VEMH - Virtual Euro-Mediterranean Hospital for Global Healthcare.

The Virtual Euro-Mediterranean Hospital (VEMH) aims to facilitate the interconnection of various medical services through real integration. VEMH will provide an integrated satellite-terrestrial platform and realize telemedical services such as e-learning, real-time telemedicine and medical assistance and offer individual grants to young medical doctors. The methodologies of the VEMH are medical-need-oriented instead of technology-oriented. VEMH will provide for medical professionals in the whole Euro-Mediterranean area access to the required quality of medical service. For the successful deployment of the services of the VEMH GRID technologies have to be implemented especially for evidence-based medicine. A Metagrid Service Engine implements an additional software layer between proprietary GRID engines and the different applications. The use of mobile code is envisioned in future GRIDs which allows service creation and deployment on arbitrary nodes of a GRID. Dynamic Grid structures become an important point for the use of mobile code.

Decay kinetics and quantum yields of fluorescence in photosystem I from Synechococcus elongatus with P700 in the reduced and oxidized state: are the kinetics of excited state decay trap-limited or transfer-limited?

Transfer and trapping of excitation energy in photosystem I (PS I) trimers isolated from Synechococcus elongatus have been studied by an approach combining fluorescence induction experiments with picosecond time-resolved fluorescence measurements, both at room temperature (RT) and at low temperature (5 K). Special attention was paid to the influence of the oxidation state of the primary electron donor P700. A fluorescence induction effect has been observed, showing a approximately 12% increase in fluorescence quantum yield upon P700 oxidation at RT, whereas at temperatures below 160 K oxidation of P700 leads to a decrease in fluorescence quantum yield ( approximately 50% at 5 K). The fluorescence quantum yield for open PS I (with P700 reduced) at 5 K is increased by approximately 20-fold and that for closed PS I (with P700 oxidized) is increased by approximately 10-fold, as compared to RT. Picosecond fluorescence decay kinetics at RT reveal a difference in lifetime of the main decay component: 34 +/- 1 ps for open PS I and 37 +/- 1 ps for closed PS I. At 5 K the fluorescence yield is mainly associated with long-lived components (lifetimes of 401 ps and 1.5 ns in closed PS I and of 377 ps, 1.3 ns, and 4.1 ns in samples containing approximately 50% open and 50% closed PS I). The spectra associated with energy transfer and the steady-state emission spectra suggest that the excitation energy is not completely thermally equilibrated over the core-antenna-RC complex before being trapped. Structure-based modeling indicates that the so-called red antenna pigments (A708 and A720, i.e., those with absorption maxima at 708 nm and 720 nm, respectively) play a decisive role in the observed fluorescence kinetics. The A720 are preferentially located at the periphery of the PS I core-antenna-RC complex; the A708 must essentially connect the A720 to the reaction center. The excited-state decay kinetics turn out to be neither purely trap limited nor purely transfer (to the trap) limited, but seem to be rather balanced.

Oxidation states of the manganese cluster during the flash-induced S-state cycle of the photosynthetic oxygen-evolving complex.

The Mn K-edge x-ray absorption spectra for the pure S states of the tetranuclear Mn cluster of the oxygen-evolving complex of photosystem II during flash-induced S-state cycling have been determined. The relative S-state populations in samples given 0, 1, 2, 3, 4, or 5 flashes were determined from fitting the flash-induced electron paramagnetic resonance (EPR) multiline signal oscillation pattern to the Kok model. The edge spectra of samples given 0, 1, 2, or 3 flashes were combined with EPR information to calculate the pure S-state edge spectra. The edge positions (defined as the zero-crossing of the second derivatives) are 6550.1, 6551.7, 6553.5, and 6553.8 eV for S0, S1, S2, and S3, respectively. In addition to the shift in edge position, the S0--> S1 and S1--> S2 transitions are accompanied by characteristic changes in the shape of the edge, both indicative of Mn oxidation. The edge position shifts very little (0.3 eV) for the S2--> S3 transition, and the edge shape shows only subtle changes. We conclude that probably no direct Mn oxidation is involved in this transition. The proposed Mn oxidation state assignments are as follows: S0 (II, III, IV, IV) or (III, III, III, IV), S1 (III, III, IV, IV), S2 (III, IV, IV, IV), S3 (III, IV, IV, IV).

Structural consequences of ammonia binding to the manganese center of the photosynthetic oxygen-evolving complex: an X-ray absorption spectroscopy study of isotropic and oriented photosystem II particles.

The structure and orientation of the manganese complex in NH3-treated photosystem II (PS II) membrane particles of spinach are being studied by X-ray absorption spectroscopy. On the basis of earlier work by our group, a structure for the tetranuclear manganese complex of PS II, which consists of two di-mu-oxo-bridged binuclear Mn units linked by a mono-mu-oxo group, has been proposed [Yachandra, V. K., et al. (1993) Science 260, 675-679]. The extended X-ray absorption fine structure (EXAFS) of the complex modified by NH3 binding in the S2-state is suggestive of an increase in the Mn-Mn distance of one of these units from 2.72 +/- 0.02 to 2.87 +/- 0.02 A, whereas the Mn-Mn distance of the second unit seems to be unaffected by NH3 treatment. The elongation of one binuclear center could result from the replacement of one bridging mu-oxo by an amido group. The lengthening of one Mn-Mn distance means that, by NH3 treatment, the distance degeneracy of the 2.7 A Mn-Mn EXAFS interaction is removed. Consequently, the orientation of individual binuclear units with respect to the membrane normal becomes resolvable by EXAFS spectroscopy of partially oriented PS II membrane particles. The angle between the normal of the PS II-containing membrane and the Mn-Mn vector is determined to be 67 degrees +/- 3 degrees for the 2.87 A distance and 55 degrees +/- 4 degrees for the 2.72 A distance. Only small effects on position, shape, and orientation dependence of Mn K-edge spectra result from NH3 treatment, indicating that the Mn oxidation state, the symmetry of the Mn ligand environment, and the orientation of the complex remain essentially unaffected in the annealed NH3 S2-state. Therefore, it seems likely that the angles determined for the ammonia-modified manganese complex are similar to the respective angles of the untreated complex. The structure of the manganese complex and its orientation in the membrane are discussed.

Correlation between structure and magnetic spin state of the manganese cluster in the oxygen-evolving complex of photosystem II in the S2 state: determination by X-ray absorption spectroscopy.

The structure of the manganese cluster in the S2 state with the g approximately 4 EPR signal (S2-g4 state) generated by 130 K illumination of photosystem II (PSII) membranes prepared from spinach has been investigated by X-ray absorption spectroscopy. The Mn X-ray absorption K-edge spectra of the S2-g4 state not only show a shift of the inflection point to higher energy from the S1 state but also reveal a different edge shape from that of the S2 state with the multiline signal (S2-MLS state). Extended X-ray absorption fine structure (EXAFS) studies of the Mn K-edge show that the structure of the Mn cluster in the S2-g4 state is distinctly different from those in the S2-MLS or S1 states. In the S2-g4 state, the second shell of back-scatters from the Mn absorber is found to contain two Mn-Mn distances of 2.73 and 2.85 A. We interpret this to indicate the presence of two nonequivalent di-mu-oxo-bridged Mn binuclear structures in the Mn cluster of the S2-g4 state. The third shell of the S2-g4 state at about 3.3 A also contains increased heterogeneity. By contrast, very little distance disorder was found to exist in the second shell of the S1 or S2-MLS states. A mechanism is proposed to explain these results in the context of our model for the Mn cluster and the EPR properties of the Mn complex in the S2 state.

Global target analysis of picosecond chlorophyll fluorescence kinetics from pea chloroplasts: A new approach to the characterization of the primary processes in photosystem II alpha- and beta-units.

In this study, we have used the method of target analysis to analyze the ps fluorescence kinetics of pea chloroplasts with open (F(0)) and closed (F(max)) photosystem II (PS II) centers. Extending the exciton/radical pair equilibrium model (Schatz, G. H., H. Brock, and A. R. Holzwarth. 1988. Biophys. J. 54:397-405) to allow for PS II heterogeneity, we show that two types of PS II (labeled alpha and beta) must be accounted for, each pool being characterized by its own set of molecular rate constants within the model. Simultaneous global target analysis of the data at F(0) and F(max) results in a detailed description of the molecular kinetics and energetics of the primary processes in both types of PS II units. This characterization revealed that the PS IIalpha pool accounts for twice as many Chl molecules as PS IIbeta, which suggests a PSIIalpha/PSIIbeta reaction center stoichiometry of close to unity. By extrapolation it is shown that the primary charge separation in hypothetical "isolated" beta reaction centers is slower than in isolated alpha reaction centers: in open centers by a factor of 4 (1/k(1) (int) = 11 vs 2.9 ps), in closed centers by a factor of 2 (1/k(1) (int) = 34 vs 19 ps). Despite this slower charge separation process in PS IIbeta, the quantum efficiency of the charge separation process is hardly affected: a charge stabilization yield at F(0), (i.e., P(+)IQ(A) (-)) of 86% (as compared to 90% in PS IIalpha). Reduction of Q(A) (closing PS II) has distinctly different effects on the primary kinetics of PS IIbeta, as compared to PS IIalpha. In PS IIalpha the charge separation rate drops by a factor of 6, whereas the charge recombination process is hardly affected. In PS IIbeta the charge separation is slowed down by a factor of 3, whereas the charge recombination rate increases by a factor of 5. In terms of changes in standard free energy, the reduction to Q(A) (-) lifts the free energy of the radical pair P(+)I(-), relative to the excited state (Chl(n)/P)(*), by 47 meV in PS IIalpha and by 67 meV in PS IIbeta. The concomitant increase in fluorescence quantum yield is the same for both types of PS II. These results show that PS IIalpha and PS IIbeta exhibit a different molecular functioning with respect to the primary processes, which might have its origin in a different molecular structure of the reaction centers and/or a different local environment of these centers. Location in different parts of the thylakoid membrane might be involved. We also applied different error analysis procedures to determine the error ranges of the values found for the molecular rate constants. It is shown that the commonly used standard error has very little meaning, as it assumes independence of the fit parameters. Instead, an exhaustive search procedure, accounting for all possible correlations between the fit parameters, gives a more realistic view on the accuracy of the fit parameters.

In search of a putative long-lived relaxed radical pair state in closed photosystem II: Kinetic modeling of picosecond fluorescence data.

The concept of a relaxed radical pair state in closed photosystem (PS) II centers (first quinone acceptor reduced) is critically examined on the basis of chlorophyll fluorescence decay data of the green alga Scenedesmus obliquus. Global analysis resulting in the decay-associated fluorescence spectra from closed PS II centers reveals a new PS II lifetime component (tau approximately 380 ps) in addition to two PS II components (tau approximately 1.3 and 2.1 ns) resolved earlier. Particular emphasis was given to resolve a potential long-lived ( approximately 10 ns) component of small amplitude; however, the longest lifetime found is only 2.1 ns. From comparison of experimental and simulated data we conclude that the maximum relative amplitude of such a potential long-lived component must be <0.1%. The PS II kinetics are analyzed in terms of a three-state model involving an antenna/reaction center excited state, a primary radical pair state, and a relaxed radical pair state. The rate constants for charge separation and presumed radical pair relaxation as well as those for the reverse processes are calculated. Critical examination of these results leads us to exclude the formation with high yield (> 15%) of a long-lived (tau >/= 3 ns) relaxed radical pair in closed PS II. If at all distinguishable kinetically and energetically from the primary radical pair, a relaxed radical pair would not live longer than 2-3 ns in green algae. The data suggest, however, that the concept of a long-lived relaxed radical pair state is inappropriate for intact PS II.