Measurements of Oxygen Evolution in Photosynthesis.

This chapter compares two different techniques for monitoring photosynthetic O production; the wide-spread Clark-type O electrode and the more sophisticated membrane inlet mass spectrometry (MIMS) technique. We describe how a simple membrane inlet for MIMS can be made out of a commercial Clark-type cell and outline the advantages and drawbacks of the two techniques to guide researchers in deciding which method to use. Protocols and examples are given for measuring O evolution rates and for determining the number of chlorophyll molecules per active photosystem II reaction center.

Flavodiiron-mediated O photoreduction at photosystem I acceptor-side provides photoprotection to conifer thylakoids in early spring.

Green organisms evolve oxygen (O) via photosynthesis and consume it by respiration. Generally, net O consumption only becomes dominant when photosynthesis is suppressed at night. Here, we show that green thylakoid membranes of Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies) needles display strong O consumption even in the presence of light when extremely low temperatures coincide with high solar irradiation during early spring (ES).

Solar energy conversion by photosystem II: principles and structures.

Photosynthetic water oxidation by Photosystem II (PSII) is a fascinating process because it sustains life on Earth and serves as a blue print for scalable synthetic catalysts required for renewable energy applications. The biophysical, computational, and structural description of this process, which started more than 50 years ago, has made tremendous progress over the past two decades, with its high-resolution crystal structures being available not only of the dark-stable state of PSII, but of all the semi-stable reaction intermediates and even some transient states. Here, we summarize the current knowledge on PSII with emphasis on the basic principles that govern the conversion of light energy to chemical energy in PSII, as well as on the illustration of the molecular structures that enable these reactions.

Acetylacetone Interferes with Carbon and Nitrogen Metabolism of by Cutting Off the Electron Flow to Ferredoxin.

The regulation of photosynthetic machinery with a nonoxidative approach is a powerful but challenging strategy for the selective inhibition of bloom-forming cyanobacteria. Acetylacetone (AA) was recently found to be a target-selective cyanocide for , but the cause and effect in the studied system are still unclear. By recording of the chemical fingerprints of the cells at two treatment intervals (12 and 72 h with 0.

Nitric oxide represses photosystem II and NDH-1 in the cyanobacterium Synechocystis sp. PCC 6803.

Photosynthetic electron transfer comprises a series of light-induced redox reactions catalysed by multiprotein machinery in the thylakoid. These protein complexes possess cofactors susceptible to redox modifications by reactive small molecules. The gaseous radical nitric oxide (NO), a key signalling molecule in green algae and plants, has earlier been shown to bind to Photosystem (PS) II and obstruct electron transfer in plants.

Regulation of Photosynthesis in Bloom-Forming Cyanobacteria with the Simplest β-Diketone.

Selective inhibition of photosynthesis is a fundamental strategy to solve the global challenge caused by harmful cyanobacterial blooms. However, there is a lack of specificity of the currently used cyanocides, because most of them act on cyanobacteria by generating nontargeted oxidative stress. Here, for the first time, we find that the simplest β-diketone, acetylacetone, is a promising specific cyanocide, which acts on through targeted binding on bound iron species in the photosynthetic electron transport chain, rather than by oxidizing the components of the photosynthetic apparatus.

Three overlooked photosynthesis papers of Otto Warburg (1883-1970), published in the 1940s in German and in Russian, on light-driven water oxidation coupled to benzoquinone reduction.

After a brief background on Otto Heinrich Warburg (1883-1970), and some of his selected research, we provide highlights, in English, of three of his papers in the 1940s-unknown to many as they were not originally published in English. They are: two brief reports on Photosynthesis, with Wilhelm Lüttgens, originally published in German, in 1944: 'Experiment on assimilation of carbonic acid'; and 'Further experiments on carbon dioxide assimilation'. This is followed by a regular paper, originally published in Russian, in 1946: 'The photochemical reduction of quinone in green granules'.

Water oxidation by photosystem II is the primary source of electrons for sustained H photoproduction in nutrient-replete green algae.

The unicellular green alga is capable of photosynthetic H production. H evolution occurs under anaerobic conditions and is difficult to sustain due to 1) competition between [FeFe]-hydrogenase (Hase), the key enzyme responsible for H metabolism in algae, and the Calvin-Benson-Bassham (CBB) cycle for photosynthetic reductants and 2) inactivation of Hase by O coevolved in photosynthesis. Recently, we achieved sustainable H photoproduction by shifting algae from continuous illumination to a train of short (1 s) light pulses, interrupted by longer (9 s) dark periods.

Bicarbonate-Mediated CO Formation on Both Sides of Photosystem II.

The effect of bicarbonate (HCO) on photosystem II (PSII) activity was discovered in the 1950s, but only recently have its molecular mechanisms begun to be clarified. Two chemical mechanisms have been proposed. One is for the electron-donor side, in which mobile HCO enhances and possibly regulates water oxidation by acting as proton acceptor, after which it dissociates into CO and HO.

Assessment of the manganese cluster's oxidation state via photoactivation of photosystem II microcrystals.

Knowledge of the manganese oxidation states of the oxygen-evolving MnCaO cluster in photosystem II (PSII) is crucial toward understanding the mechanism of biological water oxidation. There is a 4 decade long debate on this topic that historically originates from the observation of a multiline electron paramagnetic resonance (EPR) signal with effective total spin of S = 1/2 in the singly oxidized S state of this cluster. This signal implies an overall oxidation state of either Mn(III)Mn(IV) or Mn(III)Mn(IV) for the S state.

'Birth defects' of photosystem II make it highly susceptible to photodamage during chloroplast biogenesis.

High solar flux is known to diminish photosynthetic growth rates, reducing biomass productivity and lowering disease tolerance. Photosystem II (PSII) of plants is susceptible to photodamage (also known as photoinactivation) in strong light, resulting in severe loss of water oxidation capacity and destruction of the water-oxidizing complex (WOC). The repair of damaged PSIIs comes at a high energy cost and requires de novo biosynthesis of damaged PSII subunits, reassembly of the WOC inorganic cofactors and membrane remodeling.

Structures of the intermediates of Kok's photosynthetic water oxidation clock.

Inspired by the period-four oscillation in flash-induced oxygen evolution of photosystem II discovered by Joliot in 1969, Kok performed additional experiments and proposed a five-state kinetic model for photosynthetic oxygen evolution, known as Kok's S-state clock or cycle. The model comprises four (meta)stable intermediates (S, S, S and S) and one transient S state, which precedes dioxygen formation occurring in a concerted reaction from two water-derived oxygens bound at an oxo-bridged tetra manganese calcium (MnCaO) cluster in the oxygen-evolving complex. This reaction is coupled to the two-step reduction and protonation of the mobile plastoquinone Q at the acceptor side of PSII.

Tumor antigen glycosaminoglycan modification regulates antibody-drug conjugate delivery and cytotoxicity.

Aggressive cancers are characterized by hypoxia, which is a key driver of tumor development and treatment resistance. Proteins specifically expressed in the hypoxic tumor microenvironment thus represent interesting candidates for targeted drug delivery strategies. Carbonic anhydrase (CAIX) has been identified as an attractive treatment target as it is highly hypoxia specific and expressed at the cell-surface to promote cancer cell aggressiveness.