Thermodynamic View of Proton Activated Electron Transfer in the Reaction Center of Photosynthetic Bacteria

The temperature dependence of the sequential coupling of proton transfer to the second interquinone electron transfer is studied in the reaction center proteins of photosynthetic bacteria modified by different mutations and treatment by divalent cations. The Eyring plots of kinetics were evaluated by the Marcus theory of electron and proton transfer. In mutants of electron transfer limitation (including the wild type), the observed thermodynamic parameters had to be corrected for those of the fast proton pre-equilibrium. The electron transfer is nonadiabatic with transmission coefficient 6 X 10(-4), and the reorganization energy amounts to 1.2 eV. If the proton transfer is the rate limiting step, the reorganization energy and the works terms fall in the range of 200-500 meV, depending on the site of damage in the proton transfer chain. The product term is 100-150 meV larger than the reactant term. While the electron transfer mutants have a low free energy of activation (similar to 200 meV), the proton transfer variants show significantly elevated levels of the free energy barrier (similar to 500 meV). The second electron transfer in the bacterial reaction center can serve as a model system of coupled electron and proton transfer in other proteins or ion channels

Unstable semiquinone in photosynthetic reaction center

Ubiquinone can take up two electrons and two protons upon reduction and serves as essential redox cofactor in several proteins. Out of its 9 possible redox states, only Q and Q– are seen in the QA site and Q, Q– and QH2 in the Q8 site of the reaction center of photosynthetic bacterium Rhodobacter sphaeroides. The focus of our interest was the investigation of kinetic and energetic aspects of Q– stability in the Q8 binding site. Under physiological conditions, the semiquinone anion is very stable and it binds more tightly than Q or QH2. At high light intensity of continuous excitation, however, it binds poorly and favors release to the solution. We attribute the decrease of semiquinone affinity to conformational changes in the QB binding site upon repetitive and frequent charge separation (and subsequent very fast recombination) in the photochemically closed reaction center

Fluorescence induction reveals organization of antenna and reaction center in photosynthetic bacteria

The photochemical phase of the bacteriochlorophyll fluorescence induction generated by rectangular shape of laser diode illumination was measured in different organization levels {whole cell, chromatophore and isolated reaction center protein) of carotenoidtess mutant of purple photosynthetic bacterium Rhodobacter sphaeroides R-26.1. While the antenna containing species showed large and positive variable fluorescence (fj relative to the constant (initial) fluorescence (Fa) {FJF^ ~ 4.5 in whole ceil), the isolated RC had smaller and negative change (FJF - -0.6). The variable fluorescence of the ceils increased steadily in the function of the age of the cultivated bacterium: FJF0 - 2 for young ceils and FJF0 - 4.5 fór old ceils while the rise time of the fluorescence induction remained constant (- 2 ms). In chromatophore, 7 times higher rate was measured than in isolated reaction center under identical experimental conditions. The results obtained under different conditions are interpreted by an extended version of the Lavergne-Trissl model where the simultaneously measured fluorescence inductions from the antenna and the RC can be separately expressed

Characterization of Polymers Used by Additive Manufacturing Technologies in Development of Medical Equipment

Today additive manufacturing technologies (AM – Additive Manufacturing) are emerging in both fields of science and industry. Specifically, highly tuned 3D printing technologies can be found in common households, thanks to the rapid development of the technology and the remarkable corresponding IT solutions. Additive manufacturing bears a significant impact upon fundamental (e.g., material science) and applied areas of research (e.g., medical and clinical studies, industrial, mechanical and electrical applications). Most recent international studies have aptly demonstrated how 3D printing is the midst of an exploding, developmental era. The appearance of new materials and device manufacturing demands the scientific, critical evaluation of the technology, aligned with their practical implementation. Despite the prominence of additive manufacturing in the field of emerging technologies dating from the 1980’s, it has gained immense international attention in the past decade. On a global scale, several research groups worked towards a solution not to ‘remove’ (e.g., CNC – computer numerical control) the material from the initial object, but to ‘add’ to it, therefore the manufactured object is built up in numerous layers, reducing material loss, saving time and costs. The first successful patent was filed by Charles Hull in the United States in 1984 in support of the process defined as SLA (SLA – stereolitography apparatus), in which the material was liquid-state photopolymer and hardened through the use of UV light. The first commercially available 3D printers operated very much the same as in the case of the 3D Systems, model SLA-1, 1987. In 1989, SLA 3D printers first appeared in Japan (products of NTT Data CMET and Sony/DMEC) and shortly afterwards followed by the German business entity, EOS (EOS - Electro Optical Systems). Several years later, in 1991, three new technologies appeared on the market, the filament-based Fused Deposit Modelling (FDM™), the ‘solid-ground-curing’ (SGC, Cubital), which is similar to SLA and the ‘laminated-object-manufacturing’ (LOM, by Helisys), in which a laser cuts out the structure from layers positioned on the top of one another. The next important milestone was the appearance of SLS (SLS – selective laser sintering) in 1992, which was the proprietary of DTM, and currently known as 3D Systems. The polymer powder based technology initiated the development of DMLS (DMLS – Direct Metal Laser sintering by Fraunhofer Institute, ILT, from Germany), which used metal powders as its material source. Both technologies are deemed relevant in both industrial and medical applications. The widening dispersion regarding 3D printing technology burst onto the scene in the middle of the 1990s when several manufacturers lowered the retail price regarding 3D print consumer goods. A superb example was the model Z402 inkjet 3D printer, which was the product of Z. Corp, or the paper-based 3D printer, which originated from Schroff Development, and featured a retail cost under $10,000. Up through the middle of the 2000s retail costs underwent a consistent decrease making the new technology more affordable, and the trend was coupled with an increase in product solutions and development. Today 3D printers are available to the general public for a few hundred dollars and are marketed in the form of household use. These desktop devices are referred to as FFF (FFF – Fused Filament Fabrication), such as in the model RepRap. The fall in retail costs obviously served as an immense impact regarding professional use, particularly in the applications of medical research and industrial manufacturing. Thanks to the academic and market-based start-up business entities, not only did FFF, DLP and SLA solutions undergo a substantial drop in retail costs, the availability of industrial scale devices soared

Stoichiometry and kinetics of mercury uptake by photosynthetic bacteria

Mercury adsorption on the cell surface and intracellular uptake by bacteria represent the key first step in the production and accumulation of highly toxic mercury in living organisms. In this work, the biophysical characteristics of mercury bioaccumulation are studied in intact cells of photosynthetic bacteria by use of analytical (dithizone) assay and physiological photosynthetic markers (pigment content, fluorescence induction, and membrane potential) to determine the amount of mercury ions bound to the cell surface and taken up by the cell. It is shown that the Hg(II) uptake mechanism (1) has two kinetically distinguishable components, (2) includes co-opted influx through heavy metal transporters since the slow component is inhibited by Ca2+ channel blockers, (3) shows complex pH dependence demonstrating the competition of ligand binding of Hg(II) ions with H+ ions (low pH) and high tendency of complex formation of Hg(II) with hydroxyl ions (high pH), and (4) is not a passive but an energy-dependent process as evidenced by light activation and inhibition by protonophore. Photosynthetic bacteria can accumulate Hg(II) in amounts much (about 105) greater than their own masses by well-defined strong and weak binding sites with equilibrium binding constants in the range of 1 (muM)-1 and 1 (mM)-1, respectively. The strong binding sites are attributed to sulfhydryl groups as the uptake is blocked by use of sulfhydryl modifying agents and their number is much (two orders of magnitude) smaller than the number of weak binding sites. Biofilms developed by some bacteria (e.g., Rvx. gelatinosus) increase the mercury binding capacity further by a factor of about five. Photosynthetic bacteria in the light act as a sponge of Hg(II) and can be potentially used for biomonitoring and bioremediation of mercury-contaminated aqueous cultures