Photoreactivation inChlamydomonas reinhardi Dangeard

The existence of photoreactivation in the green unicellular algaChlamydomonas reinhardi Dangeard was demonstrated. The dose reduction factor was constant throughout practically the whole of the dose range and was approximately 0.5. Photoreactivation was not found in cells irradiated with X-rays. The maximum photoreactivation after ultraviolet irradiation was reached after about 30 minutes’ illumination with 2,300Lx. No difference was found between the rate of photoreactivation carried out immediately and 30 minutes after ultraviolet irradiation. The rate of photoreactivation, under the given conditions, seems to be limited chiefly by the supply of light energy. The photoreactivation enzyme is probably a stable component of the cell.     

Fractionation of DNA from Bacillus subtilis and its transforming activity for various markers

The physical, chemical, and functional heterogeneity of tranforming DNA was studied by preparative fractionation techniques providing resolution with respect to differences in molecular weight (gel filtration, sucrose density gradient), base composition (CsCl density gradient), or both these parameters simultaneously (methylalbumin-coated celite 545 MAK column). A comparison of the basic characteristics of the obtained fractions (melting temperature, T _m; density, ; sedimentation coefficient, S _20,w; and transforming activity for ade, leu, and met markers) showed that the factor decisive for functional activity represents, in addition to the sequential arrangement of nucleotides in the chain, the average base composition. Hence, using the methylalbumin column or CsCl density gradient centrifugation, DNA fractions can be isolated which show a several times higher transforming activity for any of the markers examined. By contrast, the remaining fractionation methods, even though considerably decreasing the heterogeneity of the fractions as regards their molecular weight (such as zonal centrifugation), do not offer a possibility of fractionation of the activity for individual markers. This indicates a statistically random degradation of transforming DNA during its isolation. The order of the investigated markers according to their guanine-cytosine content is ade leu met and corresponds also to the order of their positions on the genetic map of Bacillus subtilis.     

Photochemical and Thermal Phases of Chlorophyll a Fluorescence

The measurement of variable chlorophyll (Chl) a fluorescence is widely used as a convenient and versatile tool in photosynthesis research. In many applications empirical correlations and simplified models of Chl a fluorescence are used with success. Nevertheless, variable Chl a fluorescence provides only indirect and complex image of processes occurring within photosynthetic membranes and such simplifications have only limited validity. In this review we elucidate some controversial and still unresolved questions about the origin and interpretation of the variable Chl a fluorescence induction and the proper use of variable Chl a fluorescence for studies of photochemical events in photosystem 2 (PS2). Although the major part of variable Chl a fluorescence reflects the photochemical closure of the PS2 reaction centers (RCs) and can be considered as a function of the redox state of the primary acceptor Q_A, up to 50 % of the change in the Chl a fluorescence yield can be of secondary, nonphotochemical origin. We review the possible sources of the inherent heterogeneity in the origin of variable Chl a fluorescence. We also comment on the practical implications this bears for the use of variable Chl a fluorescence. This revised version was published online in August 2006 with corrections to the Cover Date.     

Peripheral membrane molecules of leukocytes and NK cytotoxicity

Some leukocyte effector cell-surface molecules movement toward the adjoining target cells takes place during the reaction of NK cytotoxicity (NK R). The majority of the moving molecules are usually anchoredvia a divalent-ion-dependent interaction (PMM-M²⁺). The released PMM-M²⁺ can interact also with the secreted tumor necrosis factor alfa (TNF-α). In agreement with PMM-M²⁺ movement, the number of TNF-α binding sites on the target cell surface increases during NK R. In addition, antibodies against PMM-M²⁺, as well asd-mannose- or N-acetyl-d-glucosamine-terminated oligosaccharides of PMM-M²⁺ inhibit NK R. A more detailed analysis of PMM-M²⁺ with monoclonal antibodies used flow cytometry and cell-surface biotinylation. Only 3 of 31 tested CD antigens (CD2, LAK-1 and CD45) were passed through this first strongly restricted experimental screening. The EDTA-released LAK-1 antigen, but not CD2 and CD45, interact with TNF-α and cell surfacevia a mannose-inhibitable interaction dependent on the presence of Ca²⁺ ions. The mechanism of possible participation of PMM-M²⁺ in cytotoxic events is discussed in relation to Ca²⁺ influx and subsequent cytolysin secretion.     

Effect of exogenous hydrogen peroxide on biophoton emission from radish root cells

Biophotons spontaneously emitted from radish root cells were detected using highly sensitive photomultiplier tube. Freshly isolated radish root cells exhibited spontaneous photon emission of about 4 counts s^?1. Addition of hydrogen peroxide to the cells caused significant enhancement in biophoton emission to about 500 counts s^?1. Removal of molecular oxygen using glucose/glucose oxidase system and scavengering of reactive oxygen species by reducing agents such are sodium ascorbate and cysteine completely diminished biophoton emission. Spectral analysis of the hydrogen peroxide-induced biophoton emission indicates that biophotons are emitted mainly in green–red region of the spectra. The data provided by electron paramagnetic resonance spin-trapping technique showed that formation of singlet oxygen observed after addition of H₂O₂ correlates with enhancement in biophoton emission. These observations provide direct evidence that singlet oxygen is involved in biophoton emission from radish root cells.     

Assessment of organic pollution effect considering differences between lotic and lentic stream habitats

Based on the requirements of the Water Framework Directive, a macroinvertebrate-based assessment system to evaluate the ecological quality of streams has been developed by AQEM project consortium. In the Czech Republic the impact of organic pollution was principal pressure studied, but some morphological degradation of some sampling sites could not be avoided. A multimetric assessment system for three stream types was developed. Detrended Correspondence Analysis was used for the detection of the response of macroinvertebrate communities to the gradient of organic degradation. Significant relationships between abiotic (BOD, TOC, nutrients) and biotic (saprobic index, ASPT) indicators of organic enrichment/eutrophication were identified. Separate storage of the riffle and pool components of each multi-habitat sample allowed differences between these habitats to be compared in context of the metrics applied in the assessment system. Lotic and lentic habitats differed in taxonomic composition, ecological traits and biotic indices. The separate assessment of the riffle and pool parts of samples provides additional useful information when combined effects of organic pollution and morphological degradation are to be considered.     

Stepwise Transition of the Tetra-Manganese Complex of Photosystem II to a Binuclear Mn2(μ-O)2 Complex in Response to a Temperature Jump: A Time-Resolved Structural Investigation Employing X-Ray Absorption Spectroscopy

In oxygenic photosynthesis, water is oxidized at a protein-cofactor complex comprising four Mn atoms and, presumably, one calcium. Using multilayers of Photosystem II membrane particles, we investigated the time course of the disassembly of the Mn complex initiated by a temperature jump from 25°C to 47°C and terminated by rapid cooling after distinct heating periods. We monitored polarographically the oxygen-evolution activity, the amount of the Y_D^ox radical and of released Mn²⁺ by EPR spectroscopy, and the structure of the Mn complex by x-ray absorption spectroscopy (XAS, EXAFS). Using a novel approach to analyze time-resolved EXAFS data, we identify three distinct phases of the disassembly process: (1) Loss of the oxygen-evolution activity and reduction of Y_D^ox occur simultaneously (k₁ = 1.0 min⁻¹). EXAFS spectra reveal the concomitant loss of an absorber-backscatterer interaction between heavy atoms separated by ~3.3 Å, possibly related to Ca release. (2) Subsequently, two Mn(III) or Mn(IV) ions seemingly separated by ~2.7 Å in the native complex are reduced to Mn(II) and released (k₂ = 0.18 min⁻¹). The x-ray absorption spectroscopy data is highly suggestive that the two unreleased Mn ions form a di-μ-oxo bridged Mn(III)₂ complex. (3) Finally, the tightly-bound Mn₂(μ-O)₂ unit is slowly reduced and released (k₃ = 0.014 min⁻¹).     

Modeling of quantal neurotransmitter release kinetics in the presence of fixed and mobile calcium buffers

The local calcium concentration in the active zone of secretion determines the number and kinetics of neurotransmitter quanta released after the arrival of a nerve action potential in chemical synapses. The small size of mammalian neuromuscular junctions does not allow direct measurement of the correlation between calcium influx, the state of endogenous calcium buffers determining the local concentration of calcium and the time course of quanta exocytosis. In this work, we used computer modeling of quanta release kinetics with various levels of calcium influx and in the presence of endogenous calcium buffers with varying mobilities. The results of this modeling revealed the desynchronization of quanta release under low calcium influx in the presence of an endogenous fixed calcium buffer, with a diffusion coefficient much smaller than that of free Ca²⁺, and synchronization occurred upon adding a mobile buffer. This corresponds to changes in secretion time course parameters found experimentally (Samigullin et al., Physiol Res 54:129–132, 2005; Bukharaeva et al., J Neurochem 100:939–949, 2007).