Temperature dependence of P680+ reduction in O2-evolving PS II membrane fragments at different redox states Si of the water oxidizing system

AbstractThe electron transfer kinetics from Z to P680+ was analyzed as a function of temperature in the range of 248<T< 295 K by measuring absorption changes induced at 830 nm by a laser flash train in dark adapted O2 evolving PS II membrane fragments from spinach. It was found: (i) that the kinetics of P680+ reduction and their dependence on the redox state Si of the catalytic site of water oxidation are only slightly affected by temperature within the physiological range of 270<T<295 K. (ii) In the dark relaxed state S, the electron transfer from Z to P680+ exhibits an activation energy of the order of 10 kJ/mol in 248<T<295 K. (iii) In the 2nd and subsequent flashes of the train the ability for a stable charge separation between P680+ and Q−A, markedly decreases below −10°C. This phenomenon is assumed to be due to a strong effect of temperature on the electron transfer from Q−A to QB. The results are briefly discussed in relation to possible effects of structural changes in the D-1/D-2 polypeptide complex on the reaction coordinate of electron transfer steps in PS II

From large deviations to Wasserstein gradient flows in multiple dimensions

We study the large deviation rate functional for the empirical distribution of independent Brownian particles with drift. In one dimension, it has been shown by Adams, Dirr, Peletier and Zimmer that this functional is asymptotically equivalent (in the sense of $\Gamma$-convergence) to the Jordan-Kinderlehrer-Otto functional arising in the Wasserstein gradient flow structure of the Fokker-Planck equation. In higher dimensions, part of this statement (the lower bound) has been recently proved by Duong, Laschos and Renger, but the upper bound remained open, since the proof of Duong et al relies on regularity properties of optimal transport maps that are restricted to one dimension. In this note we present a new proof of the upper bound, thereby generalising the result of Adams et al to arbitrary dimensions

Herbicide/Quinone Binding Interactions in Photosystem II

Many inhibitors prevent the oxidation of the primary electron-accepting quinone (QA) by the secondary quinone (Qв) in photosystem II by displacement of Qв from its binding site. On the other hand, plastoquinone-1 and 6-azido-5-decyl-2,3-dim ethoxy-p-benzoquinone displace herbicides. Binding studies show the herbicide/quinone interaction to be (apparently) competitive.The herbicide binding is influenced differentially by various treatments. In this paper it is shown that the affinity of, for example, bromoxynil is decreased by thylakoid unstacking or by light-or reductant-induced reduction of certain thylakoid components, whereas atrazine affinity remains unchanged. Furthermore, absence of HCO-3 in the presence of form ate leads to an affinity decrease of bromoxynil and atrazine, but to an increase in i-dinoseb affinity. Other differential photosystem II herbicide effects are known from the literature.Since different and unrelated groups of Q-A oxidation inhibitors have been found, and because of the above-mentioned dissimilarities in binding characteristics for different inhibitor groups, the hypothesis of non-identical, but “overlapping” binding sites for different herbicide groups and the native quinone must be more extensively defined. In this manuscript we evaluate both the competitive herbicide/quinone binding model, and a model in which binding of one ligand alters the protein conformation resulting in a dramatic decrease in the binding affinity of ligands from other chemical groups; in this model ligands from the same or related chemical groups bind competitively. Thus, the latter model proposes that only one herbicide or quinone molecule can be bound with high affinity to the herbicide/quinone binding environment, but it depends on the chemical structure of the ligands whether the binding interaction between two ligands is truly competitive or more indirect (allosteric), mediated through the protein conformation

A Developmental Switch in Neurotransmitter Flux Enhances Synaptic Efficacy by Affecting AMPA Receptor Activation

AbstractFormation of glutamatergic synapses entails development of “silent” immature contacts into mature functional synapses. To determine how this transformation occurs, we investigated the development of neurotransmission at single synapses in vitro. Maturation of presynaptic function, assayed with endocytotic markers, followed accumulation of synapsin I. During this period, synaptic transmission was primarily mediated by activation of NMDA receptors, suggesting that most synapses were functionally silent. However, local glutamate application to silent synapses indicated that these synapses contained functional AMPA receptors, suggesting a possible presynaptic locus for silent transmission. Interference with presynaptic vesicle fusion by exposure to tetanus toxin reverted functional to silent transmission, implicating SNARE-mediated fusion as a determinant of the ratio of NMDA:AMPA receptor activation. This work reveals that functional maturation of synaptic transmission involves transformation of presynaptic silent secretion into mature synaptic transmitter release

Molecular evidence for increased regulatory conservation during metamorphosis, and against deleterious cascading effects of hybrid breakdown in Drosophila

<p>Abstract</p> <p>Background</p> <p>Speculation regarding the importance of changes in gene regulation in determining major phylogenetic patterns continues to accrue, despite a lack of broad-scale comparative studies examining how patterns of gene expression vary during development. Comparative transcriptional profiling of adult interspecific hybrids and their parental species has uncovered widespread divergence of the mechanisms controlling gene regulation, revealing incompatibilities that are masked in comparisons between the pure species. However, this has prompted the suggestion that misexpression in adult hybrids results from the downstream cascading effects of a subset of genes improperly regulated in early development.</p> <p>Results</p> <p>We sought to determine how gene expression diverges over development, as well as test the cascade hypothesis, by profiling expression in males of <it>Drosophila melanogaster</it>, <it>D. sechellia</it>, and <it>D. simulans</it>, as well as the <it>D. simulans </it>(♀) × <it>D. sechellia </it>(♂) male F1 hybrids, at four different developmental time points (3rd instar larval, early pupal, late pupal, and newly-emerged adult). Contrary to the cascade model of misexpression, we find that there is considerable stage-specific autonomy of regulatory breakdown in hybrids, with the larval and adult stages showing significantly more hybrid misexpression as compared to the pupal stage. However, comparisons between pure species indicate that genes expressed during earlier stages of development tend to be more conserved in terms of their level of expression than those expressed during later stages, suggesting that while Von Baer's famous law applies at both the level of nucleotide sequence and expression, it may not apply necessarily to the underlying overall regulatory network, which appears to diverge over the course of ontogeny and which can only be ascertained by combining divergent genomes in species hybrids.</p> <p>Conclusion</p> <p>Our results suggest that complex integration of regulatory circuits during morphogenesis may lead to it being more refractory to divergence of underlying gene regulatory mechanisms - more than that suggested by the conservation of gene expression levels between species during earlier stages. This provides support for a 'developmental hourglass' model of divergence of gene expression in <it>Drosophila </it>resulting in a highly conserved pupal stage.</p

Untersuchungen zur optimalen Eisenversorgung bei ökologisch gehaltenen Saugferkeln

During their suckling period, piglets´ demand for the essential trace element iron cannot be satisfied by sows´ milk alone. Because modern farrowing systems prevent piglets from rooting in soil to ensure additional iron intake, both conventional and organic farmers supplement iron by injection on day 3 post natum (p.n.). However, it is questionable if a single iron injection is sufficient for organic piglets, whose suckling period is 2-3 weeks longer than for their conventional counterparts. Therefore, this study compared a single iron injection on day 3 p.n. (E1) with two injections on day 3 and 14 (E2), and three injections on day 3, 14 and 21 (E3). The significantly lowest blood hematocrit levels and daily weight gains until weaning were found in E1 piglets, allowing the conclusion that a second iron injection is recommendable

Analysis of the electron transfer from Pheo− to QA in PS II membrane fragments from spinach by time resolved 325 nm absorption changes in the picosecond domain

AbstractAbsorption changes at 325 nm (ΔA325) induced by 15 ps laser flashes (λ = 650 nm) in PS II membrane fragments were measured with picosecond time-resolution. In samples with the reaction centers (RCs) kept in the open state (P I QA) the signals are characterized by a very fast rise (not resolvable by our equipment) followed by only small changes within our time window of 1.6 ns. In the closed state (P I Q−A) of the reaction center the signal decays with an average half-life time of about 250 ps. It is shown that under our excitation conditions (E = 2 × 1014 photons/cm2 per pulse) subtraction of the absorption changes in closed RCs (ΔAclosed325) from those in open RCs (ΔAopen325) leads to a difference signal which is dominated by the reduction kinetics of QA. From the rise kinetics of this signal and by comparison with data in the literature it is inferred that QA becomes reduced by direct electron transfer from Pheo− with a time constant of about 350 ± 100 ps

Polymers in Curved Boxes

We apply results derived in other contexts for the spectrum of the Laplace operator in curved geometries to the study of an ideal polymer chain confined to a spherical annulus in arbitrary space dimension D and conclude that the free energy compared to its value for an uncurved box of the same thickness and volume, is lower when $D < 3$, stays the same when $D = 3$, and is higher when \mbox{$D > 3$}. Thus confining an ideal polymer chain to a cylindrical shell, lowers the effective bending elasticity of the walls, and might induce spontaneous symmetry breaking, i.e. bending. (Actually, the above mentioned results show that {\em {any}} shell in $D = 3$ induces this effect, except for a spherical shell). We compute the contribution of this effect to the bending rigidities in the Helfrich free energy expression.Comment: 20 pages RevTeX, epsf; 4 figures; submitted to Macromoledule

Vertical motion of the thermocline, nitracline and chlorophyll maximum layers in relation to currents on the Southern California Shelf

A continuous four-day time series of nitrate concentration, temperature, chlorophyll fluorescence, and currents, sampled at fixed depths, revealed that distributions of temperature and nitrate could be accounted for by vertical motions in the water column associated with the semidiurnal internal tide and internal waves. A probable mixing event was observed: the transport of nitrate into the surface-layer associated with shear instabilities generated by internal waves. On temporal scales of less than a few hours, the variation of chlorophyll fluorescence could also be explained by vertical advection. However, on longer scales, swimming behavior of the phytoplankton assemblage (dominated by Ceratium spp.), along with vertical motions in the water column, appears to account for the vertical distribution of chlorophyll. These results indicate that the nitracline maintains a stable relationship with the density structure of the water column on a scale of days, whereas the subsurface chlorophyll maximum can change significantly over several hours

Isolation and properties of PS II membrane fragments depleted of the non heme iron center

AbstractThe functional properties and the content of non heme iron and cytochrome b559 were investigated by measuring flash induced transient changes of the relative fluorescence quantum yield and applying Mössbauer spectroscopy. It was found that untreated PS II membrane fragments contain a heterogeneous population of two types of non heme iron centers and about 2 cytochrome b559 per PS II. Twofold treatment of these samples with a recently described ‘iron depletion’ procedure (MacMillan, F., Lendzian, F., Renger, G. and Lubitz, W. (1995) Biochemistry 34, 3144–8156) leads to a complete loss (below the detection limit of Mössbauer spectroscopy) of the non heme iron center while more than 50% of the PS II complexes retain the functional integrity for light induced formation of the ‘stable’ radical pair YZOX P680Pheo QA−.. This sample type deprived of virtually all non heme iron in PS II provides a most suitable material for magnetic resonance studies that require an elimination of the interaction between Fe2+ and nearby radicals