Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Freitag
modes. As a microscopic example a model of ion-channels with openclosing
kinetics embedded in a biomembrane is presented. This model
leads to generic amplitude equations occuring in systems with conserved
order parameter and are furthermore studied in the general case of a
simple reaction-diffusion system.
AKB 50.115 Fr 10:30 B
Hopf-bifurcations in systems with conserved quantities —
•Markus Hilt and Walter Zimmermann — Theoretische Physik,
Universität des Saarlandes, 66041 Saarbrücken
A cubic Ginzburg–Landau equation is presented, which describes for
the first time the universal properties of a Hopf-bifurcation in a system
with conserved quantities. This bifurcation occurs for instance in a model
describing the dynamics of two interacting ion-channels in a membrane.
It is a universal feature of this bifurcation that all nonlinear traveling
wave solutions are linear unstable in general, besides the smallest possible
wavenumber in a finite system with periodic boundary conditions.
Spatio-temporal chaos occurs either due to boundary effects or due to
an extension of the destabilizing wavenumber band. This scenario is different
from other cases, where spatio-temporal chaos often occurs, as for
instance for one of the most studied nonlinear equations in physics, the
Ginzburg–Landau equation for unconserved systems (see e.g. I. Aranson
and L. Kramer, Rev. Mod. Phys. 74, 99 (2002)).
AKB 50.116 Fr 10:30 B
Fluorescence Excitation Spectroscopy on Single Light-
Harvesting Complexes of Higher Plants — •Carsten Tietz 1 ,
Sebastian Schuler 1 , Fedor Jelezko 1 , Heiko Lokstein 2 ,
and Jörg Wrachtrup 1 — 1 3. Physikalisches Institut, Universität
Stuttgart, 70550 Stuttgart, Germany — 2 Institut für Pflanzenphysiologie,
Humboldt-Universität Berlin, 10099 Berlin, Germany
Photosynthesis of higher plants and green algae is the most important
metabolic process on earth. The absorption of light in higher plants is
carried out by pigment-protein complexes. Besides the well known major
Light-Harvesting Complex II (LHCII) that exists in a trimeric form
there are several minor chlorophyll (Chl) a and b binding complexes to
be found in Photosystem 2.
Single molecule spectroscopy has been used to investigate the photophysics
of the minor plant antenna CP29 in its native monomeric form.
This complex binds 8 chlorophylls of which 2 are supposed to be Chl
b and 6 Chl a. Although the structure is not known, sequence analysis
showed a strong resemblance between LHCII monomers and CP29.
Therefore it was possible to construct a structural model of CP29 on the
basis of LHCII.
With combined excitation and emission spectra of single CP29 complexes
at low temperatures (2 K), we can gather information about the
energy levels of the bound Chl molecules, the relative orientation of their
transition dipole moments and the energy transfer rate. Here we report
on the first fluorescence excitation spectra of single CP29 complexes.
AKB 50.117 Fr 10:30 B
Cell Adhesion onto Highly Curved Particle Surfaces - One-
Step Immobilization of Cell Membranes — •Motomu Tanaka
und Stefan Kaufmann — Biophysics Lab, Tech. Univ. Munich
We report single-step, orientation selective immobilization of human
erythrocyte membranes on bare silica beads with different topographies:
1) solid (nonporous) silica beads with a diameter of 3 microns and 2) porous
silica beads with a diameter of 5 microns. Erythrocyte membranes
were immobilized onto beads simply by incubation, without sonication or
osmotic lysis. Membrane orientation before and after the immobilization
was identified with a first monoclonal antibody and a second fluorescent
polyclonal antibody. Adherent erythrocytes on the beads all ruptured,
inverted the asymmetric orientation of the membrane, and selectively
exposed their cytoplasmic domain. The surface topography did not influence
orientation or the amount of immobilized membranes. On the other
hand, the fact that no adsorption or rupture of erythrocytes could be
observed on planar quartz substrates suggests a significant influence of
contact curvatures on the adhesion free energy.
AKB 50.118 Fr 10:30 B
Analysis of Spatiotemporal Data Sets in Dictyostelium —
•Christiane Hilgardt 1 , Marc-Thorsten Hütt 2 , and Stefan C.
Müller 1 — 1 Otto-von-Guericke Universität Magdeburg, Institut für
Experimentelle Physik, Abteilung Biophysik, Universitätsplatz 2, 39106
Magdeburg — 2 Technische Universität Darmstadt, Institut für Botanik,
Arbeitsgruppe Theoretische Biologie und Bioinformatik, Schnittspahnstraße
3, 64287 Darmstadt
We investigate reaction-diffusion waves in the slime mould Dictyostelium
with spatiotemporal analysis filters, [1, 2, 3]. Our hypothesis
is that the spatial distribution of cell properties determines the architecture
of structures in later morphogenetic stages, e.g. aggregation
streams. Our investigations address the constructive role of variability
in biological structure formation. To this goal we visualize local inhomogeneities
in fluctuations, which allow to distinguish between fast and
directed dynamics. We correlate extremal behavior with later structures.
In particular, we focus on the borders between the different states of
an excitable medium (excitable, excited and refractory) to evaluate biological
variability as the ”roughness” of these border lines. First results
support our hypothesis. The spatial distribution of our observable shows
an elevated correlation with the position of later aggregation streams.
Furthermore, methods of information theory and estimation theory from
sequence analysis are developed and applied to the spatiotemporal data
sets. [1] Müller S. C. et al. (1998) Biophys. Chem. 72: 37-47. [2] Hütt
M.-Th., Neff R. (2001) Physica A 289: 498-516. [3] Hütt M.-Th. et al.
(2002) Phys. Rev. E. 66: 26117.
AKB 50.119 Fr 10:30 B
Functional Micro-Domains of Glycolipids with Partially Fluorinated
Membrane Anchors - Impact on Cell Adhesion —
•Motomu Tanaka 1 , Matthias Schneider 1 , Laurent Limozin 1 ,
Doris Heinrich 1 , Gabriele Schumacher 2 , Gerd Bendas 2 , Ulrich
Rothe 3 , Christian Gege 4 , and Richard Schmidt 4 — 1 Dept.
Physics E22, Tech. Univ. Munich — 2 Dept. Pharmacy, Univ. Bonn —
3 Dept. Physiol. Chem., Univ. Halle — 4 Dept. Chem., Univ. Konstanz
Functional micro-domains of glycolipids were designed by mixing neoglycolipids
with partially fluorinated (F-alkyl) chains and matrix lipids
with alkyl chains. Fluorescence images of the mixed lipid monolayers
at air/water interface demonstrated that it is possible to control both
size and distribution of the micro-domains according to the strong demixing
of alkyl and F-alkyl membrane anchors, while the correlation
between carbohydrate head groups seemed to play rather minor roles.
These micro-domains in monolayers could be transferred onto hydrophobized
substrates, and subjected to dynamic flow chamber experiments.
The results obtained here clearly indicated that the dynamic adhesion of
Chinese hamster ovarial cells expressing E-selectin (CHO-E cells) onto
the lipid monolayer containing micro-domains of sialyl LewisX (sLeX)
can be both enhanced and reduced by controlled de-mixing of ligands
and matrices. Moreover, the same clusters of sLeX could also be formed
in giant lipid vesicles, which can be used as a model cell that locally
expresses bio-specific functions.
AKB 50.120 Fr 10:30 B
Functional Micro-Domains of Glycolipids with Partially Fluorinated
Membrane Anchors - Impact on Cell Adhesion —
•Motomu Tanaka 1 , Matthias Schneider 1 , Laurent Limozin 1 ,
Doris Heinrich 1 , Gabriele Schumacher 2 , Gerd Bendas 2 , Ulrich
Rothe 3 , Christian Gege 4 , and Richard Schmidt 4 — 1 Dept.
Physics E22, Tech. Univ. Munich — 2 Dept. Pharmacy, Univ. Bonn —
3 Dept. Physiol. Chem., Univ. Halle — 4 Dept. Chem., Univ. Konstanz
Functional micro-domains of glycolipids were designed by mixing neoglycolipids
with partially fluorinated (F-alkyl) chains and matrix lipids
with alkyl chains. Fluorescence images of the mixed lipid monolayers
at air/water interface demonstrated that it is possible to control both
size and distribution of the micro-domains according to the strong demixing
of alkyl and F-alkyl membrane anchors, while the correlation
between carbohydrate head groups seemed to play rather minor roles.
These micro-domains in monolayers could be transferred onto hydrophobized
substrates, and subjected to dynamic flow chamber experiments.
The results obtained here clearly indicated that the dynamic adhesion of
Chinese hamster ovarial cells expressing E-selectin (CHO-E cells) onto
the lipid monolayer containing micro-domains of sialyl LewisX (sLeX)
can be both enhanced and reduced by controlled de-mixing of ligands
and matrices. Moreover, the same clusters of sLeX could also be formed
in giant lipid vesicles, which can be used as a model cell that locally