PubMed Health⌕ Search

Biomedical subjects

O Hansson

Publications and source records attributed to O Hansson.

At least 19 recordsLinked to original sources
PubMed1992

A membrane-bound monoheme cytochrome c551 of a novel type is the immediate electron donor to P840 of the Chlorobium vibrioforme photosynthetic reaction center complex.

A photosynthetic reaction center complex has been isolated from the green sulfur bacterium Chlorobium vibrioforme. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals polypeptides with apparent molecular masses of 80, 40, 18, 15, 9, and 6 kDa. Only the 18-kDa polypeptide is stained with 3,3',5,5'-tetramethylbenzidine, a heme-specific reagent. Oxidized minus reduced difference spectra show the presence of approximately one heme/P840 and the presence of a cytochrome c551. Flash photolysis of P840 was followed by rereduction of P840+ and oxidation of cytochrome c551, both with a biphasic kinetic with t1/2 values of 7 and 50 microseconds. Using oligonucleotide probes derived from an N-terminal amino acid sequence of the 18-kDa polypeptide, a genomic clone was isolated. The sequence of the gene, which we designate cycA, predicts a single heme binding site (Cys-Asn-Lys-Cys-His). The 621-base pair open reading frame encodes an apoprotein of 22,858 Da with three predicted membrane-spanning alpha-helices. No extensive sequence similarity is found to other cytochromes. Northern blotting indicates that the cycA gene is transcribed as a monocistronic mRNA. Southern blotting shows the presence of only one cycA gene in the C. vibrioforme and Chlorobium tepidum genomes. The unique membrane-bound monoheme cytochrome c551 of C. vibriforme is assigned to a new class of c-type cytochromes. The implications for the current view of evolution of photosynthetic reaction center complexes are discussed.

Amino Acid Sequence↗
PubMed1992

Reactivity of cytochromes c and f with mutant forms of spinach plastocyanin.

The reduction of plastocyanin by cytochromes c and f has been investigated with mutants of spinach plastocyanin in which individual, highly conserved surface residues have been modified. These include Leu-12 and Phe-35 in the 'northern' hydrophobic patch and Tyr-83 and Asp-42 in the 'eastern' acidic patch. The differences observed all involved binding rather than the intrinsic rates of electron transfer. The Glu-12 and Ala-12 mutants showed small but significant decreases in binding constant with cytochrome c, even though the cytochrome is not expected to make contact with the northern face of plastocyanin. These results, and small changes in the EPR parameters, suggested that these mutations cause small conformational changes in surface residues on the eastern face of plastocyanin, transmitted through the copper centre. In the case of cytochrome f, the Glu-12 and Ala-12 mutants also bound less strongly, but Leu12Asn showed a marked increase in binding constant, suggesting that cytochrome f can hydrogen bond directly to Asn-12 in the reaction complex. A surprising result was that the kinetics of reduction of Asp42Asn were not significantly different from wild type, despite the loss of a negative charge.

Amino Acid Sequence↗
PubMed1991

Flash-photolysis studies of the electron transfer from genetically modified spinach plastocyanin to photosystem I.

Plastocyanin (Pc) has been modified by site-directed mutagenesis at two separate electron-transfer (ET) sites: Leu-12-Glu at a hydrophobic patch, and Tyr-83-His at an acidic patch. The reduction potential at pH 7.5 is decreased by 26 mV in Pc(Leu-12-Glu) and increased by 35 mV in Pc(Tyr-83-His). The latter mutant shows a 2-fold slower intracomplex ET to photosystem I (PSI) as expected from the decreased driving force. The affinity for PSI is unaffected for this mutant but is drastically decreased for Pc(Leu-12-Glu). It is concluded that the hydrophobic patch is more important for the ET to PSI.

Electron Spin Resonance Spectroscopy↗
PubMed1990

Strength of bond with Comspan Opaque to three silicoated alloys and titanium.

In Sweden high-gold alloys or cobalt-chromium alloys are used for resin-bonded prostheses. The bond strength between a resin cement and different sandblasted or silicoated metals were measured before and after thermocycling; in connection with this some rapid thermocycling methods were studied. The effect of different storage times and different protection coatings on bond strength were tested. Finally, the influence of rubbing and contamination with saliva on bond strength were investigated. Silicoating increased the bond strength significantly. The highest bond strengths were these of silicoated Wirobond and titanium, unsusceptible to thermal stress; the bond strengths of the sandblasted metals were the weakest, and sensitive to thermocycling as well. The influence on bond strength for silicoated gold alloys, protected with an unpolymerized composite resin coating, stored in sealed plastic bags up to 7 days, was negligible. Rubbing and contamination with saliva did not influence bond strength. Preferably, silicoated Wirobond and titanium should be used for resin-bonded prostheses, but gold alloys may still be adequate for clinical use. The experimental method described for storing, sealing, and cleaning the silicoated metal surfaces in this article can be recommended for laboratory and clinical use.

Composite Resins↗
PubMed1988

Impressions for prosthodontic restorations reproducing narrow spaces and severe undercuts.

Distortion of an impression material may occur in special clinical situations in which the material's elastic limit is exceeded. Impressions were made of a master model designed to test such situations. Three different hydrocolloids and an addition silicone were used in the experiment. An extended setting time had to be used for one material, to prevent it from tearing. When this extended time was used, this material was the dimensionally most accurate material in the test. All materials were accurate in reproducing normally positioned abutments, while some of the impressions failed to reproduce adjacent abutments with particularly narrow interspaces; narrow passages may therefore require further tooth preparation. In the most severely undercut area differences existed among the materials, and sometimes tears occurred. When the papilla is missing, the undercut area should be blocked out to prevent plastic deformation of the impression material, causing inaccurate restorations.

Agar↗
PubMed1985

Casting accuracy of a nickel and beryllium-free cobalt-chromium alloy for crown and bridge prostheses and resin-bonded bridges.

In the 1970's economic factors dictated the development of alternatives to gold alloys in dentistry in the USA and in Europe. A similar development has not occurred in Sweden because of different laws. Alloys that contain nickel and beryllium present a health hazard and are therefore of little interest to the Swedish market. A review of the literature shows that castings of base-metal alloys are less accurate than castings of conventional gold alloys and of low gold alloys. However, in long-span-bridges and in thin resin-bonded cast restorations, their physical and mechanical properties are superior to those of the gold alloys. In this study the casting accuracy of a nickel- and beryllium-free cobalt-chromium alloy, Neobond II Special, is investigated. Neobond II Special was found to be less accurate than Sjödings C-guld. The marginal discrepancies of the castings were small, however, when the castings were oversized. It also proved to be technique sensitive to conventional dental laboratory procedures. Thus, it seems difficult to get castings with an acceptable retention as well as small marginal discrepancies when using the base-metal alloy.

Chemical Phenomena↗