Evidence for a Very Early Intermediate in Bacterial Photosynthesis. A Photon-Echo and Hole-Burning Study of the Primary Donor Band in Rhodopseudomonas Sphaeroides

Two coherent spectroscopic methods, accumulated photon echo and population bottleneck hole-burning, have been employed in a study of the decay rate of the primary donor (P) of Rhodopseudomonas sphaeroides at 1.5 K. The decay rate is instrument-limited in the photon-echo experiment, implying a population relaxation time <100 fs. The hole-burning study revealed the P absorplion at 900 nm to be largely homogeneousy broadened, from which a decay time of ≈25 fs was inferred. Comparison of these data with a photon-echo study of the bacteriochlorophyll a monomer suggests that this ultrafast process is not due to vibrational relaxation within P*, but to an excited state electronic decay mechanism. It is suggested that the initial event after excitation in P is a very rapid charge separation within the dimer pair, prior to the electron-transfer process, which occurs on a much longer timescale

Light-induced structural changes in photosynthetic reaction centres studied by ESEEM of spin-correlated D+QA− radical pairs

AbstractZn-substituted Rhodobacter sphaeroides R26 reaction centres (RCs) frozen in the dark and under illumination exhibit quite different recombination kinetics of the D+QA− radical pairs [Kleinfeld et al., Biochemistry, 23 (1984) 5780]. We have applied electron spin echo envelope modulation (ESEEM) of the spin-correlated D+QA− radical pairs to assess a possible light-induced change in the distance between the D and QA cofactors. The recombination kinetics and the field-swept spin-polarized EPR signal for the two preparations have been monitored by time-resolved EPR spectroscopy. For the samples frozen under illumination, a slight increase in the distance, 0.4±0.2 Å, has been detected

Formation of a Long-Lived P Ba-State in Plant Pheophytin-Exchanged Reaction Centers of Rhodobacter sphaeroides R26 at Low Temperature

Femtosecond transient absorption spectroscopy in the range of 500-1040 nm was used to study electron transfer at 5 K in reaction centers of Rhodobacter sphaeroides R26 in which the bacteriopheophytins (BPhe) were replaced by plant pheophytin a (Phe). Primary charge separation took place with a time constant of 1.6 ps, similar to that found in native RCs. Spectral changes around 1020 nm indicated the formation of reduced bacteriochlorophyll (BChl) with the same time constant, and its subsequent decay in 620 ps. This observation identifies the accessory BChl as the primary electron acceptor. No evidence was found for electron transfer to Phe, indicating that electron transfer from B(A

ESR, ENDOR and TRIPLE resonance studies of the primary donor radical cation P960+ in the photosynthetic bacterium Rhodopseudomonas viridis

The light-induced radical cation of the primary electron donor P960+• in photosynthetic reaction centers from Rhodopseudomonas viridis has been investigated by ESR, ENDOR and TRIPLE techniques. Both the comparison with the cation radical of monomeric bacteriochlorophyll b (BChl b) and with molecular-orbital calculations performed on P960+• using the results of an X-ray structure analysis, consistently show an asymmetric distribution of the unpaired electron over the two BChl b molecules which constitute P960+•. The possible relevance of this result for the primary electron transfer step in the reaction center is briefly discussed

National implementation of an optimal standardised technique for right-sided colon cancer:protocol of an interventional sequential cohort study (Right study)

Purpose: Minimally invasive right hemicolectomy (MIRH) is the cornerstone of treatment for patients with right-sided colon cancer. This operation has evolved during recent decades, with many innovations and improvements but this has also resulted in high variability of uptake with subsequent substantial variableness. The aim of this ongoing study is to identify current surgical variations, determine the most optimal and standardised MIRH and nationally train and implement that technique to improve short-term clinical and long-term oncological outcomes. Methods: The Right study is a national multicentre prospective interventional sequential cohort study. Firstly, current local practice was evaluated. Subsequently, a standardised surgical technique for right-sided colon cancer was determined using the Delphi consensus method, and this procedure was trained during hands-on courses. The standardised MIRH will be implemented with proctoring (implementation cohort), after which the performance will be monitored (consolidation cohort). Patients who will receive a minimally invasive (extended) right hemicolectomy for cT1-3N0-2M0 colon cancer will be included. The primary outcome is patient safety reflected in the 90-day overall complication rate according to the Clavien–Dindo classification. Secondary outcomes will include intraoperative complications, 90-day mortality rate, number of resected tumour-positive lymph nodes, completeness of mesocolic excision, surgical quality score, locoregional and distant recurrence and 5-year overall survival. A total number of 1095 patients (365 per cohort) will be included. Discussion: The Right study is designed to safely implement the best surgical practice concerning patients with right-sided colon cancer aiming to standardise and improve the surgical quality of MIRH at a national level. Trial registration: ClinicalTrials.gov: NCT04889456, May 2021.</p

Magic-angle spinning 13C NMR with atomic resolution of a photosynthetic reaction center enriched in [4'-13]tyrosine

Bio-organic Synthesi

13C Magic angle spinning NMR characterization of the functionally asymmetric QA binding in Rhodobacter sphaeroides R26 photosynthetic reaction centers using site-specific 13C-labeled ubiquinone-10

Bio-organic SynthesisBiological and Soft Matter Physic

Carbon-13 magic angle spinning NMR study of the light-induced and temperature-dependent changes in Rhodbacter sphaeroides R26 reaction centers enriched in [4'-13C]tyrosine

Bio-organic Synthesi

FTIR spectroscopy shows weak symmetric hydrogen bonding of the Q_B carbonyl groups in Rhodobacter sphaeroides R26 reaction centres

Bio-organic Synthesi