The lack of ability of carcinogens and non-carcinogenic analogs to induce sex-linked recessive lethals in Drosophila melanogaster

The mutagenic activity of two known carcinogens (benzo(a) pyrene and 2-acetylaminofluorene) and that of two structurally closely related but not carcinogenic compounds (pyrene and 4-acetylaminofluorene) was examined by the Muller-5 test for sex-linked recessive lethals (SRL). The chemicals tested were applied to the food medium for larvae of Canton-S Drosophila melanogaster. No statistically significant differences in frequencies of induced SRL were found either within pairs of chemicals or between treated and untreated animals.     

Thermal stability of electron transport in PS II membranes and particles from the thermophilic cyanobacteria

Thermal stability of the ferricyanide (FC) and dichlorophenolindophenol (DCIP) reducing reactions was investigated in isolated membrane preparations and PS II particles with active water splitting system from the cyanobacterium Synechococcus elongatus. In a hypotonic medium, the thermostability was seen to be much higher for the DCIP than for the FC reduction reaction. After the addition of high concentrations of polyethylene glycol (Mwt = 4000) or sodium citrate to the medium, the FC reduction reaction appeared to be more temperature resistant. Data on the effects of temperature, DCMU and detergents on the electron transfer rate in PS II provide evidence suggesting that the different thermal stabilities of the two reactions are due to different physico-chemical properties of the electron donor sites to FC and DCIP. The data suggest that regions of contact between individual macromolecular complexes of the electron transport chain are the most labile sites of the photosynthetic apparatus. The role of the composition and properties of the intracellular medium on thermostability are emphasized.     

The highly diverged trypanosomal MICOS complex is organized in a nonessential integral membrane and an essential peripheral module

The mitochondrial contact site and cristae organization system (MICOS) mediates the formation of cristae, invaginations in the mitochondrial inner membrane. The highly diverged MICOS complex of the parasitic protist Trypanosoma brucei consists of nine subunits. Except for two Mic10‐like and a Mic60‐like protein, all subunits are specific for kinetoplastids. Here, we determined on a proteome‐wide scale how ablation of individual MICOS subunits affects the levels of the other subunits. The results reveal co‐regulation of TbMic10‐1, TbMic10‐2, TbMic16 and TbMic60, suggesting that these nonessential, integral inner membrane proteins form an interdependent network. Moreover, the ablation of TbMic34 and TbMic32 reveals another network consisting of the essential, intermembrane space‐localized TbMic20, TbMic32, TbMic34 and TbMic40, all of which are peripherally associated with the inner membrane. The downregulation of TbMic20, TbMic32 and TbMic34 also interferes with mitochondrial protein import and reduces the size of the TbMic10‐containing complexes. Thus, the diverged MICOS of trypanosomes contains two subcomplexes: a nonessential membrane‐integrated one, organized around the conserved Mic10 and Mic60, that mediates cristae formation, and an essential membrane‐peripheral one consisting of four kinetoplastid‐specific subunits, that is required for import of intermembrane space proteins.     

Mossbauer spectroscopic study of functional thermal destruction of iron--sulfur proteins in membranes of thermophilic cyanobacteria synechococcus elongatus

A mathematical model of the Mossbauer spectrum (80K) of native membranes of Synechococcus elongatus was constructed on the basis of values of the quadruple splitting (Delta) and the isomeric shift (delta) of the iron-containing components of the photosynthetic apparatus obtained from the literature. Thermally induced changes in the intensity of the spectral components of membranes and isolated preparations of photosystem (PS) I were studied using this model. It was shown that exposure of membranes to 70-80 degrees C causes a decrease in the intensity of the components related to the FX, FA, and FB centers and surface-located ferredoxins of PS I, an increase in the intensity of the doublets of oxidized iron clusters that are nonspecifically absorbed by the membranes, and formation of a new doublet. Spectral parameters of this doublet (Delta = 3.10 mm/sec and delta = 1.40 mm/sec) are typical of inorganic hydrated forms of reduced iron. Heating of PS I preparations also causes a decrease in the intensity of doublets of the FX, FA, and FB centers and an increase in the intensity of doublets of nonspecifically bound oxidized iron. However, this does not cause formation of inorganic reduced iron. Comparison between the intensities of the Mossbauer spectral components in intact and heated samples suggests that the main source of reduced iron in membranes is surface-located ferredoxins. Nonspecifically bound oxidized iron is formed at the expense of the FX, FA, and FB centers. Disappearance of spectral components associated with ferredoxins and accumulation of reduced iron in membranes occur within the temperature range critical for inhibition of electron transport through PS I to oxygen. These findings suggest that the thermally induced processes of accumulation of reduced iron and inhibition of electron transport in PS I in membranes of thermophilic cyanobacteria are interrelated and caused mainly by degradation of the Fe--S centers of ferredoxins. The possible role of reduced iron accumulation in the degradation of the photosynthetic apparatus induced by heat and other extreme physical and chemical factors is discussed.     

Oxidative Processes in Photosystem I of Thermophilic Cyanobacteria at High Temperatures

We studied the mechanisms of the relationships between the generation of millisecond delayed fluorescence in photosystem I (DF) and the oxidative destruction of chlorophyll in the membranes of a thermophilic cyanobacteria Synechococcus elongatusin the temperature range 60–80°C at various irradiation levels and in the presence of substances affecting the intensity of DF. Light and temperature dependencies of the chlorophyll oxidation rates were similar to those of the DF of PSI. Anions Cl^–, Br^–, and NO^– ₃, which quench the triplet states of chlorophyll, almost completely inhibited the chlorophyll oxidation and reduced the intensity of the DF maximum by 70%. Under anaerobic conditions and in the presence of sodium ascorbate, the rate of chlorophyll oxidation also markedly decreased. We found that the long-wavelength chlorophyll forms were the most susceptible to oxidation and related the temperature-dependent changes in the DF of PSI and in the oxidative processes in the membranes of thermophilic cyanobacteria to an increase in the concentration of the triplet states of P₇₀₀and other chlorophyll forms. The latter result from the temperature-dependent inactivation of carotenoids and the inhibition of electron transfer to ferredoxin in PSI.     

The Diverged Trypanosome MICOS Complex as a Hub for Mitochondrial Cristae Shaping and Protein Import

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Comparative Study of Thermal Degradation of Iron–Sulfur Proteins in Spinach Chloroplasts and Membranes of Thermophilic Cyanobacteria: Mössbauer Spectroscopy

Mössbauer spectra of chloroplasts isolated from spinach plants grown in a mineral medium enriched with ⁵⁷Fe and Mössbauer spectra of native membranes of the thermophilic cyanobacterium Synechococcus elongatus contain a broad asymmetric doublet typical of the iron–sulfur proteins of Photosystem (PS) I. Exposure of chloroplasts to temperatures of 20-70°C significantly modifies the central part of the spectra. This spectral change is evidence of decreased magnitude of the quadrupole splitting. However, the thermally induced doublet (Q = 3.10 mm/sec and = 1.28 mm/sec) typical of hydrated forms of reduced (divalent) inorganic iron is not observed in spinach chloroplasts. This doublet is usually associated with degradation of active centers of ferredoxin, a surface-exposed protein of PS I. The Mössbauer spectra of photosynthetic membranes of spinach chloroplasts and cyanobacteria were compared using the probability distribution function of quadrupole shift (1/2 quadrupole splitting Q) of trivalent iron. The results of calculation of these functions for the two preparations showed that upon increasing the heating temperature there was a decrease in the probability of the presence of native iron–sulfur centers F_X, F_A, and F_B (quadrupole shift range, 0.43-0.67 mm/sec) in heated preparations. This process was also accompanied by an increase in the probability of appearance of clusters of trivalent iron. This increase was found to be either gradual and continuous or abrupt and discrete in photosynthetic membranes of cyanobacteria or spinach chloroplasts, respectively. The probability of the presence of the iron–sulfur centers F_X, F_A, and F_B in chloroplasts abruptly decreases to virtually to zero within the temperature range critical for inhibition of electron transport through PS I to oxygen. In cyanobacteria, both thermal destruction of iron–sulfur centers of PS I and functional degradation of PS I are shifted toward a higher temperature. The results of this study suggest that the same mechanism of thermal destruction of the PS I core occurs in both thermophilic and mesophilic organisms: destruction of iron–sulfur centers F_X, F_A, and F_B, release of oxidized (trivalent) iron, and its accumulation in membrane-bound iron-oxo clusters.     

Genetics of partial trisomies. I. Trisomy 2q

The family, where 2 children had partial trisomy 2q33-q ter, due to paternal translocation t(2;18) (q33;p11.1), was examined. The analysis of 36 cases of trisomy 2q showed that the forms connected with parental chromosomal rearrangement prevailed in the genesis of trisomy 2q. Moreover, the balanced carrier-mothers were more common than fathers. The 2q34-q ter segment may be considered "critical" for occurrence of trisomy 2q syndrome. In case of equal triplication, the similarity between the patients within the same family is greater than between those from different families. The value of intragroup similarity between the patients with equal trisomies may be used for evaluation of phenotypical similarity at different triplicated segments.     

Thermally-induced delayed fluorescence of photosystem I and II chlorophyll in thermophilic cyanobacterium Synechococcus elongatus.

Stationary delayed fluorescence (DF) of chlorophyll in isolated membrane preparations from thermophilic cyanobacterium Synechococcus elongatus was investigated as a function of temperature. Two peaks at different temperatures were observed. The low-temperature peak (54-60 degrees C) coincided with the main maximum of the thermally-induced delayed fluorescence of chlorophyll in intact cells and PSII-particles with active oxygen-evolving system. The high-temperature peak (78 degrees C) coincided with the minor band of delayed light emitted by intact cells. It was also observed in the delayed fluorescence emission from a PSI-enriched fraction preparation. The intensities of the DF peaks were dependent on the presence of inhibitors, donors and acceptors that cause specific effects on electron transport of the two photosystems. The low-temperature and high-temperature peaks were related to PSII and PSI, respectively. The manifestation of delayed fluorescence from PSI and PSII at different temperatures seems to be a specific property of thermophilic cyanobacteria. The reason for this may be a high thermal stability of the photosystems and the lack of the PSII antenna complex in isolated membranes. Consequently, the relative yield of delayed fluorescence from PSI markedly increases. Thermally-induced fluorescence seen in membranes of cyanobacteria showed a high sensitivity to structural and functional membrane alterations induced by pH changes, different electron transport stabilizing agents or different concentrations of MgCl2.     

Effect of formate on Mössbauer parameters of the non-heme iron of PS II particles of cyanobacteria

Mössbauer spectra were measured for PSII particles having an active water-splitting system. The particles were isolated from the thennophilic cyanobacterium Synechococcus elongatus enriched in⁵⁷Fe. The Mössbauer resonance absorption spectrum is a superposition of 3 doublets with the following quadrupole splitting and chemical shift: 1, δ = 0.40, Δ = 0.85; II, δ = 1.35,Δ =2.35; III, δ = 0.25, Δ = 1.65. The δ and Δ values of doublets I, II, III are characteristic of proteins with iron-sulphur center, non-heme iron of the reaction center of higher plants and of the oxidized cytochrome 6–559. Treatment with sodium formate to remove bicarbonate affects only the doublet of non-heme iron, causing its quadrupole splitting to reduce to 1.75 and the chemical shift to reduce to 0.90. After washing out the formate, the Mossbauer spectrum of non-heme iron is restored. The data suggest that bicarbonate is a ligand for the non-heme iron of the reaction center of cyanobacteria.