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K Bernhardt

Publications and source records attributed to K Bernhardt.

7 recordsLinked to original sources
PubMed2001

Evidence for protein dielectric relaxations in reaction centers associated with the primary charge separation detected from Rhodospirillum rubrum chromatophores by combined photovoltage and absorption measurements in the 1-15 ns time range.

Fast photovoltage measurements in Rhodospirillum rubrum chromatophores in the nanosecond time range, escorted by time-resolved absorption measurements, are described. Under reducing conditions, the photovoltage decayed significantly faster than the spectroscopically detected charge recombination of the radical pair P(+)H(A)(-). This indicates the occurrence of considerable dielectric relaxations. Our data and data from the literature were analyzed by means of a reaction scheme consisting of three states, namely, A, P, and P(+)H(A)(-). A time-dependent DeltaG(t) was introduced by assuming a time-dependent rate constant of the back-reaction, k(-1)(t). With the exception of the latter rate constant, all other parameters of the model are reliably known within narrow limits. This allowed us to distinguish between the three cases assumed for DeltaG degrees (t): (1)DeltaG degrees (t) = constant; (2)DeltaG degrees (t) as published by Peloquin et al. [Peloquin, J. M., Williams, J. C., Lin, X. M., Alden, R. G., Taguchi, A. K. W., Allen, J. P., and Woodbury, N. W. (1994) Biochemistry 33, 8089-8100]; and a (3)DeltaG degrees (t) that fits the present data. The assumption that (1)DeltaG degrees (t) = constant is incompatible with our photovoltage data, and (2)DeltaG degrees (t) is incompatible with the constraint that the ratio of fluorescence yields in the closed and open state is F(m)/F(o) approximately 2. We specify a (3)DeltaG degrees (t) that should be valid for photosynthetic reaction centers in vivo. Furthermore, the overall kinetics of the electric relaxation, e(t), in response to the primary charge separation were determined.

Bacterial Chromatophores↗
PubMed2000

Escape probability and trapping mechanism in purple bacteria: revisited.

Despite intensive research for decades, the trapping mechanism in the core complex of purple bacteria is still under discussion. In this article, it is attempted to derive a conceptionally simple model that is consistent with all basic experimental observations and that allows definite conclusions on the trapping mechanism. Some experimental data reported in the literature are conflicting or incomplete. Therefore we repeated two already published experiments like the time-resolved fluorescence decay in LH1-only purple bacteria Rhodospirillum rubrum and Rhodopseudomonas viridis chromatophores with open and closed (Q(A)(-)) reaction centers. Furthermore, we measured fluorescence excitation spectra for both species under the two redox-conditions. These data, all measured at room temperature, were analyzed by a target analysis based on a three-state model (antenna, primary donor, and radical pair). All states were allowed to react reversibly and their decay channels were taken into consideration. This leads to seven rate constants to be determined. It turns out that a unique set of numerical values of these rate constants can be found, when further experimental constraints are met simultaneously, i.e. the ratio of the fluorescence yields in the open and closed (Q(A)(-)) states F(m)/F(o) approximately 2 and the P(+)H(-)-recombination kinetics of 3-6 ns. The model allows to define and to quantify escape probabilities and the transfer equilibrium. We conclude that trapping in LH1-only purple bacteria is largely transfer-to-the-trap-limited. Furthermore, the model predicts properties of the reaction center (RC) in its native LH1-environment. Within the framework of our model, the predicted P(+)H(-)-recombination kinetics are nearly indistinguishable for a hypothetically isolated RC and an antenna-RC complex, which is in contrast to published experimental data for physically isolated RCs. Therefore RC preparations may display modified kinetic properties.

Bacterial Chromatophores↗
PubMed1999

Theories for kinetics and yields of fluorescence and photochemistry: how, if at all, can different models of antenna organization be distinguished experimentally?

The models most commonly used to describe the antenna organization of the photosynthetic membrane are the connected units model and the domain model. The theoretical descriptions of the exciton dynamics according to these models are reviewed with emphasis on a common nomenclature. Based on this nomenclature we compare for the two models the kinetics and yields of photochemistry and fluorescence under non-annihilation and annihilation conditions both under continuous light and under flash excitation. The general case is considered, that all initially open reaction centers become gradually closed and that exciton transfer between photosynthetic units (PSUs) is possible. Then, calculated kinetics and yields depend on the model assumptions made to account for the exciton transfer between PSUs. Here we extend the connected units model to flash excitation including exciton-exciton annihilation, and present a new simple mathematical formalism of the domain model under continuous light and flash excitation without annihilation. Product and fluorescence yields predicted by the connected units model for different degrees of connectivity are compared with those predicted by the domain model using the same sets of rate constants. From these calculations we conclude that it is hardly possible to distinguish experimentally between different models by any current method. If at all, classical fluorescence induction measurements are more suited for assessing the excitonic connectivity between PSUs than ps experiments.

Journal Article↗
PubMed1997

[Flow cytometry for extensive thoracic diagnosis].

Immunophenotyping of cells by flow cytometry has become a routine test to diagnose pulmonary and mediastinal diseases. Peripheral blood, extravascular fluids, bronchoalveolar lavage (BAL) and suspension of single cells obtained by fine-needle aspiration can be used. Peripheral blood (MOAb for immunophenotyping of lymphocytes: CD14, CD45, CD3, CD19, CD4, CD8, CD16/56, HLA DR, CD38, CD25) is the material of choice for detection and monitoring of immunodeficiences. BAL (MOAb for immunophenotyping of lymphocytes: CD14, CD45, CD3, CD19, CD4, CD8, CD16/56, HLA DR) is used mainly for differential diagnosis of extrinsic allergic alveolitis (low CD4/CD8 ratio) and sarcoidosis (high CD4/CD8 ratio). The enumeration of alveolar macrophage subsets is an important tool to establish diagnosis of histiocytosis X (CD1a > 3%). Extravascular fluids, suspension of single cells and BAL are preferred materials for detection and classification of non-Hodgkin lymphomas (MOAb for immunophenotyping of lymphocytes: CD14, CD45, CD3, CD19, CD4, CD8, CD16/56, HLA DR, CD38, CD25, CD23, CD5, CDl1c, CD30, light chain immunoglobulins).

Diagnosis, Differential↗
PubMed1995

[Idiopathic CD4+ T-lymphocytopenia in 2 patients without indications for HIV infection].

We report on two patients with idiopathic CD4+ T cell depletion. A 26 year-old woman presented to us with acute respiratory failure requiring mechanical ventilation. Despite combined antibiotic therapy parenterally the opacities increased in the chest X-ray. An open lung biopsy was performed and led to the histological diagnosis of bronchiolitis obliterans organizing pneumonia (BOOP). Respiratory function was improved impressively by high dose parenteral cortisone administration. This patient showed a general lymphocytopenia with severe CD4+ T cell depletion (60(37%)/mm3 blood). The CT4+ T cell concentration increased during a follow up period of 14 months, but did not reach normal values. The second patient was a 33 year-old homosexual. He was admitted with a mucocutaneous fungal infection which was successfully treated by antifungal drugs. This patient demonstrated a transient CD4+ T cell depletion (350(32%)/mm3 blood). In both patients HIV type 1 and 2 infections were excluded by antibody- and p 24-antigen testing, polymerase chain reaction and virus culture. CONCLUSION. Idiopathic CD4+ T lymphocytopenia differs from HIV infection in immunological profile, in the tendency to reversal of the CD4+ T cell depletion over time and in its better prognosis. It is unclear if this is a new syndrome and whether a transmissible agent, or possibly a genetically-determined reaction to noxious agents is responsible.

Adult↗
PubMed1975

Implications of genetic variation in mouse brain structure for electrode placement by stereotaxic surgery.

The spatial locations of several forebrain and midbrain fibre tracts have been compared across seven commonly used inbred, hybrid and outbred mouse strains using a series of electrolytic lesions of known positions with respect to a stereotaxic instrument. Highly significant genetic variation was found in the position of lambda, bregma and several major fibre tracts with respect to interaural zero; in the locations of fibre tracts with respect to bregma; and in the location of fibre tracts with respect to each other. It was demonstrated that stereotaxic coordinates of a structure for one strain could not be used for other strains. Errors resulting from improper alignment of the head in the instrument and histological artifact were also determined. These errors showed no significant group differences, but they revealed that within-group variation was substantially affected by such imperfections.

Animals↗