Identification of the first steps in charge separation in bacterial photosynthetic reaction centers of Rhodobacter sphaeroides by ultrafast mid-infrared spectroscopy: Electron transfer and protein dynamics

AbstractTime-resolved visible pump/mid-infrared (mid-IR) probe spectroscopy in the region between 1600 and 1800cm−1 was used to investigate electron transfer, radical pair relaxation, and protein relaxation at room temperature in the Rhodobacter sphaeroides reaction center (RC). Wild-type RCs both with and without the quinone electron acceptor QA, were excited at 600nm (nonselective excitation), 800nm (direct excitation of the monomeric bacteriochlorophyll (BChl) cofactors), and 860nm (direct excitation of the dimer of primary donor (P) BChls (PL/PM)). The region between 1600 and 1800cm−1 encompasses absorption changes associated with carbonyl (CO) stretch vibrational modes of the cofactors and protein. After photoexcitation of the RC the primary electron donor P excited singlet state (P*) decayed on a timescale of 3.7ps to the state P+BL− (where BL is the accessory BChl electron acceptor). This is the first report of the mid-IR absorption spectrum of P+BL−; the difference spectrum indicates that the 9-keto CO stretch of BL is located around 1670–1680cm−1. After subsequent electron transfer to the bacteriopheophytin HL in ∼1ps, the state P+HL− was formed. A sequential analysis and simultaneous target analysis of the data showed a relaxation of the P+HL− radical pair on the ∼20ps timescale, accompanied by a change in the relative ratio of the PL+ and PM+ bands and by a minor change in the band amplitude at 1640cm−1 that may be tentatively ascribed to the response of an amide CO to the radical pair formation. We conclude that the drop in free energy associated with the relaxation of P+HL−, is due to an increased localization of the electron hole on the PL half of the dimer and a further consequence is a reduction in the electrical field causing the Stark shift of one or more amide CO oscillators

Electron Transfer from Cyt b559 and Tyrosine-D to the S2 and S3 states of the water oxidizing complex in Photosystem II at Cryogenic Temperatures

The Mn4CaO5 cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with Tyrosine(Z) and P-680, which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine(D) (Y-D) and Cytochrome b (559) (Cyt b (559)) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b (559) and Y-D to the S-2 and S-3 states at 195 K. First, Y-D (aEuro cent) and Cyt b (559) were chemically reduced. The S-2 and S-3 states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S-1 state. EPR signals of the WOC (the S-2-state multiline signal, ML-S-2), Y-D (aEuro cent) and oxidized Cyt b (559) were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S-2 population decayed to S-1 in the S-2 samples by following a single exponential decay. Differently, S-3 samples showed an initial increase in the ML-S-2 intensity (due to S-3 to S-2 conversion) and a subsequent slow decay due to S-2 to S-1 conversion. In both cases, only a minor oxidation of Y-D was observed. In contrast, the signal intensity of the oxidized Cyt b (559) showed a two-fold increase in both the S-2 and S-3 samples. The electron donation from Cyt b (559) was much more efficient to the S-2 state than to the S-3 state

Günstiger Verlauf eines persistierenden malignen Aszites

Malignant ascites is a frequent complication in oncological diseases. There are no standard therapies for any primary tumour. We report the case of a woman, aged 49 years at the time of primary diagnosis, who suffered from recurrent ascites resulting from liver metastasis of breast cancer. Based on the literature and former experience of our department, mistletoe extract was repeatedly applied intraperitoneally at the occasion of decompressive punctures. The further course of the disease suggests a significant role of mistletoe in achieved symptom control, which also resulted in a considerable improvement in quality of life. The mistletoe solution was well tolerated. Relevant mechanisms of action in addition to the well-known immunomodulating properties of mistletoe could be direct cytotoxic and adjuvant effects to the concomitantly administered chemotherapy of carboplatin/paclitaxel

Energy transfer and charge separation in photosystem I: P700 oxidationupon selective excitation of the long-wavelength antenna chlorophyllsof Synechococcus elongatus

Photosystem I of the cyanobacterium Synechococcus elongatus contains two spectral pools of chlorophylls called C-708 and C-719 that absorb at longer wavelengths than the primary electron donor P700. We investigated the relative quantum yields of photochemical charge separation and fluorescence as a function of excitation wavelength and temperature in trimeric and monomeric photosystem I complexes of this cyanobacterium. The monomeric complexes are characterized by a reduced content of the C-719 spectral form. At room temperature, an analysis of the wavelength dependence of P700 oxidation indicated that all absorbed light, even of wavelengths of up to 750 nm, has the same probability of resulting in a stable P700 photooxidation. Upon cooling from 295 K to 5 K, the nonselectively excited steady-state emission increased by 11- and 16-fold in the trimeric and monomeric complexes, respectively, whereas the quantum yield of P700 oxidation decreased 2.2- and 1.7-fold. Fluorescence excitation spectra at 5 K indicate that the fluorescence quantum yield further increases upon scanning of the excitation wavelength from 690 nm to 710 nm, whereas the quantum yield of P700 oxidation decreases significantly upon excitation at wavelengths longer than 700 nm. Based on these findings, we conclude that at 5 K the excited state is not equilibrated over the antenna before charge separation occurs, and that approximately 50% of the excitations reach P700 before they become irreversibly trapped on one of the long-wavelength antenna pigments. Possible spatial organizations of the long-wavelength antenna pigments in the three-dimensional structure of photosystem I are discussed