Temperature Dependence of Tryptophan Fluorescence Lifetime as an Indicator of Its Microenvironment Dynamics.

The spectral-kinetic characteristics of the fluorescence of the tryptophan molecule in an aqueous solution and in the composition of a protein (albumin) were studied in the temperature range from -170 to 25°C. To explain the observed changes in the spectra and the tryptophan fluorescence lifetime with temperature, a model of transitions between the excited and ground states involving a charge-transfer state was used, which takes into account the nonlinear nature of the dynamics of these transitions. In these processes, an important role is played by the interaction of tryptophan molecules with its microenvironment, as well as rearrangements in the system of hydrogen bonds of the water-protein matrix surrounding the tryptophan molecule.

Photophysical Properties of Upconverting Nanoparticle-Phthalocyanine Complexes.

Interaction between upconverting nanoparticles and aluminum octacarboxyphthalocyanine was studied. The efficiency of non-radiative energy transfer from the nanoparticles to phthalocyanine increased with the number of phthalocyanine molecules adsorbed on the nanoparticle, but only up to a certain limit. Further increase in the phthalocyanine concentration resulted in a decrease of its sensitized fluorescence due to the dimerization of dye molecules on the nanoparticle surface. When subjected to infrared irradiation, phthalocyanine molecules in the hybrid complex generated singlet oxygen. The observed effects are of interest in regard to the targeted search for new components of efficient third-generation hybrid photosensitizers.

Relaxation processes accompanying electron stabilization in the quinone acceptor part of Rb. sphaeroides reaction centers.

The temperature dependence of the dark recombination rate in photooxidized bacteriochlorophyll (P) and photoreduced quinone acceptors (ubiquinones) QA and QB of photosynthetic reaction centers of purple bacteria Rhodobacter sphaeroides (Rb. sphaeroides) was studied. Photoinduced changes in the absorption were detected in the Qx absorption band of photooxidized bacteriochlorophyll at 600 nm and in the bands corresponding to the redox changes of ubiquinones at 335 and 420-450 nm. Kinetic analysis was used to evaluate the activation energy and the characteristic time of the transient process of relaxation accompanying electron stabilization at the final quinone acceptor. A comparative study of the kinetics of oxidation-reduction reactions of photoactive bacteriochlorophyll RC purple bacteria and quinone acceptors in their individual absorption bands is an informative approach to studying the mechanisms of this stabilization. The analysis of the revealed kinetic differences makes it possible to estimate the activation energy and the characteristic times of the transition relaxation processes associated with the stabilization of the electron in the quinone acceptor part of RC. Purple bacterial reaction centers have fundamental similarities with PSII reaction centers. Such a similarity represents evolutional closeness between the two types of RC. So it is possible that the photoinduced charge separation in PSII RC, as well as in purple bacteria RC, is also accompanied by definite conformational changes. The possible role of hydrogen bonds of surrounding protein in the relaxation processes accompanying the electron transfer to quinone acceptors is discussed.

Temperature Dependence of Tryptophan Fluorescence Lifetime in Aqueous Glycerol and Trehalose Solutions.

The temperature dependences of tryptophan fluorescence decay kinetics in aqueous glycerol and 1 M trehalose solutions were examined. The fluorescence decay kinetics were recorded in the spectral region of 292.5-417.5 nm with nanosecond time resolution. The kinetics curves were approximated by the sum of three exponential terms, and the spectral distribution (DAS) of these components was determined. An antisymbatic course of fluorescence decay times of two (fast and medium) components in the temperature range from -60 to +10°C was observed. The third (slow) component showed only slight temperature dependence. The antisymbatic behavior of fluorescence lifetimes of the fast and medium components was explained on the assumption that some of the excited tryptophan molecules are transferred from a short-wavelength B-form with short fluorescence lifetime to a long-wavelength R-form with an intermediate fluorescence lifetime. This transfer occurred in the indicated temperature range.

Generation of radical form of dipyridamole at illumination of photosynthetic reaction centers of Rb. sphaeroides.

The study of the effect of vasodilator, antiplatelet agent, and inhibitor P-glycoprotein dipyridamole (DIP) on the functioning of the transmembrane protein of the reaction center (RC) of Rb. sphaeroides showed that the activation of RC by constant light generates the DIP radical cation, which significantly affects the kinetics of recombination of charges divided between photoactive bacteriochlorophyll and quinone acceptors. Thus, the antioxidant properties of DIP may affect the functional activity of membrane proteins, and this apparently should be taken into account in the studies of the mechanisms of therapeutic action of this drug.

Influence of trehalose on high-temperature stability of the photosynthetic reaction centers.

The effect of heating at 65°C for 20 min on the absorption spectra and kinetics of the dark recombination of charges separated between photoactive bacteriochlorophyll and quinone acceptors was studied in dry films of bacterial photosynthetic reaction centers (RCs), RC films in polyvinyl alcohol, and trehalose. A pronounced protective effect of trehalose against pheophytinizaiton of molecules bacteriochlorophylls in RC structure and in maintaining their higher photochemical activity was found.

Non-photochemical Fluorescence Quenching in Photosystem II Antenna Complexes by the Reaction Center Cation Radical.

In direct experiments, rate constants of photochemical (kP) and non-photochemical (kP(+)) fluorescence quenching were determined in membrane fragments of photosystem II (PSII), in oxygen-evolving PSII core particles, as well as in core particles deprived of the oxygen-evolving complex. For this purpose, a new approach to the pulse fluorometry method was implemented. In the "dark" reaction center (RC) state, antenna fluorescence decay kinetics were measured under low-intensity excitation (532 nm, pulse repetition rate 1 Hz), and the emission was registered by a streak camera. To create a "closed" [P680(+)QA(-)] RC state, a high-intensity pre-excitation pulse (pump pulse, 532 nm) of the sample was used. The time advance of the pump pulse against the measuring pulse was 8 ns. In this experimental configuration, under the pump pulse, the [P680(+)QA(-)] state was formed in RC, whereupon antenna fluorescence kinetics was measured using a weak testing picosecond pulsed excitation light applied to the sample 8 ns after the pump pulse. The data were fitted by a two-exponential approximation. Efficiency of antenna fluorescence quenching by the photoactive RC pigment in its oxidized (P680(+)) state was found to be ~1.5 times higher than that of the neutral (P680) RC state. To verify the data obtained with a streak camera, control measurements of PSII complex fluorescence decay kinetics by the single-photon counting technique were carried out. The results support the conclusions drawn from the measurements registered with the streak camera. In this case, the fitting of fluorescence kinetics was performed in three-exponential approximation, using the value of τ1 obtained by analyzing data registered by the streak camera. An additional third component obtained by modeling the data of single photon counting describes the P680(+)Pheo(-) charge recombination. Thus, for the first time the ratio of kP(+)/kP = 1.5 was determined in a direct experiment. The mechanisms of higher efficiency for non-photochemical antenna fluorescence quenching by RC cation radical in comparison to that of photochemical quenching are discussed.

The efficiency of non-photochemical fluorescence quenching by cation radicals in photosystem II reaction centers.

In a direct experiment, the rate constants of photochemical k p and non-photochemical k p+ quenching of the chlorophyll fluorescence have been determined in spinach photosystem II (PS II) membrane fragments, oxygen-evolving PS II core, as well as manganese-depleted PS II particles using pulse fluorimetry. In the dark-adapted reaction center(s) (RC), the fluorescence decay kinetics of the antenna were measured at low-intensity picosecond pulsed excitation. To create a "closed" P680+Q A- state, RCs were illuminated by high-intensity actinic flash 8 ns prior to the measuring flash. The obtained data were approximated by the sum of two decaying exponents. It was found that the antennae fluorescence quenching efficiency by the oxidized photoactive pigment of RC P680+ was about 1.5 times higher than that of the neutral P680 state. These results were confirmed by a single-photon counting technique, which allowed to resolve the additional slow component of the fluorescence decay. Slow component was assigned to the charge recombination of P680+Pheo- in PS II RC. Thus, for the first time, the ratio k p+ /k p â‰… 1.5 was found directly. The mechanism of the higher efficiency of non-photochemical quenching comparing to photochemical quenching is discussed.

[The fasciolosis epizootic situation in Russia].

The fasciolosis epizootic situation in Russia is assessed on the zonal basis of the spread of this helminthism. The authors state the causes of varying degrees of this infection in animals and its spread zones in regional and latitude aspects: a problem-free zone, a low infection spread zone, a zone of periodic outbreaks, and that of persistent fasciolosis.

[Toxocariasis under the present conditions].

Toxocariasis is today the most widespread zoonotic, helminthic infection in Russia and other countries of the world. A large population of Toxocara has recently inhabited the urban populations of dogs and cats. Therefore toxocariasis canis and toxocariasis cati have shifted from rural areas to cities and megalopolises where Toxocara canis infestation amounts to as much as 100%, without excluding that in the rural populations of dogs. Due to the fact that the number of dogs and cats has considerably increased (20% of adult dogs and 80% of puppies are infected with Toxocara) in our megalopolises, cities, and urban communities as in foreign countries, this substantially increases the risk of toxacariasis. From the above reasoning, environmental contamination with Toxacara eggs creates an important reservoir of infestation for humans and animals (the contamination rates in different regions of Russia ranges from 1-3 to 50-60%, with the infestation rates of 1 - 10 eggs per 100 g of soil). Human toxocariasis is polymorphic, from its subclinical course to significant organ pathology, and detectable as a manifestation of eosinophilia, fever, hepatomegaly, hyperglobulinemia, lung and central nervous system lesions, myocarditis, and skin rash. The diagnosis of toxocariasis is established by its clinical presentation and serological findings. It is important in the history that children have spent much time with dogs or cats.

[Use of the standard theory of electronic transitions in the description of oscillations in the kinetics of electron transfer in reaction centers of purple bacteria].

The standard theory of the electron transfer between donor and acceptor molecules was used to describe oscillations in the reduction kinetics of the intermediate electron acceptor BA and the primary electron acceptor HA. The kinetics of the reduction of BA and HA were simulated on the basis of the model in which one and two accepting modes were used. A principal experiment is offered for the selection of the suitable theory for adequate description of oscillations in the kinetics of electron transfer in the reaction centers of purple bacteria.

[Gastrodiscoidosis is a dangerous zoonosis].

The paper gives data on the helminthiasis--gastrodiscoidosis, a zoonotic disease caused by the trematode Gastrodiscoides hominis (Lewis et McConnall, 1876) parasitizing in the animal and human intestine in the endemic foci of both Russia and foreign countries. It also presents information on the morphology of the helminth, the biological cycle of development of the parasite and its habitat and spread, as well as its induced abnormalities and on the method of diagnosing of the disease.

[The current canine and feline parasitic diseases situation in the megapolis of Moscow].

The paper describes the epizootic situation associated with parasitic diseases in dogs and cats in the megapolis of Moscow. The situation becomes particular dangerous in the dogs kept in the flats of the city's dwellers wherein 30 (28%) out of the 107 dogs examined have been found to be infested with T. canis, T. leonine, T. vulpis, Taenia sp., D. caninum, and two protozoan species: Cystoisospora canis and C. ohioenensis. Out of the 80 cats examined, there are 22 (27.5%) infested cats. T. mystax, T. leonine, Taenia sp., and Cystoisospora felis are detectable in this group of the animals. This situation constitutes a serious hazard in the infection of the city's population with zoonoses.