| 1. |
- Bergqvist, Björn, 1965, et al.
(author)
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Effect of microwave radiation on permeability of liposomes. Evidence against non-thermal leakage
- 1994
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In: Biochimica et Biophysica Acta - General Subjects. - : Elsevier BV. - 1872-8006 .- 0304-4165. ; 1201:1, s. 51-54
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Journal article (peer-reviewed)abstract
- The effect of 2.45 GHz microwave radiation on the permeability of unilamellar phosphatidylcholine liposomes has been studied. Leakage of 5(6)-calboxyfluorescein from the liposomes was measured using spectrofluorimetry after exposure to either microwaves or thermal heating for 5-20 min intervals. The exposure temperature, 37.6 +/- 0.5 degrees C, was well above the phase transition temperature of the lipid membrane. The microwave exposure did not result in any non-thermal increase in permeability above that produced by thermal heating. This study refutes the results reported by Saalman et al. [1] in which an increased liposome permeability due to microwave exposure was reported. The refined analysis in the present study shows that this increased liposome permeability was not a non-thermal microwave effect.
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| 2. |
- Breccia, Javier D, et al.
(author)
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The role of poly(ethyleneimine) in stabilization against metal-catalyzed oxidation of proteins: a case study with lactate dehydrogenase.
- 2002
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In: Biochimica et Biophysica Acta. General Subjects. - 0304-4165. ; 1570:3, s. 165-173
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Journal article (peer-reviewed)abstract
- The protection provided by poly(ethyleneimine) (PEI) to muscle lactate dehydrogenase (LDH) in metal-catalyzed oxidation (MCO) systems (CuSO(4) or FeCl(2) combined with H(2)O(2)) was studied, and comparisons were made with the chelators EDTA and desferal, respectively. The analytical chelating capacity of PEI was estimated to be around 1 mol Cu(2+)/10 mol ethyleneimine for all molecular weights of the polymer. The effect of [PEI monomer]/[metal ion] molar ratio on the oxidatively induced aggregation of LDH exhibited a similar trend as that of the other chelators; aggregation was enhanced at lower ratios and subsequently decreased until it was undetectable with increasing ratio. In contrast, the LDH activity showed a monotonic increase with increasing concentrations of the chelator. Total protection to the enzyme by PEI was provided at concentrations lower than that needed for full chelation of the copper ions, i.e. at [PEI monomer]/[Cu(2+)] ratio above 9 in case of PEI 2000, and above 7 for PEI 25000 and 2.6 x 10(6), respectively. The polymer also provided protection against oxidation in an iron-based MCO system. Hydroxyl radical formation during the MCO reaction was inhibited in the presence of PEI. The polymer of higher molecular weights also exhibited a stronger free radical scavenging effect.
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| 3. |
- Johansson, Hans-Olof, et al.
(author)
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Effects of ions on partitioning of serum albumin and lysozyme in aqueous two-phase systems containing ethylene oxide/propylene oxide co-polymers
- 1996
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In: Biochimica et Biophysica Acta. General Subjects. - : Elsevier BV. - 0304-4165. ; 1290:3, s. 289-298
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Journal article (peer-reviewed)abstract
- Aqueous two-phase systems composed of ethylene oxide/propylene oxide random co-polymers, EO30/PO70 or Ucon (EO50/PO50), in the top phase and dextran T500 in the bottom phase, have been studied. The cloud point diagram for EO30/PO70 in water solution was determined. EO30/PO70 has a cloud point of 32oC at a concentration of 10% (w/w). The phase diagram for the system EO30/PO70-dextran T500-water was determined. Salt effects have been studied on the partitioning of two model proteins, bovine serum albumin and hen egg white lysozyme, in EO30/PO70-dextran and Ucon-dextran systems. Ions with different hydrophobicity, i.e., with different position in the Hofmeister or lyotropic series, were investigated with reference to their effect on protein partition. The counterion hydrophobicity was shown to have a strong influence on the partitioning of BSA and lysozyme. Most extreme partitioning was obtained with hydrophobic (chaotropic) ions like ClO-4 and I-. A comparison of protein partitioning between PEG-dextran and EO30/PO70-dextran has been done. A more extreme protein partitioning was obtained in the EO30/PO70-dextran containing system. Temperature-induced phase separation was studied with EO30/PO70 at 45oC. Both BSA and lysozyme were completely partitioned to the water phase formed above the cloud point of EO30/PO70. Model calculations, based on Flory-Huggins theory of polymer solutions, have been done which could reproduce the salt effect on the protein partitioning in aqueous-two phase system.
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| 4. |
- Johansson, Hans-Olof, et al.
(author)
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Temperature-induced phase partitioning of peptides in water solutions of ethylene oxide and propylene oxide random copolymers
- 1997
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In: Biochimica et Biophysica Acta. General Subjects. - 0304-4165. ; 1335:3, s. 315-325
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Journal article (peer-reviewed)abstract
- A thermoseparating random copolymer (Ucon 50-HB-5100) composed of (50%) ethylene oxide and (50%) propylene oxide has been used to form an aqueous two-phase system by heating the polymer-water solution above the cloud point of the copolymer. In the formed two-phase system a water rich top phase is in equilibrium with an aqueous polymer rich bottom phase. The partitioning of amino acids and peptides in this aqueous two-phase system has been studied. Hydrophobic peptides (containing aromatic amino acids) were strongly partitioned to the polymer rich phase, while hydrophilic peptides were enriched in the water rich phase. The effect of temperature on the partitioning was investigated and a decreased partitioning to the polymer rich phase was obtained upon temperature increase. The effect of two salts (NaClO4 and Na2SO4) on the partitioning of a positively charged polypeptide, poly(Lys, Trp), was very strong. With NaClO4 the polypeptide was quantitatively partitioned to the polymer rich phase while with Na2SO4 the polypeptide was partitioned to the water rich phase. Model calculations based on a modified Flory-Huggins theory have been performed to better understand the experimental behavior.
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| 5. |
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| 6. |
- Lohmander, Stefan, et al.
(author)
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Chemical and metabolic heterogeneity of chondroitin sulfate and keratan sulfate in guinea pig cartilage and nucleus pulposus
- 1973
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In: Biochimica et Biophysica Acta. General Subjects. - : Elsevier BV. - 0304-4165. ; 304:2, s. 430-448
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Journal article (peer-reviewed)abstract
- Chondroitin sulfate and keratan sulfate in guinea pig costal cartilage, nasal septum cartilage and nucleus pulposus were separated and fractionated by chromatography on CPC-cellulose, ECTEOLA-cellulose and Sephadex G-200 columns. Characterization of the chondroitin sulfates included determination of molecular weight and of the number, and position, of sulfate groups of the disaccharide units. Distinct chemical differences were found between the total fractions of chondroitin sulfate from the three tissues. Within the total fractions a marked heterogeneity was also apparent. The turnover of the two glycosaminoglycans was studied by using radioactive sulfate as precursor. The guinea pigs were killed at eight intervals, ranging from 30 min to 40 days after injection of the isotope. Total fractions of chondroitin sulfate from rib, nasal septum and nucleus pulposus showed half-lives of about 80, 40 and 30 days, respectively. In addition, the existence of a second metabolic component with a faster turnover (half-life about 3 days) was indicated in chondroitin sulfate from all three tissues. Similarly, keratan sulfate from the rib contained a 'slow' component with a half-life of about 90 days and a 'fast' component with a half-life of 4 days. For keratan sulfate from nucleus pulposus only a single component was demonstrable; it had a half-life of about 30 days. Within the total fractions of both chondroitin sulfate and keratan sulfate from the three tissues studied, a considerable degree of metabolic heterogeneity was apparent between, and within, subfractions of differing molecular weight.
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| 7. |
- Lohmander, Stefan
(author)
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Ion exchange chromatography of glucosamine and galactosamine in microgram amounts with quantitative determination and specific radioactivity assay
- 1972
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In: Biochimica et Biophysica Acta. General Subjects. - : Elsevier BV. - 0304-4165. ; 264:3, s. 411-417
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Journal article (peer-reviewed)abstract
- A rapid method for the separation and quantitative determination, including radioassay, of glucosamine and galactosamine in microgram amounts is described. It is based upon the use of a column of Aminex A-5 ion exchange resin eluted with a phosphate buffer at pH 7.00 and 60 °C. From each fraction half the volume is used for a scaled down Elson-Morgan procedure and other half for liquid scintillation counting. Amounts of about 0.01-1 μmole of hexosamine may be separated and determined.
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| 8. |
- Lohmander, Stefan, et al.
(author)
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Proteoglycans of mineralizing rib and epiphyseal cartilage
- 1975
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In: Biochimica et Biophysica Acta. General Subjects. - : Elsevier BV. - 0304-4165. ; 404:1, s. 93-109
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Journal article (peer-reviewed)abstract
- Rib cartilage from growing guinea pigs and epiphyseal cartilage from Beagle puppie were separated into three fractions, representing non-mineralized, low mineralized, and high mineralized, tissue, by centrifuging finely ground material in acetone/bromoform density gradients. Following extraction under dissociative conditions, the proteoglycans were fractionated by density gradient ultracentrifugation under associative and dissociative conditions. With the onset of mineralization, the cartilage lost approximately half its content of proteoglycans. The proteoglycans remaining in the calcified cartilage differed in composition and in size from those of nonmineralized tissue. With the increased mineral content of the tissues the ratios of protein to polysaccharide, of chondroitin sulfate to keratan sulfate, and of 4-sulfated to 6-sulfated chondroitin sulfate increased in the proteoglycan fraction. Furthermore, gel chromatograms indicated decreased proportions of very high molecular weight proteoglycans, in mineralized tissue.
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| 9. |
- Pettersson, Gösta
(author)
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Error associated with experimental flux control coefficient determinations in the Calvin cycle
- 1996
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In: Biochimica et Biophysica Acta. General Subjects. - 0304-4165. ; 1289:2, s. 169-174
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Journal article (peer-reviewed)abstract
- Model studies of photosynthetic carbohydrate formation in the chloroplast of C3 plants have been performed to examine the expected response of the steady-state reaction flux to finite changes in concentration or activity of individual enzymes in a central metabolic network. The results indicate that flux control coefficients in this system cannot be reliably estimated experimentally even for the two enzymes that do exert predominant control under the examined conditions. Reduction of the mathematical error of the estimates to a satisfactorily low level requires such small enzyme concentration changes that presently available assay methods do not allow for a determination of the corresponding flux changes with satisfactory precision.It is concluded from these observations and general methodological considerations that experimental flux control coefficient estimates cannot be trusted unless evidence is presented to show that the mathematical error associated with their determination is of insignificant magnitude.
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| 10. |
- Shipovskov, S, et al.
(author)
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Stabilisation of tyrosinase by reversed micelles for bioelectrocatalysis in dry organic media
- 2003
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In: Biochimica et Biophysica Acta. General Subjects. - 0304-4165. ; 1620:1-3, s. 119-124
-
Journal article (peer-reviewed)abstract
- The enzymatic and bioelectrocatalytic activity of tyrosinase from mushrooms was studied in a system of reversed micelles formed by Aerosol OT (AOT) in hexane. The optimal catechol oxidising activity of tyrosinase incorporated in reversed micelles was found at a hydration degree of w(0) = 25. The catalytic activity was comparable with tyrosinase activity in aqueous media. When immobilized at an Au electrode, either directly or in reversed micelles, tyrosinase exhibited a similar efficiency of the bioelectrocatalytic reduction of O-2 mediated by catechol; however, a rapid decrease in the activity correlated with the destruction of reversed micelles and/or the removal of tyrosinase from the electrode surface. The system containing tyrosinase in reversed micelles with caoutchouk, spread on the surface of the An electrode and successively covered with a Nafion(R) membrane layer, was found to result in stable tyrosinase-modified electrodes, which were resistant to inactivation in dry acetonitrile. The proposed technique offers possibilities for further development of highly active and stable surfactant/enzyme-modified electrodes for measurements carried out in organic solvents. (C) 2002 Elsevier Science B.V. All rights reserved.
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