Net light-induced oxygen evolution in photosystem I deletion mutants of the cyanobacterium Synechocystis sp. PCC 6803.

Oxygenic photosynthesis in cyanobacteria, algae, and plants requires photosystem II (PSII) to extract electrons from H(2)O and depends on photosystem I (PSI) to reduce NADP(+). Here we demonstrate that mixotrophically-grown mutants of the cyanobacterium Synechocystis sp. PCC 6803 that lack PSI (ΔPSI) are capable of net light-induced O(2) evolution in vivo.

Kinetic imaging of chlorophyll fluorescence using modulated light.

Fluorometers that measure the kinetics of chlorophyll fluorescence have become invaluable tools for determining the photosynthetic performance of plants. Many of these instruments use high frequency modulated light to measure the rate, efficiency and regulation of photosynthesis. The technique is non-invasive and is effective under diverse environmental conditions.

Digital biology: an emerging and promising discipline.

This article examines the role of computation and quantitative methods in modern biomedical research to identify emerging scientific, technical, policy and organizational trends. It identifies common concerns and practices in the emerging community of computationally-oriented bio-scientists by reviewing a national symposium, Digital Biology: the Emerging Paradigm, held at the National Institutes of Health in Bethesda, Maryland, November 6th and 7th 2003. This meeting showed how biomedical computing promises scientific breakthroughs that will yield significant health benefits.

Cytochrome b6 arginine 214 of Synechococcus sp. PCC 7002, a key residue for quinone-reductase site function and turnover of the cytochrome bf complex.

Quinone-reductase (Q(i)) domains of cyanobacterial/chloroplast cytochrome bf and bacterial/mitochondrial bc complexes differ markedly, and the cytochrome bf Q(i) site mechanism remains largely enigmatic. To investigate the bf Q(i) domain, we constructed the mutation R214H, which substitutes histidine for a conserved arginine in the cytochrome b(6) polypeptide of the cyanobacterium Synechococcus sp. SPCC 7002.

The slow reversibility of photosystem II thermal energy dissipation on transfer from high to low light may cause large losses in carbon gain by crop canopies: a theoretical analysis.

Regulated thermal dissipation of absorbed light energy within the photosystem II antenna system helps protect photosystem II from damage in excess light. This reversible photoprotective process decreases the maximum quantum yield of photosystem II (Fv)/Fm) and CO2 assimilation (phiCO2), and decreases the convexity of the non-rectangular hyperbola describing the response of leaf CO2 assimilation to photon flux (theta). At high light, a decrease in phiCO2 has minimal impact on carbon gain, while high thermal energy dissipation protects PSII against oxidative damage.

Proteomic analysis of a highly active photosystem II preparation from the cyanobacterium Synechocystis sp. PCC 6803 reveals the presence of novel polypeptides.

A highly active oxygen-evolving photosystem II (PSII) complex was purified from the HT-3 strain of the widely used cyanobacterium Synechocystis sp. PCC 6803, in which the CP47 polypeptide has been genetically engineered to contain a polyhistidine tag at its carboxyl terminus [Bricker, T. M.

Modification of inhibitor binding sites in the cytochrome bf complex by directed mutagenesis of cytochrome b(6) in Synechococcus sp. PCC 7002.

The cytochrome bf complex, which links electron transfer from photosystem II to photosystem I in oxygenic photosynthesis, has not been amenable to site-directed mutagenesis in cyanobacteria. Using the cyanobacterium Synechococcus sp. PCC 7002, we have successfully modified the cytochrome b(6) subunit of the cytochrome bf complex.

Cytochrome cM from synechocystis 6803. Detection in cells, expression in Escherichia coli, purification and physical characterization.

Based on DNA sequence data a novel c-type cytochrome, cytochrome cM, has been predicted to exist in the cyanobacterium Synechocystis 6803. The precursor protein consists of 105 amino acids with a characteristic heme-binding motif and a hydrophobic domain located at the N-terminal end that is proposed to act as either a signal peptide or a membrane anchor. For the first time we report the detection of cytochrome cM in Synechocystis 6803 using Western blot analysis.

Extinction coefficients and midpoint potentials of cytochrome c(6) from the cyanobacteria Arthrospira maxima, Microcystis aeruginosa, and Synechocystis 6803.

Cytochrome c(6) is a soluble heme protein that serves as a photosynthetic electron transport component in cyanobacteria and algae, carrying electrons from the cytochrome bf complex to photosystem I. The rapid accumulation of cytochrome c(6) sequence data from a wide range of species, combined with significant advances in determining high resolution three-dimensional structures, provides a powerful database for investigating the relationship between structure and function. The fact that the gene encoding cytochrome c(6) can be readily modified in a number of species adds to the usefulness of cytochrome c(6) as a tool for comparative analysis.

Characterization of photosystem II activity and heterogeneity during the cell cycle of the green alga scenedesmus quadricauda.

The photosynthetic activity of the green alga Scenedesmus quadricauda was investigated during synchronous growth in light/dark cycles. The rate of O2 evolution increased 2-fold during the first 3 to 4 h of the light period, remained high for the next 3 to 4 h, and then declined during the last half of the light period. During cell division, which occurred at the beginning of the dark period, the ability of the cells to evolve O2 was at a minimum.

Structural model of cytochrome b559 in photosystem II based on a mutant with genetically fused subunits.

Photosystem II is a reaction center protein complex located in photosynthetic membranes of plants, algae, and cyanobacteria. Using light energy, photosystem II catalyzes the oxidation of water and the reduction of plastoquinone, resulting in the release of molecular oxygen. A key component of photosystem II is cytochrome b559, a membrane-embedded heme protein with an unknown function.

Critical analysis of the extinction coefficient of chloroplast cytochrome f.

In oxygenic photosynthesis the cytochrome bf complex links electron transport between photosystem II and photosystem I. The largest subunit of the complex is cytochrome f, a 32-kDa polypeptide that is anchored in the membrane by a transmembrane alpha helix located near the carboxyl end. The three-dimensional structure of the soluble domain of cytochrome f isolated from turnip has been determined by X-ray crystallography to 1.

School nurses' skills in sexual health education.

School nurses are often called on teach sexual health without being given any formal teacher training or support. This article describes a study of the experiences of 50 school nurses. The author suggests ways in which schools and their nurses could create supportive and complementary teaching partnerships for effective sex education.

Light-dependent modification of Photosystem II in spinach leaves.

In dark-adapted spinach leaves approximately one third of the Photosystem II (PS II) reaction centers are impaired in their ability to transfer electrons to Photosystem I. Although these 'inactive' PS II centers are capable of reducing the primary quinone acceptor, QA, oxidation of QA (-) occurs approximately 1000 times more slowly than at 'active' centers. Previous studies based on dark-adapted leaves show that minimal energy transfer occurs from inactive centers to active centers, indicating that the quantum yield of photosynthesis could be significantly impaired by the presence of inactive centers.

Active photosynthesis in cyanobacterial mutants with directed modifications in the ligands for two iron-sulfur clusters on the PsaC protein of photosystem I.

The PsaC protein of the Photosystem I (PSI) complex in thylakoid membranes coordinates two [4Fe-4S] clusters, FA and FB. Although it is known that PsaC participates in electron transfer to ferredoxin, the pathway of electrons through this protein is unknown. To elucidate the roles of FA and FB, we created two site-directed mutant strains of the cyanobacterium Anabaena variabilis ATCC 29413.

Site-directed mutagenesis of the CP 47 protein of photosystem II: alteration of conserved charged residues in the domain 364E-444R.

The intrinsic chlorophyll-protein CP 47 is a component of photosystem II in higher plants, green algae and cyanobacteria. We had shown previously by biochemical methods that the domain 364E-440D of CP 47 interacts with the 33 kDa extrinsic protein of photosystem II [Odom, W. R.

Evidence that cytochrome b559 protects photosystem II against photoinhibition.

Light that exceeds the photosynthetic capacity of a plant can impair the ability of photosystem II to oxidize water. The light-induced inhibition is initiated by inopportune electron transport reactions that create damaging redox states. There is evidence that secondary electron transport pathways within the photosystem II reaction center can protect against potentially damaging redox states.

Women and illicit drugs: sexuality and crack cocaine.

As part of a larger, federally funded study, the purpose of this preliminary, descriptive study was to describe the sexual feelings and sexual functioning of women who used large amounts of crack cocaine. A structured interview with questions pertaining to the effect of crack use on sexual feelings and sexual function was conducted with 100 African-American women who either were in treatment for crack abuse or were currently using the drug. The data did not support the commonly held notions that crack is an aphrodisiac for women and that crack makes women want sex.

African-American women who smoke crack cocaine: sexual trauma and the mother-daughter relationship.

This study evolved from previous writings that linked sexual abuse to the quality of the mother-daughter relationship. The purpose of this investigation was to examine the mother-daughter relationship among African-American women who abuse crack cocaine by comparing three different groups: women who have not experienced incest but have experienced sexual abuse; women who have experienced incest; and women who have not experienced sexual abuse. A convenience sample of 64 African-American women was used, 35 of whom were in drug abuse treatment and 29 of whom were abusing crack cocaine.

Photoautotrophic growth of the cyanobacterium Synechocystis sp. PCC 6803 in the absence of cytochrome c553 and plastocyanin.

In the cyanobacterium Synechocystis sp. PCC 6803, photosynthetic electron transport from the cytochrome bf complex to photosystem I can be mediated by cytochrome c553 or plastocyanin. The concentration of copper in the growth medium determines which protein is synthesized.

Functional size of Photosystem II determined by radiation inactivation.

The functional size of Photosystem II (PS II) was investigated by radiation inactivation. The technique provides an estimate of the functional mass required for a specific reaction and depends on irradiating samples with high energy γ-rays and assaying the remaining activity. The analysis is based on target theory that has been modified to take into account the temperature dependence of radiation inactivation of proteins.

Dissipation of the Proton Electrochemical Potential in Intact Chloroplasts (II. The pH Gradient Monitored by Cytochrome f Reduction Kinetics).

The potency of various uncouplers for collapsing the light-induced pH gradient across thylakoid membranes in intact chloroplasts was investigated by time-resolved optical spectroscopy. The thylakoid transmembrane pH gradient ([delta]pH) was monitored indirectly by measuring the rate of cytochrome (Cyt) f reduction following a light flash of sufficient duration to create a sizable [delta]pH. The results show that the rate of Cyt f reduction is controlled in part by the internal pH of the thylakoid inner aqueous space.

Copper-mediated regulation of cytochrome c553 and plastocyanin in the cyanobacterium Synechocystis 6803.

In certain cyanobacteria and algae, cytochrome c553 or plastocyanin can serve to carry electrons from the cytochrome bf complex to photosystem I. The availability of copper in the growth medium regulates which protein is present. To investigate copper induced control of gene expression we isolated these proteins from the cyanobacterium Synechocystis 6803.