Observation of a bacteriochlorophyll anion radical during the primary charge separation in a reaction center

The primary light-induced charge separation in reaction centers of Rhodobacter sphaeroides was investigated with femtosecond time resolution. The absorption changes in the time range 100 fs to 1 ns observed after direct excitation of the primary donor P at 860 nm could only be explained by a kinetic model which uses three time constants. This finding supports the following reaction scheme: (i) the electronically excited primary donor P* decays with a time constant of 3.5 ps and populates a very short-lived intermediate involving a reduced accessory bacteriochlorophyll molecule; (ii) with a time constant of 0.9 ps the electron is transferred to the neighboring bacteriopheophytin molecule; and (iii) from there within 200 ps to the quinone

Initial electron-transfer in the reaction center from Rhodobacter sphaeroides.

The initial electron transfer steps in the photosynthetic reaction center of the purple bacterium Rhodobacter sphaeroides have been investigated by femtosecond time-resolved spectroscopy. The experimental data taken at various wavelengths demonstrate the existence of at least four intermediate states within the first nanosecond. The difference spectra of the intermediates and transient photodichroism data are fully consistent with a sequential four-step model of the primary electron transfer: Light absorption by the special pair P leads to the state P*. From the excited primary donor P*, the electron is transferred within 3.5 +/- 0.4 ps to the accessory bacteriochlorophyll B. State P+B- decays with a time constant of 0.9 +/- 0.3 ps passing the electron to the bacteriopheophytin H. Finally, the electron is transferred from H- to the quinone QA within 220 +/- 40 ps

Protein/lipid interactions in phospholipid monolayers containing the bacterial antenna protein B800-850

Studies on monomolecular layers of phospholipids containing the antenna protein B800-850 (LHCP) and in some cases additionally the reaction center of the photosynthetic bacterium Rhodopseudomonas sphaeroides are reported. Information on monolayer preparation as well as on protein /lipid and protein/protein interaction is obtained by means of fluorescence spectroscopy and microscopy at the air/water interface in combination with film balance experiments. It is shown that a homogeneous distribution of functional proteins can be achieved. This can be transformed into a regular pattern-like distribution by inducing a phospholipid phase transition. Although the LHCP preferentially partitions into the fluid lipid phase, it decreases the lateral pressure necessary to crystallize the lipid. This is probably due to an increase in order of the fluid phase. A pressure-induced conformation change of the LHCP is detected via a drastic change in fluorescence yield. A highly efficient energy transfer from LHCP to the reaction center is observed. This proves the quantitative reconstitution of both types of proteins and indicates protein aggregation also in the monolayer

The accessory bacteriochlorophyll

The primary electron transfer in reaction centers of Rhodobacter sphaeroides is studied by subpicosecond absorption spectroscopy with polarized light in the spectral range of 920-1040 nm. Here the bacteriochlorophyll anion radical has an absorption band while the other pigments of the reaction center have vanishing ground-state absorption. The transient absorption data exhibit a pronounced 0.9-ps kinetic component which shows a strong dichroism. Evaluation of the data yields an angle between the transition moments of the special pair and the species related with the 0.9-ps kinetic component of 26 +/- 8 degrees. This angle compares favorably with the value of 29 degrees expected for the reduced accessory bacteriochlorophyll. Extensive transient absorbance data are fully consistent with a stepwise electron transfer via the accessory bacteriochlorophyll

EPR, ENDOR, and TRIPLE resonance studies of modified bacteriochlorophyll cation radicals

A series of substituted bacteriochlorophyll molecules, all used in reconstitution experiments of reaction centers of Rhodobacter sphaeroides (Struck et al. Biochim. Biophys. Acta 1991, 1060, 262-270), were characterized by EPR, electron-nuclear double (ENDOR), and electron-nuclear-nuclear triple (TRIPLE) resonance spectroscopy in their monomeric radical cation states. Effects of different substituents at position 3 in the porphyrin macrocycle were considered, especially for two «crosslinks» between plant and bacterial chlorophylls. These are 3-vinylbacteriochlorophyll where the «bacteria» acetyl group at position 3 was substituted by vinyl and 3-acetylchlorophyll where the «plant» vinyl group was substituted by acety

Untersuchungen über den Spaltverlust von deckbandlosen axialen Pumpenbeschaufelungen

Axial-flow pumps and compressors are usually designed without shroudring. Thus, a flow round the blade-tips is possible and can essentially influence the flow-conditions. This paper deals with the problems which arise in connection with this flow round the bladetips. Results of tests on an one-stage axialflow pump with gradually widened tip-clearance are presented, which are compared with the results, that can be found in the literature