V. N. Kurashov

Hybrid system based on quantum dots and photosystem 2 core complex

We show that semiconductor nanocrystals (quantum dots, QD) can be used to increase the absorption capacity of pigment-protein complexes. In a mixture of photosystem 2 core complex (PS2) and QD, the fluorescence of the latter decreases several-fold due to the transfer of the absorbed energy to the PS2 core complex. We discuss Forster’s inductive-resonance mechanism as a possible way of energy transfer in donor-acceptor pairs QD-PS2 core complex. Calculations based on the experimental data show that the enhancement of PS2 fluorescence and the rate of QA reduction increase up to 60% due to efficient energy migration from QD to PS2.

Photochemical properties of photosystem 1 immobilized in a mesoporous semiconductor matrix

The pigment-protein complex of photosystem 1 (PS1) isolated from cyanobacterium Synechocystis sp. PCC 6803 has been adsorbed on a solid mesoporous film made from TiO2 nanoparticles. was on The TiO2 film supported on a glass substrate with a surface area of 1 cm2 adsorbs up to 0.045 nmol of PS1. PS1 molecules are distributed in the pores of the mesoporous support. Immobilization has an insignificant effect on the optical and photochemical properties of PS1. A reversible photoinduced EPR signal from the oxidized primary electron donor P700 of immobilized PS1 has been detected. It has been shown by photoelectrochemical methods that the photoexcitation of PS1 results in electron injection from PS1 to the conduction band of TiO2.

Transmembrane charge transfer in photosynthetic reaction centers: some similarities and distinctions.

This mini review presents a general comparison of structural and functional peculiarities of three types of photosynthetic reaction centers (RCs)--photosystem (PS) II, RC from purple bacteria (bRC) and PS I. The nature and mechanisms of the primary electron transfer reactions, as well as specific features of the charge transfer reactions at the donor and acceptor sides of RCs are considered. Comparison of photosynthetic RCs shows general similarity between the core central parts of all three types, between the acceptor sides of bRC and PS II, and between the donor sides of bRC and PS I. In the latter case, the similarity covers thermodynamic, kinetic and dielectric properties, which determine the resemblance of mechanisms of electrogenic reduction of the photooxidized primary donors. Significant distinctions between the donor and acceptor sides of PS I and PS II are also discussed. The results recently obtained in our laboratory indicate in favor of the following sequence of the primary and secondary electron transfer reactions: in PS II (bRC): Р(680)(Р(870)) → Chl(D1)(В(А)) → Phe(bPhe) → Q(A); and in PS I: Р(700) → А(0А)/A(0B) → Q(A)/Q(B).

Investigation of the low-affinity oxidation site for exogenous electron donors in the Mn-depleted photosystem II complexes

In the manganese-depleted photosystem II (PSII[-Mn]) preparations, oxidation of exogenous electron donors is carried out through the high-affinity (HA) and the low-affinity (LA) sites. This paper investigates the LA oxidation site in the PSII(-Mn) preparations where the HA, Mn-binding site was blocked with ferric cations [[11] B.K. Semin, M.L. Ghirardi, M. Seibert, Blocking of electron donation by Mn(II) to Y(Z)(*) following incubation of Mn-depleted photosystem II membranes with Fe(II) in the light, Biochemistry 41 (2002) 5854-5864.]. In blocked (PSII[-Mn,+Fe]) preparations electron donation by Mn(II) cations to Y(Z)(*) was not detected at Mn(II) concentration 10 microM (corresponds to K(m) for Mn(II) oxidation at the HA site), but detected at Mn concentration 100 microM (corresponds to K(m) for the LA site) by fluorescence measurements. Comparison of pH-dependencies of electron donation by Mn(II) through the HA and the LA sites revealed the similar pK(a) equal to 6.8. Comparison of K(m) for diphenylcarbazide (DPC) oxidation at the LA site and K(d) for A(T) thermoluminescence band suppression by DPC in PSII(-Mn,+Fe) samples suggests that there is relationship between the LA site and A(T) band formation. The role of D1-His190 as an oxidant of exogenous electron donors at the LA site is discussed. In contrast to electrogenic electron transfer from Mn(II) at the HA site to Y(Z)(*), photovoltage due to Mn(II) oxidation in iron-blocked PSII(-Mn) core particles was not detected.

Manganese-depleted/reconstituted photosystem II core complexes in solution and liposomes

Chlorophyll fluorescence transients measurements were employed to study the functioning of spinach photosystem II (PS II) core complexes in solution or reconstituted into liposomes. Lipid vesicles were prepared from soybean phospholipids (asolectine) or a mixture of spinach thylakoid lipids. In comparison with intact PS II core complexes comprising two distinct fluorescence phases, designated as O-J and J-P, complete suppression of the latter phase in Mn-depleted samples was observed. An increase of magnitude of the J-P phase in the presence of exogenous MnCl(2) (4 Mn/RC) indicate in favor of partial restoring of oxygen-evolution activity of PS II. The J-P phase observed in PS II in solution was characterized by a lifetime of ~320 ms, while in liposome-reconstituted samples this phase was accelerated up to ~20 ms in case of asolectine and up to ~9 ms in case of a mixture of thylakoid lipids. These data clearly suggest that lipid environment stimulates the steady-state rate of oxygen evolution. The effect of lipids is likely based on keeping the embedded proteins in optimal structure for efficient functioning.

Effect of Dehydrated Trehalose Matrix on the Kinetics of Forward Electron Transfer Reactions in Photosystem i

Abstract The effect of dehydration on the kinetics of forward electron transfer (ET) has been studied in cyanobacterial photosystem I (PS I) complexes in a trehalose glassy matrix by time-resolved optical and EPR spectroscopies in the 100 fs to 1 ms time domain. The kinetics of the flash-induced absorption changes in the subnanosecond time domain due to primary and secondary charge separation steps were monitored by pump–probe laser spectroscopy with 20-fs low-energy pump pulses centered at 720 nm. The back-reaction kinetics of P700 were measured by high-field time-resolved EPR spectroscopy and the forward kinetics of A1A•−/A1B•−→FX

Vectorial charge transfer reactions on the donor side of manganese-depleted and reconstituted photosystem 2 core complexes

{\rm{A}}_{{\rm{1A}}}^{ \bullet - }/{\rm{A}}_{1{\rm{B}}}^{ \bullet - } \to {{\rm{F}}_{\rm{X}}}

Electron transfer between exogenous electron donors and reaction center of photosystem 2.

by time-resolved optical spectroscopy at 480 nm. The kinetics of the primary ET reactions to form the primary P700•+A0•−

Critical evaluation of electron transfer kinetics in P700–FA/FB, P700–FX, and P700–A1 Photosystem I core complexes in liquid and in trehalose glass

{\rm{P}}_{700}^{ \bullet + }{\rm{A}}_0^{ \bullet - }

Transmembrane electric potential difference in the protein-pigment complex of photosystem 2.

and the secondary P700•+A1•−