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.

• MeSH
• elektrody MeSH
• grafit chemie   MeSH
• hydrofobní a hydrofilní interakce * MeSH
• katalýza MeSH
• poréznost MeSH
• uhlík chemie   MeSH
• voda chemie   MeSH
• vodík chemie   MeSH
• Publikační typ
• časopisecké články MeSH

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.

• MeSH
• Chlamydomonas reinhardtii metabolismus   MeSH
• fotosystém II (proteinový komplex) metabolismus   MeSH
• koncentrace vodíkových iontů MeSH
• Spinacia oleracea metabolismus   MeSH
• tylakoidy metabolismus   MeSH
• vodíková vazba MeSH
• Publikační typ
• časopisecké články MeSH

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

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

• MeSH
• biochemie MeSH

• Konspekt
• Biochemie. Molekulární biologie. Biofyzika
• NLK Obory
• biochemie

Although ganciclovir (gan) as a purine analogue is a compound of biological interest (antiviral drug), it has been rarely electrochemically studied. In this paper surface catalytic electrode mechanism based on the hydrogen evolution reaction is analyzed under conditions of square-wave voltammetry and differential capacity curves of double layer measurements. The electrode mechanism is assumed to involve a preceding chemical reaction in which the adsorbed catalyst (ganads) is protonated at the electrode surface, i.e., ganads + H+aq › ganH+ads. The protonated form of the catalyst (ganH+ads) is irreversibly reduced at potential about –1.35 V vs Ag|AgCl, yielding the initial form of the catalyst and atomic hydrogen, i.e., ganH+ads + e › ganads + Haq. Changes of zero charge potential and surface tension point to the adsorption of ganciclovir molecule directed with guanine group to the mercury surface and suggests that ganciclovir molecules are not placed flat on the mercury surface. The effect of adsorption on mercury electrode was studied in detail in respect to analytical usefulness of the obtained results. A new catalytic method for voltammetric determination of ganciclovir was developed. The detection and quantification limits were 1.3 × 10–7 and 4.3 × 10–7 mol l–1 for square-wave voltammetry, and 1.4 × 10–7 and 4.7 × 10–7 mol l–1 for linear-sweep voltammetry.

• MeSH
• antivirové látky analýza   chemie   MeSH
• elektrochemie metody   MeSH
• elektrody MeSH
• financování organizované MeSH
• ganciklovir analýza   chemie   MeSH