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S Kummer

Publications and source records attributed to S Kummer.

5 recordsLinked to original sources
PubMed2000

Fluorescence correlation spectroscopy reveals fast optical excitation-driven intramolecular dynamics of yellow fluorescent proteins.

Fast excitation-driven fluctuations in the fluorescence emission of yellow-shifted green fluorescent protein mutants T203Y and T203F, with S65G/S72A, are discovered in the 10(-6)-10(-3)-s time range, by using fluorescence correlation spectroscopy at 10(-8) M. This intensity-dependent flickering is conspicuous at high pH, with rate constants independent of pH and viscosity with a minor temperature effect. The mean flicker rate increases linearly with excitation intensity for at least three decades, but the mean dark fraction of the molecules undergoing these dynamics is independent of illumination intensity over approximately 6 x 10(2) to 5 x 10(6) W/cm(2). These results suggest that optical excitation establishes an equilibration between two molecular states of different spectroscopic properties that are coupled only via the excited state as a gateway. This reversible excitation-driven transition has a quantum efficiency of approximately 10(-3). Dynamics of external protonation, reversibly quenching the fluorescence, are also observed at low pH in the 10- to 100-microseconds time range. The independence of these two bright-dark flicker processes implies the existence of at least two separate dark states of these green fluorescent protein mutants. Time-resolved fluorescence measurements reveal a single exponential decay of the excited state population with 3.8-ns lifetime, after 500-nm excitation, that is pH independent. Our fluorescence correlation spectroscopy results are discussed in terms of recent theoretical studies that invoke isomerization of the chromophore as a nonradiative channel of the excited state relaxation.

Bacterial Proteins↗
PubMed1999

Optical methods for exploring dynamics of single copies of green fluorescent protein.

Single copies of four different phenolate ion mutants of the green fluorescent protein (GFP) exhibit a complex blinking and fluctuating behavior, a phenomenon that is hidden in measurements on large ensembles. Both total internal reflection microscopy and scanning confocal microscopy can be used to study the blinking dynamics, and autocorrelation analysis yields histograms of the correlation times for many individual molecules. While the total internal reflection method can follow several single molecules simultaneously, the confocal method offers higher time resolution at the expense of parallelism. We compare and contrast the two methods in terms of the ability to follow the complex dynamics of this system.

Green Fluorescent Proteins↗
PubMed1998

Prospective randomized trial of two different immunoadsorbers in severe systemic lupus erythematosus.

Experiences with extracorporeal therapy in systemic lupus erythematosus have been published over the last 20 years and more. In addition to plasmapheresis, specific adsorption columns have been developed to deplete pathogenic antibodies and immune complexes in the plasma of patients with SLE. We conducted a prospective randomized trial to compare the efficacy of a disposable adsorption column, which contained a specific ligand, phenylalanine (IMPH-350|Pt, Diamed, Köln, Germany) with a regenerable Ig-adsorbing column containing sheep anti-human antibodies (Ig-Therasorb|Pt, Therasorb, München, Germany). Twenty SLE patients inadequately controlled with corticosteroids, anti-malarials, azathioprine or cyclosporine A, had strong evidence of disease in general, or an organ related SLAM score. They were randomized to receive either a perfusion of IMPH-350, or Ig-Therasorb, immunoadsorbed with 2.5 ml of plasma, three times each. The treatment regime was repeated after 4 weeks when the response was limited or non-existent. Response was defined as a reduction in the SLAM score of at least 30%. SLAM scores in the IMPH group decreased from 14.3+/-5.6 to 9.2+/-6.2 after 1 month and to 9.4+/-3.9 after 6 months; corresponding scores in the Ig-Therasorb group were 18.3+/-5. 5 to 11.2+/-7.6, decreasing to 9.2+/-2.9. After 1 month, 8/10 patients in both groups showed a response; after 6 months, 5/10 patients in the IMPH-350 group and 8/10 in the Ig-Therasorb group fulfilled the response criteria. Reduction of dsDNA antibodies directly after treatment was 50.8+/-6.6% in the IMPH-350 group and 61.0+/-8.0% in the IgTherasorb group. Results indicate that immunoadsorption is an additional option in the treatment of severe SLE. Choice of type of immunoadsorber and immunosuppressive treatment has to take into account the severity and chronicity of common disease activity and organ involvement, as well as economic aspects.

Adult↗