Species-dependent alteration of electron transfer in the early stages of charge stabilization in Photosystem I.

Electron transfer (ET) in Photosystem I (PS I) is bidirectional, occurring in two pseudosymmetric branches of cofactors. The relative use of two branches in the green alga Chlamydomonas reinhardtii and the cyanobacterium Synechocystis sp. PCC 6803 has been studied by changing the Met axial ligands of the chlorophyll a acceptor molecules, A0A and A0B, to His. The nature of the effect on the ET is found to be species dependent. In C. reinhardtii, transient absorption and transient EPR data show that in the M688HPsaA variant, forward ET from A0A to the quinone, A1A, is blocked in 100% of the PS I complexes. In contrast, in Synechocystis sp. PCC 6803, forward ET from A0A to A1A is blocked in only 50% of the PS I complexes, but in those PS I complexes in which electrons reach A1A, further transfer to the iron-sulfur cluster FX is blocked. Similar species differences are found for the corresponding B-branch variants. One possible explanation of this behavior is that it is the result of two conformers in which an H-bond between the His side chain and the O1 carbonyl group of A1 is either present or absent. The spectroscopic data suggest that the two conformers are present in nearly equal amounts in the Synechocystis sp. PCC 6803 variants, while only the conformer without the H-bond is present in the same variants of C. reinhardtii.

Alcohol industry and non-alcohol industry sponsorship of sportspeople and drinking.

AIMS: To examine the relationship between direct alcohol and non-alcohol sponsorship and drinking in Australian sportspeople. METHODS: Australian sportspeople (N = 652; 51% female) completed questionnaires on alcohol and non-alcohol industry sponsorship (from bars, cafes etc.), drinking behaviour (Alcohol Use Disorders Identification Test (AUDIT)) and known confounders. RESULTS: 31% reported sponsorship (29.8% alcohol industry; 3.7% both alcohol and non-alcohol industry and 1.5% non-alcohol industry only) Multivariate regression showed that receipt of alcohol industry sponsorship was predictive of higher AUDIT scores (ß(adj) = 1.67, 95% confidence interval (CI): 0.56-2.78), but non-alcohol industry sponsorship and combinations of both were not (ß(adj) = 0.18, 95% CI: -2.61 to 2.68; and ß(adj) = 2.58, 95% CI: -0.60 to 5.76, respectively). CONCLUSION: Governments should consider alternatives to alcohol industry sponsorship of sport. Hypothecated taxes on tobacco have been used successfully for replacing tobacco sponsorship of sport in some countries, and may show equal utility for the alcohol industry's funding of sport.

A simple method for chloroplast transformation in Chlamydomonas reinhardtii.

Photosystem I (PSI) is a multisubunit pigment-protein complex that uses light energy to transfer electrons from plastocyanin to ferredoxin. Application of genetic engineering to photosynthetic reaction center proteins has led to a significant advancement in our understanding of primary electron transfer events and the role of the protein environment in modulating these processes. Chlamydomonas reinhardtii provides a system particularly amenable to analyze the structure-function relationship of Photosystem I. C. reinhardtii is also a particularly favorable organism for chloroplast transformation because it contains only a single chloroplast and grows heterotrophically when supplemented with acetate. Chlamydomonas has, therefore, served as a model organism for the development of chloroplast transformation procedures and the study of photosynthetic mutants generated using this method. Exogenous cloned cpDNA can be introduced into the chloroplast by using this biolistic gene gun method. DNA-coated tungsten or gold particles are bombarded onto cells. Upon its entry into chloroplasts, the transforming DNA is released from the particles and integrated into the chloroplast genome through homologous recombination. The most versatile chloroplast selectable marker is aminoglycoside adenyl transferase (aadA), which can be expressed in the chloroplast to confer resistance to spectinomycin or streptomycin. This article describes the procedures for chloroplast transformation.

Alcohol consumption in sport: The influence of sporting idols, friends and normative drinking practices.

INTRODUCTION AND AIMS: High-profile sportspeople are posited as role models for others. We examine whether university sportspeople and non-sportspeople's perceptions of high-profile sportspeople's (sports stars) and friends perceived drinking behaviours are related to their own drinking behaviours. Further, we examine the importance of drinking with competitors after sports events. DESIGN AND METHODS: A convenience sample of 1028 participants (58% females, n=652 sportspeople) from two Australian universities were approached at sporting and university venues. Participants completed a survey booklet containing demographic questions, the Alcohol Use Disorders Identification Test (AUDIT, alcohol measure), perceived drinking of high-profile sportspeople and friends (social norms), and for sportspeople only, items assessing the importance of drinking with competitors. Bivariate and multivariate analyses were used to assess relationships. RESULTS: Both sporting and non-sporting participants perceived high-profile sportspeople to drink less than themselves and their friends. Small significant bivariate relationships were found between high-profile sportspeople's perceived drinking and self-reported drinking for sportspeople (r=0.20, P <0.0005). However, in multivariate regression models the perceived drinking behaviours of high-profile sportspeople were not significant predictors of sportspeople's drinking, and were negatively related to non-sportspeople's drinking. The practice of drinking with competitors after sports and games accounted for an additional 6.1% of the unique variance in AUDIT-scores (P<0.0005). DISCUSSION AND CONCLUSIONS: Sports stars are touted as negative role models when it comes to drinking. Contrary to expectations high-profile sportspeople were not perceived to be heavy drinkers and their perceived drinking was not predictive of others drinking. Friends' and normative drinking practices were predictors of drinking.[O'Brien KS, Kolt GS, Webber A, Hunter JA. Alcohol consumption in sport: The influence of sporting idols, friends and normative drinking practices.

Improving population health: the business community imperative.

Information on the economic effect of poor population health is needed to engage the business community in population health improvement. In a competitive global market, the United States has high health care costs and poor outcomes (measured by such factors as healthy and productive lives) compared with other countries. US business needs to understand population health and not focus just on the health of employees at the worksite. We describe a long-term approach to population health, including incentives, and identify what is needed to engage business leadership in population health improvement.

Structural and functional changes of PSI-LHCI supercomplexes of Chlamydomonas reinhardtii cells grown under high salt conditions.

The eVect of high salt concentration (100 mM NaCl) on the organization of photosystem I-light harvesting complex I supercomplexes (PSI-LHCI) of Chlamydomonas reinhardtii was studied. The electron transfer activity was reduced by 39% in isolated PSI-LHCI supercomplexes. The visible circular dichroism (CD) spectra associated with strongly coupled chlorophyll (Chl) dimers were reduced in intensity, indicating that pigment-pigment interactions were disrupted. This data is consistent with results from Xuorescence streak camera spectroscopy, which suggest that red-shifted pigments in the PSI-LHCI antenna had been lost. Denaturing gel electrophoresis and immunoblot analysis reveals that levels of the PSI reaction center proteins PsaD, PsaE and PsaF were reduced due to salt stress. PsaE is almost completely absent under high salt conditions. It is known that the membrane-extrinsic subunits PsaD and E form the ferredoxin-docking site. Our results indicate that the PSI-LHCI supercomplex is damaged by reactive oxygen species at high salt concentration, with particular impact on the ferredoxin-docking site and the PSILHCI interface.

Effect of the P700 pre-oxidation and point mutations near A(0) on the reversibility of the primary charge separation in Photosystem I from Chlamydomonas reinhardtii.

Time-resolved fluorescence studies with a 3-ps temporal resolution were performed in order to: (1) test the recent model of the reversible primary charge separation in Photosystem I (Müller et al., 2003; Holwzwarth et al., 2005, 2006), and (2) to reconcile this model with a mechanism of excitation energy quenching by closed Photosystem I (with P700 pre-oxidized to P700+). For these purposes, we performed experiments using Photosystem I core samples isolated from Chlamydomonas reinhardtii wild type, and two mutants in which the methionine axial ligand to primary electron acceptor, A(0), has been change to either histidine or serine. The temporal evolution of fluorescence spectra was recorded for each preparation under conditions where the "primary electron donor," P700, was either neutral or chemically pre-oxidized to P700+. For all the preparations under study, and under neutral and oxidizing conditions, we observed multiexponential fluorescence decay with the major phases of approximately 7 ps and approximately 25 ps. The relative amplitudes and, to a minor extent the lifetimes, of these two phases were modulated by the redox state of P700 and by the mutations near A(0): both pre-oxidation of P700 and mutations caused slight deceleration of the excited state decay. These results are consistent with a model in which P700 is not the primary electron donor, but rather a secondary electron donor, with the primary charge separation event occurring between the accessory chlorophyll, A, and A(0). We assign the faster phase to the equilibration process between the excited state of the antenna/reaction center ensemble and the primary radical pair, and the slower phase to the secondary electron transfer reaction. The pre-oxidation of P700 shifts the equilibrium between the excited state and the primary radical pair towards the excited state. This shift is proposed to be induced by the presence of the positive charge on P700+. The same charge is proposed to be responsible for the fast A+A(0)(-)-->AA(0) charge recombination to the ground state and, in consequence, excitation quenching in closed reaction centers. Mutations of the A(0) axial ligand shift the equilibrium in the same direction as pre-oxidation of P700 due to the up-shift of the free energy level of the state A+A(0)(-).

Electron transfer from A to A(1) in Photosystem I from Chlamydomonas reinhardtii occurs in both the A and B branch with 25-30-ps lifetime.

We have recorded transient absorption kinetics at 390 nm with picosecond resolution in order to observe electron transfer from the reduced primary acceptor, A, to the secondary acceptor, A(1), in wild type and mutated Photosystem I from Chlamydomonas reinhardtii. In the mutants, the methionine axial ligand to the primary electron acceptor in either the A- or B-branch of electron transfer cofactors, was replaced with histidine. Both of the mutations reduced the formation of a positive signal at 390 nm, characteristic of A to a level approximately half of that observed in wild type Photosystem I. It is concluded that in the mutated branch of Photosystem I, electron transfer from A to A(1) does not occur. The absorption kinetics resulting from subtraction of either of the mutants' traces from that of wild type is interpreted to reflect the kinetics of A- or B-side electron transfer from A to A(1) in the the wild type Photosystem I. Each of these traces could be fitted with a monoexpoenential decay characterized by the same amplitude and 25-30-ps lifetime. The almost identical effect of both mutations on A formation confirm a similar engagement of both the A- ad B-branches in electron transfer to A(1) in Photosystem I from C. reinhardtii. This observation is in contrast to the unidirectional electron transfer concluded from the studies on similar mutants of cyanobacterial Photosystem I.(1) Thus, this contribution provides further evidence for functional differences between these two model Photosystems.

Two equilibration pools of chlorophylls in the Photosystem I core antenna of Chlamydomonas reinhardtii.

Femtosecond transient absorption spectroscopy was applied for a comparative study of excitation decay in several different Photosystem I (PSI) core preparations from the green alga Chlamydomonas reinhardtii. For PSI cores with a fully interconnected network of chlorophylls, the excitation energy was equilibrated over a pool of chlorophylls absorbing at approximately 683 nm, independent of excitation wavelength [Gibasiewicz et al. J Phys Chem B 105:11498-11506, 2001; J Phys Chem B 106:6322-6330, 2002]. In preparations with impaired connectivity between chlorophylls, we have found that the spectrum of chlorophylls connected to the reaction center (i.e., with approximately 20 ps decay time) over which the excitation is equilibrated becomes excitation-wavelength-dependent. Excitation at 670 nm is finally equilibrated over chlorophylls absorbing at approximately 675 nm, whereas excitation at 695 nm or 700 nm is equilibrated over chlorophylls absorbing at approximately 683 nm. This indicates that in the vicinity of the reaction center there are two spectrally different and spatially separated pools of chlorophylls that are equally capable of effective excitation energy transfer to the reaction center. We propose that they are related to the two groups of central PSI core chlorophylls lying on the opposite sides of reaction center.

Quantitatively comparing morphological trends to environment in the fossil record (Cincinnatian series; Upper Ordovician).

Determining whether morphological trends in fossil species represent evolution within a lineage or lateral shifts in morphologically variable populations through time requires a thorough examination of the details of both morphology and paleoenvironment in time and space. The purpose of this study is to explore at high resolution the relationship between morphology of the trilobite Flexicalymene granulosa and paleoenvironmental conditions in Upper Ordovician deposits of southwestern Ohio and northern Kentucky. This is achieved by using geometric morphometrics to measure high-resolution morphological changes and by using gradient analysis to capture environmental gradients underlying faunal distribution patterns. Quantitatively comparing the outcomes of these two techniques provides an assessment of whether shape changes relates to environment. Results indicate that a significant amount of shape change, seen as an anteromedial movement of the eye region over time, corresponds to ordination scores. This suggests a relationship between certain aspects of morphology and environment. The combination of these quantitative techniques has provided the foundation for determining whether morphological trends within F. granulosa represent evolution or temporal shifts in geographic variation. Future work will involve examining this relationship in greater detail both geographically and stratigraphically.

Replacement of the methionine axial ligand to the primary electron acceptor A0 slows the A0- reoxidation dynamics in photosystem I.

The recent crystal structure of photosystem I (PSI) from Thermosynechococcus elongatus shows two nearly symmetric branches of electron transfer cofactors including the primary electron donor, P(700), and a sequence of electron acceptors, A, A(0) and A(1), bound to the PsaA and PsaB heterodimer. The central magnesium atoms of each of the putative primary electron acceptor chlorophylls, A(0), are unusually coordinated by the sulfur atom of methionine 688 of PsaA and 668 of PsaB, respectively. We [Ramesh et al. (2004a) Biochemistry 43:1369-1375] have shown that the replacement of either methionine with histidine in the PSI of the unicellular green alga Chlamydomonas reinhardtii resulted in accumulation of A(0)(-) (in 300-ps time scale), suggesting that both the PsaA and PsaB branches are active. This is in contrast to cyanobacterial PSI where studies with methionine-to-leucine mutants show that electron transfer occurs predominantly along the PsaA branch. In this contribution we report that the change of methionine to either leucine or serine leads to a similar accumulation of A(0)(-) on both the PsaA and the PsaB branch of PSI from C. reinhardtii, as we reported earlier for histidine mutants. More importantly, we further demonstrate that for all the mutants under study, accumulation of A(0)(-) is transient, and that reoxidation of A(0)(-) occurs within 1-2 ns, two orders of magnitude slower than in wild type PSI, most likely via slow electron transfer to A(1). This illustrates an indispensable role of methionine as an axial ligand to the primary acceptor A(0) in optimizing the rate of charge stabilization in PSI. A simple energetic model for this reaction is proposed. Our findings support the model of equivalent electron transfer along both cofactor branches in Photosystem I.