Kinetics of reformation of the S state capable of progressing to the S state after the O release by photosystem II.

The active site for water oxidation in photosystem II (PSII) comprises a MnCaO cluster adjacent to a redox-active tyrosine residue (Tyr). During the water-splitting process, the enzyme transitions through five sequential oxidation states (S to S), with O evolution occurring during the STyr· to STyr transition. Chloride also plays a role in this mechanism.

Diatom phytochromes integrate the underwater light spectrum to sense depth.

Aquatic life is strongly structured by the distribution of light, which, besides attenuation in intensity, exhibits a continuous change in the spectrum with depth. The extent to which these light changes are perceived by phytoplankton through photoreceptors is still inadequately known. We addressed this issue by integrating functional studies of diatom phytochrome (DPH) photoreceptors in model species with environmental surveys of their distribution and activity.

In vivo ElectroChromic Shift measurements of photosynthetic activity in far-red absorbing cyanobacteria.

Some cyanobacteria can do photosynthesis using not only visible but also far-red light that is unused by most other oxygenic photoautotrophs because of its lower energy content. These species have a modified photosynthetic apparatus containing red-shifted pigments. The incorporation of red-shifted pigments decreases the photochemical efficiency of photosystem I and, especially, photosystem II, and it might affect the distribution of excitation energy between the two photosystems with possible consequences on the activity of the entire electron transport chain.

The control of nitric oxide dynamics and interaction with substituted zinc-phthalocyanines.

Phthalocyanines are artificial macrocycles that can harbour a central metal atom with four symmetric coordinations. Similar to metal-porphyrins, metal-phthalocyanines (M-PCs) may bind small molecules, especially diatomic gases such as NO and O. Furthermore, various chemical chains can be grafted at the periphery of the M-PC macrocycle, which can change its properties, including the interaction with diatomic gases.

Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [PP].

Flash-induced absorption changes in the Soret region arising from the [PP] state, the chlorophyll cation radical formed upon light excitation of Photosystem II (PSII), were measured in Mn-depleted PSII cores at pH 8.6. Under these conditions, Tyr is i) reduced before the first flash, and ii) oxidized before subsequent flashes.