidase and three heme-cleft mutants prepared by site-directed mutagenesis.

The 2.2-A X-ray structure for CCP(MI), a plasmid-encoded form of Saccharomyces cerevisiae cytochrome c peroxidase (CCP) expressed in Escherichia coli [Fishel, L.A., Villafranca, J. E., Mauro, J. M., & Kraut, J. (1987) Biochemistry 26, 351-360], has been solved, together with the structures of three specifically designed single-site heme-cleft mutants. The structure of CCP(MI) was solved by using molecular replacement methods, since its crystals grow differently from the crystals of CCP isolated from bakers' yeast used previously for structural solution. Small distal-side differences between CCP(MI) and bakers' yeast CCP are observed, presumably due to a strain-specific Thr-53----Ile substitution in CCP(MI). A Trp-51----Phe mutant remains pentacoordinated and exhibits only minor distal structural adjustments. The observation of a vacant sixth coordination site in this structure differs from the results of solution resonance Raman studies, which predict hexacoordinated high-spin iron [Smulevich, G., Mauro, J.M., Fishel, L. A., English, A. M., Kraut, J., & Spiro, T. G. (1988) Biochemistry 27, 5477-5485]. The coordination behavior of this W51F mutant is apparently altered in the presence of a precipitating agent, 30% 2-methyl-2,4-pentanediol. A proximal Trp-191----Phe mutant that has substantially diminished enzyme activity and altered magnetic properties [Mauro, J. M., Fishel, L. F., Hazzard, J. T., Meyer, T. E., Tollin, G., Cusanovich, M. A., & Kraut, J. (1988) Biochemistry 27, 6243-6256] accommodates the substitution by allowing the side chain of Phe-191, together with the segment of backbone to which it is attached, to move toward the heme. This relatively large (ca. 1 A) local perturbation is accompanied by numerous small adjustments resulting in a slight overall compression of the enzyme's proximal domain; however, the iron coordination sphere is essentially unchanged. This structure rules out a major alteration in protein conformation as a reason for the dramatically decreased activity of the W191F mutant. Changing proximal Asp-235 to Asn results in two significant localized structural changes. First, the heme iron moves toward the porphyrin plane, and distal water 595 now clearly resides in the iron coordination sphere at a distance of 2.0 A. The observation of hexacoordinated iron for the D235N mutant is in accord with previous resonance Raman results. Second, the indole side chain of Trp-191 has flipped over as a result of the mutation; the tryptophan N epsilon takes part in a new hydrogen bond with the backbone carbonyl oxygen of Leu-177.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding Sites↗
PubMed1990

Resonance Raman spectroscopy of cytochrome c peroxidase single crystals on a variable-temperature microscope stage.

Good quality resonance Raman (RR) spectra have been obtained for cytochrome c peroxidase single crystals (0.2 x 0.5 x 1 mm) lying on their 110 faces on a microscope stage. Crystal orientation and polarization effects are observed which differentiate the RR bands on the basis of the symmetries of the porphyrin vibrational modes. The measured depolarization ratios are accurately calibrated for isolated bands of both totally symmetric and non totally symmetric modes by using a model of D4h chromophores in an oriented gas using the crystal structure atomic coordinates. The calculations indicate that the electronic transition moments are approximately along the lines connecting the methine bridges, suggesting an electronic steering effect of the vinyl groups. Deviations are observed for bands associated with the porphyrin v10 and the vinyl C = C stretching modes, which may be due to their near-resonant interaction. The band frequencies correspond to those of a five-coordinate high-spin FeIII heme, as previously observed in solution, consistent with the X-ray structure showing the Fe atom to be out of the heme plane on the proximal side with a distal water molecule located at a nonbonded distance, 2.4 A. The temperature dependence of the RR spectrum was determined with a Joule-Thompson cryostat on crystals sealed in glass capillaries. As the temperature is lowered, the spectrum converts to one characteristic of a low-spin FeIII heme. The conversion, which is readily reversible, is quite gradual. It is detectable at -50 degrees C but is incomplete even at -190 degrees C. A temperature effect on the protein structure is proposed which permits the Fe atom to approach the heme plane and bind the distal water molecule, or the distal histidine.

Cytochrome-c Peroxidase↗
PubMed1990

Ligand binding and structural perturbations in cytochrome c peroxidase. A crystallographic study.

Crystal structures of the complexes formed between cytochrome c peroxidase and cyanide, nitric oxide, carbon monoxide, and fluoride have been determined and refined to 1.85 A. In all four complexes significant changes occur in the distal heme pocket due to movement of Arg-48, His-52, and a rearrangement of active site water molecules. In the cyanide, nitric oxide, and carbon monoxide complexes, Arg-48 moves away from the ligand while in the fluoride complex Arg-48 moves in toward the ligand to form a hydrogen bond or ion pair with the fluoride. More subtle changes occur on the proximal side of the heme. In an earlier study at lower resolution (Edwards, S. L., Kraut, J., and Poulos, T. L. (1988) Biochemistry 27, 8074-8081), we found that nitric oxide binding causes perturbations in the proximal domain involving Trp-191 which has been confirmed by the present study. Trp-191 is stacked parallel to and in contact with the proximal ligand, His-175. Nitric oxide binding results in a slight movement of Trp-191 away from His-175 and a large increase in crystallographic temperature factors indicating increased mobility of these residues on the proximal side of the heme. These proximal-side changes are unique to nitric oxide and are not related strictly to spin-state or oxidation state of the iron atom since similar changes were not observed in the cyanide (low-spin ferric), carbon monoxide (low-spin ferrous), or fluoride (high-spin ferric) complexes.

Carbon Monoxide↗
PubMed1988

Site-directed mutagenesis of yeast cytochrome c peroxidase shows histidine 181 is not required for oxidation of ferrocytochrome c.

The long-distance electron transfer observed in the complex formed between ferrocytochrome c and compound I, the peroxide-oxidized form of cytochrome c peroxidase (CCP), has been proposed to occur through the participation of His 181 of CCP and Phe 87 of yeast iso-1 cytochrome c [Poulos, T. L., & Kraut, J. (1980) J. Biol. Chem. 255, 10322-10330]. We have examined the role of His 181 of CCP in this process through characterization of a mutant CCP in which His 181 has been replaced by glycine through site-directed mutagenesis. Data from single-crystal X-ray diffraction studies, as well as the visible spectra of the mutant CCP and its 2-equiv oxidation product, compound I, show that at pH 6.0 the protein is not dramatically altered by the His 181----Gly mutation. The rate of peroxide-dependent oxidation of ferrocytochrome c by the mutant CCP is reduced only 2-fold relative to that of the parental CCP, under steady-state conditions. Transient kinetic measurements of the intracomplex electron transfer rate from ferrous cytochrome c to compound I indicate that the rate of electron transfer within the transiently formed complex at high ionic strength (mu = 114 mM, pH = 6) is also reduced by approximately 2-fold in the mutant CCP protein. The relatively minor effect of the loss of the imidazole side chain at position 181 on the kinetics of electron transfer in the CCP-cytochrome c complex precludes an obligatory participation of His 181 in electron transfer from ferrous cytochrome c to compound I.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome c Group↗
PubMed1988

Crystal structure of nitric oxide inhibited cytochrome c peroxidase.

We have collected X-ray diffraction data from a crystal of cytochrome c peroxidase (CCP) complexed with the inhibitor nitric oxide to a resolution of 2.55 A. A difference Fourier map shows density indicating the NO ligand is bound to the heme iron at the sixth coordination site in a bent configuration. Structural adjustments were determined by least-squares refinement that yielded an agreement residual of R = 0.18. The orientation of the ligand, tilting toward Arg-48, causes adjustment in the position of this nearby polar side chain. As a model for the substrate hydrogen peroxide, this geometry is consistent with the suggestion that Arg-48 serves to polarize the O-O peroxide bond to promote heterolytic cleavage of the bond [Poulos, T. L., & Kraut, J. (1980) J. Biol. Chem. 255, 8199-8205]. Strong difference density is also observed near residues 190-194, especially around the indole ring of Trp-191. The density indicates movement of the indole ring away from the proximal His-175 imidazole ring by about 0.25 A, which appears to cause perturbation of the neighboring residues. The response of Trp-191 on the proximal side of the heme to binding nitric oxide on the distal side probably results from delocalization of the electron density of the ligand. Relevant to this is the recent finding that a mutant in which Trp-191 is replaced by phenylalanine has dramatically reduced activity, less than 0.05% of the parent activity [Mauro, J. M., Fishel, L. A., Hazzard, J. T., Meyer, T. E., Tollin, G., Cusanovich, M. A., & Kraut, J. (1988) Biochemistry 27, 6243-6256].(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallization↗
PubMed1988

Crystallization and purification of the enzyme anthranilate phosphoribosyl transferase.

Anthranilate phosphoribosyl transferase from the bacterium Hafnia alvei has been crystallized. This enzyme is one of a small number that constitute the biosynthetic pathway for tryptophan. Large cubic crystals were grown at 4 degrees C by dialyzing away the glycerol from a protein solution that included ammonium sulfate, polyethylene glycol and glycerol. The crystals were much more temperature stable and resistant to X-ray deterioration than a previous, similar crystal form that had included glycerol. The crystals belong to the space group I432, a = b = c = 189 A (1 A = 0.1 nm). The ratio of the monomer molecular weight, 37,000, to the volume of the unit cell suggests that there is one homodimer per asymmetric unit. The crystals diffracted to a resolution of 3.0 A at the Stanford Synchotron Radiation Laboratory X-ray source.

Anthranilate Phosphoribosyltransferase↗
PubMed1988

Screened precession method for area detectors.

A method is presented in which the features of a Buerger-type mechanical precession camera can be simulated using an electronic area detector and a three-circle automated goniostat. The resulting display as viewed on a video monitor is very much like a conventional precession photograph. The detector is stationary which causes a distortion that is negligible for precession angles less than 10 degrees. The virtue of this new method is that a precession image may be collected very fast and the intensities of the reflections when displayed are already digitized. The usefulness of these features is presented through two familiar tasks: the determination of a new protein crystal space group and the evaluation of a heavy-atom derivative.

Anthranilate Phosphoribosyltransferase↗
PubMed1988

Where is the radical in compound I of cytochrome c peroxidase? Clues from crystallography and mutagenesis.

A difference Fourier map shows small structural perturbations on oxidation of cytochrome c peroxidase (CCP) to its semi-stable intermediate, compound I. Least-squares refinement of both CCP and compound I quantifies these perturbations and suggests that the radical site may be on the distal side of the heme, since that is where most of the small movements occur. Several engineered mutants of CCP were created in an attempt to assess the function of various side chains, among them Trp-51----Phe, Trp-191----Phe and His-181----Gly. X-ray structures of the mutant CCP's confirm that only minimal changes are caused by these substitutions. Preliminary examination of the mutants' kinetic properties show that Trp-51 is not the radical site; that Trp-191 has an important enzymic function; and that His-181 is not essential for electron transfer, but probably has some more indirect role. The locus of the radical in compound I, however, remains to be established.

Binding Sites↗
PubMed1987

Crystal structure of cytochrome c peroxidase compound I.

We have compared the 2.5-A crystal structure of yeast cytochrome c peroxidase (CCP) with that of its semistable two-equivalent oxidized intermediate, compound I, by difference Fourier and least-squares refinement methods. Both structures were observed at -15 degrees C. The difference Fourier map reveals that formation of compound I causes only small positional adjustments of a few tenths of an angstrom. The map's most pronounced feature is a pair of positive and negative peaks bracketing the heme iron position. Least-squares refinement shows that the iron atom moves about 0.2 A toward the distal side of the heme. No significant difference density is evident near the side chains of Trp-51 or Met-172, each of which has been proposed to be the site of the electron paramagnetic resonance (EPR) active radical in compound I. However, the second most prominent feature of difference density is a negative peak near the side chain of Thr-180, which, according to the results of least-squares refinement, moves by 0.15 A in the direction of Met-230. These observations, together with the results of mutagenesis experiments [Fishel, L. A., Villafranca, J. E., Mauro, J. M., & Kraut, J. (1987) Biochemistry 26, 351-360; Goodin, D. B., Mauk, A. G., & Smith, M. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 1295-1299] in which Trp-51 and Met-172 have been replaced without loss of the EPR radical signal in compound I, lead us to consider the possibility that the radical site lies within a cluster composed of the side chains of Met-230, Met-231, and Trp-191.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallization↗
PubMed1984

The crystal structure of fluoride-inhibited cytochrome c peroxidase.

The three-dimensional crystal structure of yeast cytochrome c peroxidase complexed with fluoride (F- or HF) has been determined by difference Fourier techniques and partially refined at 2.5-A resolution. Fluoride binding induces significant perturbations of the enzyme structure of the distal side of the heme. The major effect occurs at the active-site arginine residue (Arg-48) which moves about 2 A in order to optimize hydrogen-bonded interactions with the fluorine atom. A small readjustment of the distal histidine (His-52), about 0.5 A, is also seen upon fluoride binding. Additionally, a hydrogen-bonded network of 4 water molecules at the active site is reorganized. No significant movements are detectable in either the heme itself or in the proximal histidine ligand. These observations imply that movement of the Arg-48 side chain may play a key role in the enzymic mechanism of cytochrome c peroxidase. Although we cannot unequivocally determine whether fluoride is bound as HF or F-, the hydrogen-bonding pattern around the ligand points to the protonated form. Structural comparison suggests that there is a difference between the tautomeric state of the imidazole side chain of the distal histidine in cytochrome c peroxidase and of the similarly positioned distal histidine in the globins. This difference accounts for the observation that cytochrome c peroxidase preferentially binds the protonated form of ligands, whereas the globins bind the anionic form. The tautomer indicated by the peroxidase structure is the one required for acid base catalysis (Poulos, T.L., and Finzel, B. C. (1984) in Peptide and Protein Reviews (Decker, M., ed) in press).

Cytochrome-c Peroxidase↗
PubMed1980

A comparison of four personal sampling methods for the determination of mercury vapor.

Four sampling and analytical methods for mercury vapor were compared to each other in terms of precision and accuracy. The four sampling medias used were the 3M passive Mercury Vapor Monitor, the Los Alamos tandem sampling tube, the hopcalite tube, and the iodine impregnated charcoal tube. Six samples from each method were collected at nominal mercury concentrations of 0.05, 0.1, and 0.2 mg/m3. The hopcalite and 3M monitors gave comparable results at all three concentrations while the Los Alamos method gave similar results at the two highest concentrations. The iodine charcoal tube method was the only one exhibiting poor precision when tube loadings were less than 3 micrograms of mercury.

Air Pollutants↗