hydrogen evolution reaction
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The synergetic effect of hydrophilic and hydrophobic carbon can be used to obtain tunable hydrogen evolution reaction (HER) at the interface. Herein, graphene oxide (GO-Hummers method) was coated on graphene foam (GF) synthesized via chemical vapor deposition to develop mixed-dimensional heterostructure for the observation of HER. The porosity of GF not only provides an optimized diffusion coefficient for better mass transport but also modified surface chemistry (GF/GO-hydrophobic/hydrophilic interface), which results in an onset potential 50 mV and overpotential of 450 mV to achieve the current density 10 mA/cm2. The surface analysis shows that inherent functional groups at the surface played a key role in tuning the activity of hybrid, providing a pathway to introduce non-corrosive electrodes for water splitting.
Previously, it has been shown that proteins and some polysaccharides (PSs) catalyse hydrogen evolution, producing electrochemical signals on mercury electrodes. The catalytic hydrogen evolution reaction (CHER) of the above-mentioned biomacromolecules was studied by voltammetric and chronopotentiometric stripping (CPS) methods. To obtain more information about electrode processes involving CHER, here we used protein such as BSA, and chitosan as a PS; in addition, we investigated dextran as a control PS not involved in CHER. We studied biomacromolecules by phase-sensitive alternating current (AC) voltammetry. Using phase-in AC voltammetry, for CHER-involved biomacromolecules we observed a CHER peak at highly negative potentials, similar to that observed with other voltammetric and CPS methods. On the other hand, by means of the adsorption/desorption processes studied in phase-out AC voltammetry, we uncovered a sharp and narrow decrease of capacitive current in the potential range of the CHER peak, denominated as the tensammetric minimum. This minimum was closely related to the CHER peak, as demonstrated by similar dependences on specific conditions affecting the CHER peak such as buffer capacity and pH. A tensammetric minimum was not observed for dextran. Our results suggest specific organization of biopolymer layers at negative potentials observed only in biomacromolecules involved in CHER.
- MeSH
- adsorpce MeSH
- chitosan chemie MeSH
- dextrany chemie MeSH
- elektrody MeSH
- Helix (hlemýždi) chemie MeSH
- katalýza MeSH
- konduktometrie přístrojové vybavení MeSH
- konkanavalin A chemie MeSH
- rtuť MeSH
- sérový albumin hovězí chemie MeSH
- skot MeSH
- vodík chemie MeSH
- zvířata MeSH
- Check Tag
- skot MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
The PsbO protein is an essential extrinsic subunit of photosystem II, the pigment-protein complex responsible for light-driven water splitting. Water oxidation in photosystem II supplies electrons to the photosynthetic electron transfer chain and is accompanied by proton release and oxygen evolution. While the electron transfer steps in this process are well defined and characterized, the driving forces acting on the liberated protons, their dynamics and their destiny are all largely unknown. It was suggested that PsbO undergoes proton-induced conformational changes and forms hydrogen bond networks that ensure prompt proton removal from the catalytic site of water oxidation, i.e. the Mn4 CaO5 cluster. This work reports the purification and characterization of heterologously expressed PsbO from green algae Chlamydomonas reinhardtii and two isoforms from the higher plant Solanum tuberosum (PsbO1 and PsbO2). A comparison to the spinach PsbO reveals striking similarities in intrinsic protein fluorescence and CD spectra, reflecting the near-identical secondary structure of the proteins from algae and higher plants. Titration experiments using the hydrophobic fluorescence probe ANS revealed that eukaryotic PsbO proteins exhibit acid-base hysteresis. This hysteresis is a dynamic effect accompanied by changes in the accessibility of the protein's hydrophobic core and is not due to reversible oligomerization or unfolding of the PsbO protein. These results confirm the hypothesis that pH-dependent dynamic behavior at physiological pH ranges is a common feature of PsbO proteins and causes reversible opening and closing of their β-barrel domain in response to the fluctuating acidity of the thylakoid lumen.
The monomeric photosystem I-light-harvesting antenna complex I (PSI-LHCI) supercomplex from the extremophilic red alga Cyanidioschyzon merolae represents an intermediate evolutionary link between the cyanobacterial PSI reaction center and its green algal/higher plant counterpart. We show that the C. merolae PSI-LHCI supercomplex is characterized by robustness in various extreme conditions. By a combination of biochemical, spectroscopic, mass spectrometry, and electron microscopy/single particle analyses, we dissected three molecular mechanisms underlying the inherent robustness of the C. merolae PSI-LHCI supercomplex: (1) the accumulation of photoprotective zeaxanthin in the LHCI antenna and the PSI reaction center; (2) structural remodeling of the LHCI antenna and adjustment of the effective absorption cross section; and (3) dynamic readjustment of the stoichiometry of the two PSI-LHCI isomers and changes in the oligomeric state of the PSI-LHCI supercomplex, accompanied by dissociation of the PsaK core subunit. We show that the largest low light-treated C. merolae PSI-LHCI supercomplex can bind up to eight Lhcr antenna subunits, which are organized as two rows on the PsaF/PsaJ side of the core complex. Under our experimental conditions, we found no evidence of functional coupling of the phycobilisomes with the PSI-LHCI supercomplex purified from various light conditions, suggesting that the putative association of this antenna with the PSI supercomplex is absent or may be lost during the purification procedure.
- MeSH
- biologická adaptace MeSH
- chlorofyl metabolismus MeSH
- cirkulární dichroismus MeSH
- fluorescenční spektrometrie MeSH
- fotosystém I (proteinový komplex) chemie metabolismus MeSH
- koncentrace vodíkových iontů MeSH
- molekulární evoluce MeSH
- Rhodophyta chemie fyziologie MeSH
- sinice chemie fyziologie MeSH
- světlo MeSH
- světlosběrné proteinové komplexy chemie metabolismus MeSH
- teplota MeSH
- zeaxanthiny metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Chronopotenciometrická rozpouštěcí analýza s konstantním proudem (CPS) je vysoce citlivá metoda analýzy proteinů, která nevyžaduje úpravu ve formě modifikace či značení. Během CPS analýzy poskytují proteiny tzv. pík H, který vzniká v důsledku katalytické reakce vylučování vodíku. Tento pík je citlivý na lokální i globální změny v proteinové struktuře a umožňuje zkoumání jak samostatných proteinů, tak i jejich komplexů. CPS analýza proteinů našla své uplatnění při studování biomedicínsky důležitých proteinů, které hrají roli například v průběhu neurodegenerativních onemocnění nebo rakoviny. V tomto článku popisujeme vývoj CPS analýzy proteinů a její pokrok za poslední desetiletí. Ukazujeme také všestrannost metody a potenciál jejího využití.
Chronopotentiometric constant current stripping analysis (CPS) is a highly sensitive method for protein analysis that does not require modification or labeling. During the CPS analysis, proteins yield the so-called peak H, resulting from the catalytic hydrogen evolution reaction. This peak is sensitive to both local and global changes in protein structure, allowing the study of individual proteins, as well as their complexes. CPS analysis has been utilized in studying biomedically important proteins involved in neurodegenerative diseases and cancer. In this article, we describe the development of CPS protein analysis and its progress over the past decade. We also demonstrate the versatility of the method and its potential applications.
- MeSH
- elektrochemie * metody MeSH
- lidé MeSH
- potenciometrie * metody MeSH
- proteiny * analýza chemie MeSH
- vazba proteinů MeSH
- vodík analýza chemie MeSH
- Check Tag
- lidé MeSH
We report that 3',5'-cyclic CMP undergoes nonenzymatic di- and trimerization at 20 °C under dry conditions upon proton or UV irradiation. The reaction involves stacking of the cyclic monomers and subsequent polymerization through serial transphosphorylations between the stacked monomers. Proton- and UV-induced oligomerization of 3',5'-cyclic CMP demonstrates that pyrimidines-similar to purines-might also have taken part in the spontaneous generation of RNA under plausible prebiotic conditions as well as in an extraterrestrial context. The observed polymerization of naturally occurring 3',5'-cyclic nucleotides supports the possibility that the extant genetic nucleic acids might have originated by way of a straight Occamian path, starting from simple reactions between plausibly preactivated monomers.
- MeSH
- chemické modely MeSH
- cirkulární dichroismus MeSH
- CMP cyklický chemie účinky záření MeSH
- evoluce chemická MeSH
- oligoribonukleotidy chemická syntéza MeSH
- polymerizace MeSH
- protony MeSH
- RNA chemická syntéza MeSH
- spektrometrie hmotnostní - ionizace laserem za účasti matrice MeSH
- ultrafialové záření MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Compartmentalization was likely essential for primitive chemical systems during the emergence of life, both for preventing leakage of important components, i.e., genetic materials, and for enhancing chemical reactions. Although life as we know it uses lipid bilayer-based compartments, the diversity of prebiotic chemistry may have enabled primitive living systems to start from other types of boundary systems. Here, we demonstrate membraneless compartmentalization based on prebiotically available organic compounds, α-hydroxy acids (αHAs), which are generally coproduced along with α-amino acids in prebiotic settings. Facile polymerization of αHAs provides a model pathway for the assembly of combinatorially diverse primitive compartments on early Earth. We characterized membraneless microdroplets generated from homo- and heteropolyesters synthesized from drying solutions of αHAs endowed with various side chains. These compartments can preferentially and differentially segregate and compartmentalize fluorescent dyes and fluorescently tagged RNA, providing readily available compartments that could have facilitated chemical evolution by protecting, exchanging, and encapsulating primitive components. Protein function within and RNA function in the presence of certain droplets is also preserved, suggesting the potential relevance of such droplets to various origins of life models. As a lipid amphiphile can also assemble around certain droplets, this further shows the droplets' potential compatibility with and scaffolding ability for nascent biomolecular systems that could have coexisted in complex chemical systems. These model compartments could have been more accessible in a "messy" prebiotic environment, enabling the localization of a variety of protometabolic and replication processes that could be subjected to further chemical evolution before the advent of the Last Universal Common Ancestor.
- MeSH
- fluorescenční barviva chemie MeSH
- FRAP MeSH
- koncentrace vodíkových iontů MeSH
- kyseliny karboxylové chemie MeSH
- membrány umělé * MeSH
- polyestery chemická syntéza chemie MeSH
- původ života * MeSH
- RNA chemie MeSH
- velikost částic MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
BACKGROUND: With limited agricultural land and increasing human population, it is essential to enhance overall photosynthesis and thus productivity. Oxygenic photosynthesis begins with light absorption, followed by excitation energy transfer to the reaction centres, primary photochemistry, electron and proton transport, NADPH and ATP synthesis, and then CO2 fixation (Calvin-Benson cycle, as well as Hatch-Slack cycle). Here we cover some of the discoveries related to this process, such as the existence of two light reactions and two photosystems connected by an electron transport 'chain' (the Z-scheme), chemiosmotic hypothesis for ATP synthesis, water oxidation clock for oxygen evolution, steps for carbon fixation, and finally the diverse mechanisms of regulatory processes, such as 'state transitions' and 'non-photochemical quenching' of the excited state of chlorophyll a. SCOPE: In this review, we emphasize that mathematical modelling is a highly valuable tool in understanding and making predictions regarding photosynthesis. Different mathematical models have been used to examine current theories on diverse photosynthetic processes; these have been validated through simulation(s) of available experimental data, such as chlorophyll a fluorescence induction, measured with fluorometers using continuous (or modulated) exciting light, and absorbance changes at 820 nm (ΔA820) related to redox changes in P700, the reaction centre of photosystem I. CONCLUSIONS: We highlight here the important role of modelling in deciphering and untangling complex photosynthesis processes taking place simultaneously, as well as in predicting possible ways to obtain higher biomass and productivity in plants, algae and cyanobacteria.
- MeSH
- biomasa MeSH
- chlorofyl a * MeSH
- chlorofyl MeSH
- fotosyntéza * MeSH
- fotosystém II (proteinový komplex) MeSH
- kyslík MeSH
- lidé MeSH
- světlo MeSH
- transport elektronů MeSH
- voda MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
The unicellular cyanobacterium Cyanothece sp. American Type Culture Collection (ATCC) 51142 is capable of performing oxygenic photosynthesis during the day and microoxic nitrogen fixation at night. These mutually exclusive processes are possible only by temporal separation by circadian clock or another cellular program. We report identification of a temperature-dependent ultradian metabolic rhythm that controls the alternating oxygenic and microoxic processes of Cyanothece sp. ATCC 51142 under continuous high irradiance and in high CO2 concentration. During the oxygenic photosynthesis phase, nitrate deficiency limited protein synthesis and CO2 assimilation was directed toward glycogen synthesis. The carbohydrate accumulation reduced overexcitation of the photosynthetic reactions until a respiration burst initiated a transition to microoxic N2 fixation. In contrast to the circadian clock, this ultradian period is strongly temperature-dependent: 17 h at 27 °C, which continuously decreased to 10 h at 39 °C. The cycle was expressed by an oscillatory modulation of net O2 evolution, CO2 uptake, pH, fluorescence emission, glycogen content, cell division, and culture optical density. The corresponding ultradian modulation was also observed in the transcription of nitrogenase-related nifB and nifH genes and in nitrogenase activities. We propose that the control by the newly identified metabolic cycle adds another rhythmic component to the circadian clock that reflects the true metabolic state depending on the actual temperature, irradiance, and CO2 availability.
- MeSH
- bakteriální proteiny genetika metabolismus MeSH
- bioreaktory mikrobiologie MeSH
- cirkadiánní rytmus genetika fyziologie MeSH
- Cyanothece genetika růst a vývoj metabolismus MeSH
- fixace dusíku genetika fyziologie MeSH
- fotosyntéza genetika fyziologie MeSH
- glykogen metabolismus MeSH
- koncentrace vodíkových iontů MeSH
- kyslík metabolismus MeSH
- oxid uhličitý metabolismus MeSH
- oxidoreduktasy genetika metabolismus MeSH
- polymerázová řetězová reakce s reverzní transkripcí MeSH
- regulace genové exprese u bakterií MeSH
- vývojová regulace genové exprese MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
... Contents -- PART 1 THE MOLECULAR DESIGN OF LIFE -- Chapter 1 Prelude 3 -- Chapter 2 Biochemical Evolution ... ... DNA, and the Flow of Genetic Information 117 -- Chapter 6 Exploring Genes 143 chapter 7 Exploring Evolution ... ... Chapter 19 -- Chapter 20 -- Chapter 21 Chapter 22 -- Oxidative Phosphorylation 491 -- The Light Reactions ... ... of Evolution Can Be Demonstrated in Vitro 22 -- 2.2.2 RNA Molecules Can Act Äs Catalysts 23 -- 2.2.3 ... ... 194 -- 8.2.3 Enzymes Alter Only the Reaction Rate and Not the Reaction Equilibrium 19 6 -- 8.3 Enzymes ...
5th ed. xvii, 974 s. : il., tab., grafy ; 32 cm
