M281, an Anti-FcRn Antibody: Pharmacodynamics, Pharmacokinetics, and Safety Across the Full Range of IgG Reduction in a First-in-Human Study.

M281 is a fully human, anti-neonatal Fc receptor (FcRn) antibody that inhibits FcRn-mediated immunoglobulin G (IgG) recycling to decrease pathogenic IgG while preserving IgG production. A randomized, double-blind, placebo-controlled, first-in-human study with 50 normal healthy volunteers was designed to probe safety and the physiological maximum for reduction of IgG. Intravenous infusion of single ascending doses up to 60 mg/kg induced dose-dependent serum IgG reductions, which were similar across all IgG subclasses. Multiple weekly doses of 15 or 30 mg/kg achieved mean IgG reductions of ≈85% from baseline and maintained IgG reductions ≥75% from baseline for up to 24 days. M281 was well tolerated, with no serious or severe adverse events (AEs), few moderate AEs, and a low incidence of infection-related AEs similar to placebo treatment. The tolerability and consistency of M281 pharmacokinetics and pharmacodynamics support further evaluation of M281 in diseases mediated by pathogenic IgG.

Safety, tolerability, and pharmacology of AB928, a novel dual adenosine receptor antagonist, in a randomized, phase 1 study in healthy volunteers.

Adenosine suppresses antitumor immune responses via A2a and A2b receptors expressed on intratumoral immune cells. This effect is mediated by increased cyclic adenosine 5'-monophosphate (AMP) levels and phosphorylation of cyclic AMP response element binding protein (CREB). We conducted a phase 1, placebo-controlled, single-ascending-dose (SAD) and multiple-ascending-dose (MAD) study to assess the safety, tolerability, pharmacokinetics (PK), including food effect (FE), and pharmacodynamics (PD) of oral AB928, a novel dual A2aR/A2bR antagonist, in healthy volunteers. AB928 doses between 10 and 200 mg once daily and 100 mg twice daily were evaluated. The study enrolled 85 subjects (randomized 3:1, AB928:placebo), 40 each in the SAD and MAD cohorts, and 5 in the FE cohort. AB928 was well tolerated up to the highest dose tested and did not affect any physiologic parameters potentially sensitive to adenosine inhibition. No safety concern was identified. The PK profile of AB928 was linear and dose-proportional, and a clear PK/PD correlation was demonstrated. Significant inhibition of adenosine receptor-mediated phosphorylated CREB was observed at peak plasma concentrations in all dose cohorts and at trough plasma concentrations in the higher-dose cohorts. AB928 plasma levels ≥1 µM were associated with ≥90% adenosine receptor inhibition. In the postprandial state, the rate of AB928 absorption decreased but the extent of absorption was unchanged. Together, these data support further clinical development of oral AB928 in cancer patients.

A pharmacokinetics and pharmacodynamics equivalence trial of the proposed pegfilgrastim biosimilar, MYL-1401H, versus reference pegfilgrastim.

PURPOSE: Pegfilgrastim is a long-acting granulocyte colony-stimulating factor indicated for prevention of febrile neutropenia in patients receiving myelosuppressive chemotherapy by promoting neutrophil recovery. METHODS: This phase 1, randomized, double-blind, three-way crossover trial in healthy volunteers evaluated the pharmacokinetics (PK), pharmacodynamics (PD), safety, and tolerability of the proposed biosimilar, comparing MYL-1401H, reference pegfilgrastim (Neulasta®, Amgen Inc, Thousand Oaks, CA, USA) sourced from the European Union, and reference pegfilgrastim sourced from the USA. Primary PK end points were peak plasma concentration of pegfilgrastim (Cmax) and area under the plasma concentration-time curve from the time of dosing to infinity (AUC0-inf). Primary PD end points were area under the curve above baseline for absolute neutrophil counts (ANC AUC0-t) and maximum change from baseline for ANC (ANC Cmax). Adverse events were also recorded. RESULTS: The primary PK and PD end points were similar across all groups. For the PK parameters, the 90% confidence intervals (CIs) of the ratios of geometric means ranged between 0.91 and 1.18, which were within the predefined bioequivalence interval of 0.8000 to 1.2500 for all comparisons. For the PD parameters, the 95% CIs of the ratios of geometric means ranged between 0.94 and 1.06 for all comparisons, which were within the predefined PD equivalence interval of 0.8500 to 1.1765. The safety profiles were similar, with the most common adverse events being back pain and headache. CONCLUSIONS: MYL-1401H demonstrated similar PK, PD, and safety to reference pegfilgrastim in healthy volunteers and may be an equivalent option for the prevention of febrile neutropenia.

Safety, tolerability and pharmacodynamics of apical sodium-dependent bile acid transporter inhibition with volixibat in healthy adults and patients with type 2 diabetes mellitus: a randomised placebo-controlled trial.

BACKGROUND: Pathogenesis in non-alcoholic steatohepatitis (NASH) involves abnormal cholesterol metabolism and hepatic accumulation of toxic free cholesterol. Apical sodium-dependent bile acid transporter (ASBT) inhibition in the terminal ileum may facilitate removal of free cholesterol from the liver by reducing recirculation of bile acids (BAs) to the liver, thereby stimulating new BA synthesis from cholesterol. The aim of this phase 1 study in adult healthy volunteers (HVs) and patients with type 2 diabetes mellitus (T2DM) was to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of ASBT inhibition with volixibat (SHP626; formerly LUM002). METHODS: Participants were randomised 3:1 to receive once-daily oral volixibat (0.5 mg, 1 mg, 5 mg or 10 mg) or placebo for 28 days in two cohorts (HV and T2DM). Assessments included safety, faecal BA and serum 7α-hydroxy-4-cholesten-3-one (C4; BA synthesis biomarker). RESULTS: Sixty-one individuals were randomised (HVs: placebo, n = 12; volixibat, n = 38; T2DM: placebo, n = 3; volixibat, n = 8). No deaths or treatment-related serious adverse events were reported. Mild or moderate gastrointestinal adverse events were those most frequently reported with volixibat. With volixibat, mean total faecal BA excretion on day 28 was ~1.6-3.2 times higher in HVs (643.73-1239.3 µmol/24 h) and ~8 times higher in T2DM (1786.0 µmol/24 h) than with placebo (HVs: 386.93 µmol/24 h; T2DM: 220.00 µmol/24 h). With volixibat, mean C4 concentrations increased by ~1.3-5.3-fold from baseline to day 28 in HVs and by twofold in T2DM. CONCLUSIONS: Volixibat was generally well tolerated. Increased faecal BA excretion and serum C4 levels support the mechanistic rationale for exploring ASBT inhibition in NASH. The study was registered with the Dutch clinical trial authority (Centrale Commissie Mensgebonden Onderzoek; trial registration number NL44732.056.13; registered 24 May 2013).

Transient CDK4/6 inhibition protects hematopoietic stem cells from chemotherapy-induced exhaustion.

Conventional cytotoxic chemotherapy is highly effective in certain cancers but causes dose-limiting damage to normal proliferating cells, especially hematopoietic stem and progenitor cells (HSPCs). Serial exposure to cytotoxics causes a long-term hematopoietic compromise ("exhaustion"), which limits the use of chemotherapy and success of cancer therapy. We show that the coadministration of G1T28 (trilaciclib), which is a small-molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), contemporaneously with cytotoxic chemotherapy protects murine hematopoietic stem cells (HSCs) from chemotherapy-induced exhaustion in a serial 5-fluorouracil treatment model. Consistent with a cell-intrinsic effect, we show directly preserved HSC function resulting in a more rapid recovery of peripheral blood counts, enhanced serial transplantation capacity, and reduced myeloid skewing. When administered to healthy human volunteers, G1T28 demonstrated excellent in vivo pharmacology and transiently inhibited bone marrow (BM) HSPC proliferation. These findings suggest that the combination of CDK4/6 inhibitors with cytotoxic chemotherapy should provide a means to attenuate therapy-induced BM exhaustion in patients with cancer.

Model based analysis of transient fluorescence yield induced by actinic laser flashes in spinach leaves and cells of green alga Chlorella pyrenoidosa Chick.

Measurements of Single Flash Induced Transient Fluorescence Yield (SFITFY) on spinach leaves and whole cells of green thermophilic alga Chlorella pyrenoidosa Chick were analyzed for electron transfer (ET) steps and coupled proton transfer (PT) on both the donor and the acceptor side of the reaction center (RC) of photosystem II (PS II). A specially developed PS II model (Belyaeva et al., 2008, 2011a) allowed the determination of ET steps that occur in a hierarchically ordered time scale from nanoseconds to several seconds. Our study demonstrates that our SFITFY data is consistent with the concept of the reduction of P680(+) by YZ in both leaves and algae (studied on spinach leaves and cells of Chlorella pyrenoidosa Chick). The multiphasic P680(+) reduction kinetics by YZ in PS II core complexes with high oxygen evolution capacity was seen in both algae and leaves. Model simulation to fit SFITFY curves for dark adapted species used here gives the rate constants to verify nanosecond kinetic stages of P680(+) reduction by YZ in the redox state S1 of the water oxidizing complex (WOC) shown in Kühn et al. (2004). Then a sequence of relaxation steps in the redox state S1, outlined by Renger (2012), occurs in both algae and leaves as a similar non-adiabatic ET reactions. Coupled PT is discussed briefly to understand a rearrangement of hydrogen bond protons in the protein matrix of the WOC (Umena et al., 2011). On the other hand, present studies showed a slower reoxidation of reduced QA by QB in algal cells as compared with that in a leaf that might be regarded as a consequence of differences of spatial domains at the QB-site in leaves compared to algae. Our comparative study helped to correlate theory with experimental data for molecular photosynthetic mechanisms in thylakoid membranes.

Half-life prolongation of therapeutic proteins by conjugation to ATIII-binding pentasaccharides: a first-in-human study of CarboCarrier® insulin.

AIM: Conjugation to antithrombin III ATIII-binding pentasaccharides has been proposed as a novel method to extend the half-life of therapeutic proteins. We aim to validate this technological concept in man by performing a first-in-human study using CarboCarrier® insulin (SCH 900948) as an example. A rising single dose phase 1 study was performed assessing safety, tolerability, pharmacokinetics and relative bioactivity of CarboCarrier® insulin. Safety, tolerability and pharmacokinetics (PK) of single doses of CarboCarrier® insulin in healthy volunteers were explored, and the dose-response relationship and relative bioactivity of CarboCarrier® insulin in subjects with type 2 diabetes were investigated. METHODS: After an overnight fast, subjects were randomized to a treatment sequence. PK and pharmacodynamic (glucose, insulin and C-peptide) samples were obtained for up to 72 h post-dose. Effects of CarboCarrier® insulin were compared with those of NPH-insulin. RESULTS: CarboCarrier® insulin was safe and well-tolerated and no consistent pattern of adverse events occurred. CarboCarrier® insulin exposure (Cmax and AUC) increased proportionally with dose. The mean terminal elimination half-life ranged between 3.11 and 5.28 h. All CarboCarrier® insulin dose groups showed decreases in the mean change from baseline of plasma glucose concentrations compared with the placebo group. CONCLUSIONS: CarboCarrier® insulin is pharmacologically active showing features of insulin action in man. The elimination half-life of the molecule was clearly extended compared with endogenous insulin, indicating that conjugation to ATIII-binding pentasaccharides is a viable approach to extend the half-life of therapeutic proteins in humans. This is an important step towards validation of the CarboCarrier® technology by making use of CarboCarrier® insulin as an example.

Coupling of different isolated photosynthetic light harvesting complexes and CdSe/ZnS nanocrystals via Förster resonance energy transfer.

The present work describes results obtained on hybrid systems formed in aqueous buffer solution by self-assembly of different CdSe quantum dots (QDs) surrounded by a ZnS shell and functionalized by covering the surface with anionic and cationic groups and various isolated pigment-protein complexes from the light-harvesting antennae of photosynthetic organisms (light-harvesting complexes 1 and 2 (LH1 and LH2, respectively) from purple bacteria, phycobiliproteins (PBPs) from cyanobacteria and the rod-shaped PBP from the cyanobacterium Acaryochloris marina). Excitation energy transfer (EET) from QDs to PBP rods was found to take place with varying and highly temperature-dependent efficiencies of up to 90%. Experiments performed at room temperature on hybrid systems with different QDs show that no straightforward correlation exists between the efficiency of EET and the parameter J/(R(12)(6)) given by the theory of Förster resonance energy transfer (FRET), where J is the overlap integral of the normalized QD emission and PBP absorption and R(12) the distance between the transition dipole moments of donor and acceptor. The results show that the hybrid systems cannot be described as randomly orientated aggregates consisting of QDs and photosynthetic pigment-protein complexes. Specific structural parameters are inferred to play an essential role. The mode of binding and coupling seems to change with the size of QDs and with temperature. Efficient EET and fluorescence enhancement of the acceptor was observed at particular stoichiometric ratios between QDs and trimeric phycoerythrin (PE). At higher concentrations of PE, a quenching of its fluorescence is observed in the presence of QDs. This effect is explained by the existence of additional quenching channels in aggregates formed within hybrid systems. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Pharmacodynamics and pharmacokinetics of the novel PAR-1 antagonist vorapaxar (formerly SCH 530348) in healthy subjects.

PURPOSE: The aim of our study was to evaluate the pharmacology of vorapaxar (SCH 530348), an oral PAR-1 antagonist, in healthy volunteers. METHODS AND RESULTS: In two randomized, placebo-controlled studies, subjects received either single ascending doses of vorapaxar (0.25, 1, 5, 10, 20, or 40 mg; n = 50), multiple ascending doses of vorapaxar (1, 3, or 5 mg/day for 28 days; n = 36), a loading dose (10 or 20 mg) followed by daily maintenance doses (1 mg) for 6 days (n = 12), or placebo. Single 20- and 40-mg doses of vorapaxar completely inhibited thrombin receptor activating peptide (TRAP)-induced platelet aggregation (>80% inhibition) at 1 h and sustained this level of inhibition for ≥72 h. Multiple doses yielded complete inhibition on Day 1 (5 mg/day) and Day 7 (1 and 3 mg/day). Adverse events were generally mild, transient, and unrelated to dose. CONCLUSION: Vorapaxar provided rapid and sustained dose-related inhibition of platelet aggregation without affecting bleeding or clotting times.

Excitonic energy level structure and pigment-protein interactions in the recombinant water-soluble chlorophyll protein. I. Difference fluorescence line-narrowing.

Difference fluorescence line-narrowing spectroscopy at 4.5 K was employed to investigate electron-phonon and electron-vibrational coupling strengths of the lower exciton level of water-soluble chlorophyll-binding protein (WSCP) from cauliflower reconstituted with chlorophyll a or chlorophyll b, respectively. The electron-phonon coupling is found to be moderate with integral Huang-Rhys factors S in the order of 0.81-0.85. A weak dependence of S on excitation wavelength within the inhomogeneously broadened fluorescence origin band is attributed to a sizable contribution of nonresonant excitation that varies with excitation wavelength. The strongly asymmetric and highly structured one-phonon profile is characterized by a peak phonon frequency (ω(m)) of ~24 cm(-1) and further discernible peaks at 48 and 88 cm(-1), respectively. A structural assignment of this unusual one-phonon profile is proposed. As will be shown in the accompanying paper (part II) (DOI 10.1021/jp111457t), the parameters of electron-phonon coupling readily account for shape and position of the fluorescence origin bands at 666.1 and 683.8 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. A rich structure of S(1)→S(0) vibrational frequencies was resolved in the wavenumber range between 180 and 1665 cm(-1) for both chlorophyll a- and chlorophyll b-WSCP. The corresponding individual Huang-Rhys factors fall in the range between 0.0011 and 0.0500. To the best of our knowledge, this is the first report of S-factors for vibrational modes of chlorophyll b. Most remarkable is the presence of two additional modes at 228 and 327 cm(-1) compared with the vibrational spectrum of chlorophyll in solution. The additional modes can most likely be attributed to H-bond formation in the vicinity of the chlorophyll molecule bound by WSCP.

Excitonic energy level structure and pigment-protein interactions in the recombinant water-soluble chlorophyll protein. II. Spectral hole-burning experiments.

Persistent spectral hole burning at 4.5 K has been used to investigate the excitonic energy level structure and the excited state dynamics of the recombinant class-IIa water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The hole-burned spectra are composed of four main features: (i) a narrow zero-phonon hole (ZPH) at the burn wavelength, (ii) a number of vibrational ZPHs, (iii) a broad low-energy hole at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, and (iv) a second satellite hole at ~658 and ~673 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The doublet of broad satellite holes is assigned to an excitonically coupled chlorophyll dimer. The lower-energy holes at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, represent the lower exciton states. Taking into account the parameters of electron-phonon coupling, the lower exciton state can be assigned as the fluorescence origin. The lower exciton state is populated by two processes: (i) exciton relaxation from the higher exciton state and (ii) vibrational relaxation within the lower exciton state. Assuming identical site energies for the two excitonically coupled chlorophyll molecules, the dipole-dipole interaction energy J is directly determined to be 85 and 100 cm(-1) for chlorophyll b- and chlorophyll a-WSCP, respectively, based on the positions of the satellite holes. The Gaussian low-energy absorption band identified by constant fluence hole burning at 4.5 K has a width of ~150 cm(-1) and peaks at 664.9 and 682.7 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The action spectrum is broader and blue-shifted compared to the fluorescent lower exciton state. This finding can be explained by a slow protein relaxation between energetically inequivalent conformational substates within the lowest exciton state in agreement with the results of Schmitt et al. (J. Phys. Chem. B2008, 112, 13951).

Water soluble chlorophyll binding protein of higher plants: a most suitable model system for basic analyses of pigment-pigment and pigment-protein interactions in chlorophyll protein complexes.

This short review paper describes spectroscopic studies on pigment-pigment and pigment-protein interactions of chlorophyll (Chl) a and b bound to the recombinant protein of class IIa water soluble chlorophyll protein (WSCP) from cauliflower. Two Chls form a strongly excitonically coupled open sandwich dimer within the tetrameric protein matrix. In marked contrast to the mode of excitonic coupling of Chl and bacterio-Chl molecules in light harvesting complexes and reaction centers of all photosynthetic organisms, the unique structural pigment array in the Chl dimer of WSCP gives rise to an upper excitonic state with a large oscillator strength. This property opens the way for thorough investigations on exciton relaxation processes in Chl-protein complexes. Lifetime measurements of excited singlet states show that the unusual stability towards photodamage of Chls bound to WSCP, which lack any protective carotenoid molecule, originates from a high diffusion barrier to interaction of molecular dioxygen with Chl triplets. Site selective spectroscopic methods provide a wealth of information on the interactions of the Chls with the protein matrix and on the vibronic structure of the pigments. The presented data and discussions illustrate the great potential of WSCP as a model system for systematic experimental and theoretical studies on the functionalizing of Chls by the protein matrix. It opens the way for further detailed analyses and a deeper understanding of the properties of pigment protein complexes.

PS II model based analysis of transient fluorescence yield measured on whole leaves of Arabidopsis thaliana after excitation with light flashes of different energies.

Our recently presented PS II model (Belyaeva et al., 2008) was improved in order to permit a consistent simulation of Single Flash Induced Transient Fluorescence Yield (SFITFY) traces that were earlier measured by Steffen et al. (2005) on whole leaves of Arabidopsis (A.) thaliana at four different energies of the actinic flash. As the essential modification, the shape of the actinic flash was explicitly taken into account assuming that an exponentially decaying rate simulates the time dependent excitation of PS II by the 10 ns actinic flash. The maximum amplitude of this excitation exceeds that of the measuring light by 9 orders of magnitude. A very good fit of the SFITFY data was achieved in the time domain from 100 ns to 10s for all actinic flash energies (the maximum energy of 7.5 × 10¹6 photons/(cm²flash) is set to 100%, the relative energies of weaker actinic flashes were of ∼8%, 4%, ∼1%). Our model allows the calculation and visualization of the transient PS II redox state populations ranging from the dark adapted state, via excitation energy and electron transfer steps induced by pulse excitation, followed by final relaxation into the stationary state eventually attained under the measuring light. It turned out that the rate constants of electron transfer steps are invariant to intensity of the actinic laser flash. In marked contrast, an increase of the actinic flash energy by more than two orders of magnitude from 5.4×10¹4 photons/(cm²flash) to 7.5×10¹6 photons/(cm²flash), leads to an increase of the extent of fluorescence quenching due to carotenoid triplet (³Car) formation by a factor of 14 and of the recombination reaction between reduced primary pheophytin (Phe(-)) and P680(+) by a factor of 3 while the heat dissipation in the antenna complex remains virtually constant. The modified PS II model offers new opportunities to compare electron transfer and dissipative parameters for different species (e.g. for the green algae and the higher plant) under varying illumination conditions.

[Drug interaction caused by communication problems. Rhabdomyolysis due to a combination of itraconazole and simvastatin]. / Geneesmiddelinteractie door communicatieproblemen. Rabdomyolyse door de combinatie van itraconazol en simvastatine.

A 58-year-old man, who spoke very little Dutch, had various symptoms and used several drugs including simvastatin. He was prescribed itraconazole for onychomycosis. Simvastatin was concurrently replaced with pravastatin to prevent drug interactions. However, the interaction still occurred when the pravastatin ran out, and the patient resumed taking simvastatin on his own initiative. Myalgia and muscle weakness developed after one week. The general practitioner found a strongly elevated creatine kinase level in the blood. The patient required hospitalisation for severe rhabdomyolysis. He was treated with an infusion of an ample quantity of physiological saline solution and made a full recovery. Due to the elevated risk of toxic interactions, doctors should beware of communication problems in complex patients and avoid new prescriptions not strictly required.

Thermally activated superradiance and intersystem crossing in the water-soluble chlorophyll binding protein.

The crystal structure of the class IIb water-soluble chlorophyll binding protein (WSCP) from Lepidium virginicum is used to model linear absorption and circular dichroism spectra as well as excited state decay times of class IIa WSCP from cauliflower reconstituted with chlorophyll (Chl) a and Chl b. The close agreement between theory and experiment suggests that both types of WSCP share a common Chl binding motif, where the opening angle between pigment planes in class IIa WSCP should not differ by more than 10 degrees from that in class IIb. The experimentally observed (Schmitt et al. J. Phys. Chem. B 2008, 112, 13951) decrease in excited state lifetime of Chl a homodimers with increasing temperature is fully explained by thermally activated superradiance via the upper exciton state of the dimer. Whereas a temperature-independent intersystem crossing (ISC) rate is inferred for WSCP containing Chl a homodimers, that of WSCP with Chl b homodimers is found to increase above 100 K. Our quantum chemical/electrostatic calculations suggest that a thermally activated ISC via an excited triplet state T4 is responsible for the latter temperature dependence.

Excited state dynamics in recombinant water-soluble chlorophyll proteins (WSCP) from cauliflower investigated by transient fluorescence spectroscopy.

The present study describes the fluorescence emission properties of recombinant water-soluble chlorophyll (Chl) protein (WSCP) complexes reconstituted with either Chl a or Chl b alone (Chl a only or Chl b only WSCP, respectively) or mixtures of both pigments at different stoichiometrical ratios. Detailed investigations were performed with time and space correlated ps fluorescence spectroscopy within the temperature range from 10 to 295 K. The following points were found: (a) The emission spectra at room temperature (295 K) are well characterized by bands with a dominating Lorentzian profile broadened due to phonon scattering and peak positions located at 677, 684 and 693 nm in the case of Chl a only WSCP and at 665, 675 and 689 nm for Chl b only WSCP. In addition, all spectra contain minor bands in the longer wavelength region. (b) The emission spectra at 10 K of samples suspended in buffer containing 50% glycerol are dominated by bands peaking at 668 nm for Chl b only WSCP and at 685 nm for Chl a only WSCP and samples reconstituted with mixtures of Chl a and Chl b. (c) At 10 K and in buffer with 50% glycerol the decay kinetics of WSCP samples with Chl a only are dominated by a component with a time constant of 6.2 (+/-0.2) ns at 685 nm while those of WSCP containing mixtures of Chl a and Chl b are characterized by a slightly shorter value of 6.0 (+/-0.2) ns. WSCP containing Chl b only exhibits a distinctly longer value of 7.0 (+/-0.3) ns at an emission wavelength of 668 nm. (d) The decay associated emission spectra at 10 K of all samples exhibit at least 3 decay components with time constants of 80-120 ps, 2-4 ns and 6-7 ns in 50% glycerol. These results are consistently described within the framework of our previously presented model (J. Phys. Chem. B 2007, 111, No. 46, 13325; J. Phys. Chem. B 2007, 111, No. 35, 10487) , for the structural motifs of chlorophyll binding to the tetrameric protein matrix of WSCP. It is shown that formation of strongly coupled open sandwich dimers does not lead to quenching of 1Chl a* or 1Chl b*.

PS II model-based simulations of single turnover flash-induced transients of fluorescence yield monitored within the time domain of 100 ns-10 s on dark-adapted Chlorella pyrenoidosa cells.

The set up described in Steffen et al. (Biochemistry 40:173-180, 2001) was used to monitor in the time domain from 100 ns to 10 s single turnover flash-induced transients of the normalized fluorescence yield (SFITFY) on dark-adapted cells of the thermophilic algae Chlorella pyrenoidosa Chick. Perfect data fit was achieved within the framework of a previously proposed model for the PS II reaction pattern (Lebedeva et al., Biophysics 47:968-980, 2002; Belyaeva et al., Biophysics 51:860-872, 2006) after its modification by taking into account nonradiative decay processes including nonphotochemical quenching due to time-dependent populations of P680(+*) and (3)Car. On the basis of data reported in the literature, a consistent set of rate constants was obtained for electron transfer at the donor and acceptor sides of PS II, pH in lumen and stroma, the initial redox state of plastoquinone pool and the rate of plastoquinone oxidation. The evaluation of the rate constant values of dissipative processes due to quenching by carotenoid triplets in antennae and P680(+*)Q(A)(-*) recombination as well as the initial state populations after excitation with a single laser flash are close to that outlined in (Steffen et al., Biochemistry 44:3123-3133, 2005a). The simulations based on the model of the PS II reaction pattern provide information on the time courses of population probabilities of different PS II states. We analyzed the maximum (F(m)(STF)) and minimum (F(0)) of the normalized FL yield dependence on the rate of the recombination processes (radiative and dissipative nonradiative) and of P680(+*) reduction. The developed PS II model provides a basis for theoretical comparative analyses of time-dependent fluorescence signals, observed at different photosynthetic samples under various conditions (e.g. presence of herbicides, other stress conditions, excitation with actinic pulses of different intensity, and duration).

The effect of hydration on protein flexibility in photosystem II of green plants studied by quasielastic neutron scattering.

The effect of hydration on protein dynamics in photosystem II (PS II) membrane fragments from spinach has been investigated by using the method of quasielastic neutron scattering (QENS) at room temperature. The QENS data obtained indicate that the protein dynamics is strongly dependent on the extent of hydration. In particular, the hydration-induced activation of localized diffusive protein motions and QA- reoxidation by QB in PS II appear to be correlated in their onset at a hydration value of about 45% relative humidity (r.h.). These findings underline the crucial functional relevance of localized diffusive protein motions on the picosecond-timescale for the reactions of light-induced photosynthetic water splitting under formation of plastoquinol and molecular oxygen in PS II of green plants.