Inhibition of leucyl-tRNA-synthetases by modified ATP analogs

The interaction between modifying ATP analogs containing alkylating or phosphorylating groups in the polyphosphate moiety of the ATP molecule and leucyl-tRNA synthetases from cytoplasm and chloroplasts of Euglena gracilis (strain Z) was studied. It was shown that most of the ATP analogs irreversibly inhibit the cytoplasmic enzyme, having no inhibiting effect on the chloroplast synthetase. The kinetic constants K1 and k2 for the interaction between the most effective irreversible inhibitors and the cytoplasmic enzyme were determined. The data on the protection of the enzyme activity by substrates against irreversible inhibition suggest, that the effect of the adenosine 5'-(beta-chloroethyl phosphate) is directed to the ATP-binding site of the cytoplasmic enzyme, whereas the mixed anhydride of AMP and mesithylene carbonic acid acts predominantly on the binding site of 3'-terminal adenosine of the tRNALeu molecule. ATP analogs may be effectively used for affinity labelling of the cytoplasmic leucyl-tRNA synthetase.     

Chirped dissipative ion-cyclotron solitons in the Earth’s low-altitude ionospheric plasma with two ion species

Conditions for the excitation of small-scale nonlinear ion-cyclotron gradient-drift dissipative structures in cold ionospheric plasma are considered. The solution for the wave electric field in this structure in the form of a chirped soliton satisfying the equation of the Ginzburg-Landau type is derived in the electrostatic approach. The dissipative structure as a whole represents the chirped soliton accompanied by the comoving quasineutral plasma hump. The possibility of the excitation of two modes of this type (the high- and low-frequency ones) in plasma containing light and heavy ion impurities is considered. The role of electromagnetic corrections and the possible contribution introduced by these structures to the transport processes in the ionosphere are discussed.     

European checkerspots (Melitaeini: Lepidoptera,Nymphalidae) are not aposematic – the point of view of great tits (Parus major)

相似文献   

A GHF7 CELLULASE FROM THE PROTIST SYMBIONT COMMUNITY OF Reticulitermes flavipes ENABLES MORE EFFICIENT LIGNOCELLULOSE PROCESSING BY HOST ENZYMES

Termites and their gut microbial symbionts efficiently degrade lignocellulose into fermentable monosaccharides. This study examined three glycosyl hydrolase family 7 (GHF7) cellulases from protist symbionts of the termite Reticulitermes flavipes. We tested the hypotheses that three GHF7 cellulases (GHF7‐3, GHF7‐5, and GHF7‐6) can function synergistically with three host digestive enzymes and a fungal cellulase preparation. Full‐length cDNA sequences of the three GHF7s were assembled and their protist origins confirmed through a combination of quantitative PCR and cellobiohydrolase (CBH) activity assays. Recombinant versions of the three GHF7s were generated using a baculovirus‐insect expression system and their activity toward several model substrates compared with and without metallic cofactors. GHF7‐3 was the most active of the three cellulases; it exhibited a combination of CBH, endoglucanase (EGase), and β‐glucosidase activities that were optimal around pH 7 and 30°C, and enhanced by calcium chloride and zinc sulfate. Lignocellulose saccharification assays were then done using various combinations of the three GHF7s along with a host EGase (Cell‐1), beta‐glucosidase (β‐glu), and laccase (LacA). GHF7‐3 was the only GHF7 to enhance glucose release by Cell‐1 and β‐glu. Finally, GHF7‐3, Cell‐1, and β‐glu were individually tested with a commercial fungal cellulase preparation in lignocellulose saccharification assays, but only β‐glu appreciably enhanced glucose release. Our hypothesis that protist GHF7 cellulases are capable of synergistic interactions with host termite digestive enzymes is supported only in the case of GHF7‐3. These findings suggest that not all protist cellulases will enhance saccharification by cocktails of other termite or fungal lignocellulases.     

Complexes of antiparallel telomeric G-quadruplex d(TTAGGG)4 with carboxymethyl tetracationic porphyrins

Porphyrins are a chemical class that is widely used in drug design. Cationic porphyrins may bind to DNA guanine quadruplexes. We report the parameters of the binding of 5,10,15,20-tetrakis(N-carboxymethyl-4-pyridinium) porphyrin (P1) and 5,10,15,20-tetrakis(N-etoxycarbonylmethyl-4-pyridinium) porphyrin (P2) to antiparallel telomeric G-quadruplex formed by d(TTAGGG)₄ sequence (TelQ). The binding constants (K _i ) and the number of binding sites (N _j ) were determined from absorption isotherms generated from the absorption spectra of complexes of P1 and P2 with TelQ. Compound P1 demonstrated a high affinity to TelQ (K _i = (40 ± 6) × 10⁶ M^?1, N ₁ = 1; K ₂ = (5.4 ± 0.4) × 10⁶ M^?1, N ₂ = 2). In contrast, the binding constants of P2-TelQ complexes (K ₁ = (3.1 ± 0.2) × 10⁶ M^?1, N ₁ = 1; K ₂ = (1.2 ± 0.2) × 10⁶ M^?1, N ₂ = 2) were one order of magnitude smaller than the corresponding values for P2-TelQ complexes. Measurements of the quantum yield and fluorescence lifetime of the drug’s TelQ complexes revealed two types of binding sites for P1 and P2 on the quadruplex oligonucleotide. We concluded that strong complexes can result from the interaction of the porphyrins with TTA loops whereas the weaker complexes are formed with G-quartets. The altered TelQ conformation detected by the circular dichroism spectra of P1-TelQ complexes can be explained by the disruption of the G-quartet. We conclude that peripheral carboxy groups contribute to the high affinity of P1 for the antiparallel telomeric G-quadruplex.     

Cytogenetic effects in peripheral blood lymphocytes in descendants of chernobyl disaster liquidators under the impact of mitomycin c in vitro and folic acid in vivo

Data on cytogenetic examinations of the descendans of Chernobyl disaster liquidators (cleanup personnel) have been obtained. It has been established that the level of spontaneous chromosomal aberrations before folic acid administration was 1.8 times higher than that value after its employment (4.45 vs 2.42%, p < 0.01). In lymphocyte cultures treated with mitomycin C accompanied by folic acid, it was 4.5 times higher before their administration (23.95 vs 5.36%, p < 0.001). The data obtained confirm the possibility of stabilizing the genetic apparatus in the descendans of Chernobyl disaster liquidators after folic acid administration.     

The t-SNARE AtVAM3p resides on the prevacuolar compartment in Arabidopsis root cells

Protein cargo is trafficked between the organelles of the endomembrane system inside transport vesicles, a process mediated by integral membrane proteins called SNAREs (soluble N-ethylmaleimide sensitive factor attachment protein receptors) that reside on the surface of the vesicle (v-SNAREs) and target membrane (t-SNAREs). In examining transport of cargo between the trans-Golgi network and the vacuole in Arabidopsis, we have previously characterized AtPEP12p as a t-SNARE residing on the prevacuolar compartment and AtVTI1a as a v-SNARE that interacts with AtPEP12p. Recently, we have begun to characterize AtVAM3p, another Arabidopsis t-SNARE that shows high sequence homology to AtPEP12p. We have found that AtVTI1a also interacts with AtVAM3p, suggesting a role for this t-SNARE in post-Golgi trafficking. AtVAM3p has been suggested to localize to the vacuolar membrane in Arabidopsis cells; however, using specific antisera and expression of epitope-tagged versions of each t-SNARE, we have discovered that AtVAM3p is found on the same prevacuolar structure as AtPEP12p in Arabidopsis root cells.     

Can foreign proteins imported into yeast mitochondria interfere with PIM1p protease and/or chaperone function?

When studying the fate of mammalian apocytochrome P450scc (apo-P450scc) imported in small amounts into isolated yeast mitochondria, we found that it undergoes degradation, this process being retarded if recipient mitochondria are preloaded in vivo (to about 0.2% of total organelle protein) with a fusion protein composed of mammalian adrenodoxin reductase and adrenodoxin (AdR-Ad); in parallel we observed aggregation of apo-P450scc. These effects suggest some overload of Pim1p protease and/or mtHsp70 system by AdR-Ad, as both of them are involved in the degradation of apo-P450scc (see Savel'ev et al. J. Biol. Chem. 273, 20596-20602, 1998). However, under the same conditions AdR-Ad was not able to impede the import of proteins into mitochondria and the development of the mitochondrial respiratory machinery in yeast, the processes requiring the mtHsp70 system and Pim1p, respectively. These data imply that chaperones and Pim1p protease prefer their natural targets in mitochondria to imported foreign proteins.     

Antiesterase activity and toxicity of O,O-dialkyl-S-ethoxycarbonylbromomethylthiophosphates

The interaction of potential pesticides, O,O-dialkyl S-ethoxycarbonylbromomethylthiophosphates (RO)2P(O)SCH(Br)COOC2H5 (R = Et, i-Pr, n-Pr, n-Bu, n-Am, or n-Hx) with the esterases of warm-blooded animals [acetylcholinesterase (ACE), butyryl cholinesterase (BCE), and carboxyl esterase (CE)] was studied. The acute toxicities of these compounds for mice were determined. All the compounds were non-hydrolyzable by CE and capable of irreversible inhibition of all these esterases with ki (M-1 min-1) of 1.2 x 10(5)-6 x 10(6), 2.0 x 10(6)-1.5 x 10(8), and 2.0 x 10(8), respectively. By using multiple regression analysis, we found that the steric factor plays a significant role in the inhibition of ACE, with the steric hindrances manifesting themselves even at the sorption stage. On the other hand, hydrophobic interactions predominate in the case of BCE, while steric properties of its substituents exert a markedly weaker effect and manifest themselves at the phosphorylation stage. We suggested the presence of an electrophilic region in the active site of ACE, which can interact with the ethoxycarbonyl group of the thiophosphates under study. The decrease in toxicities and the affinities to BCE and CE were found to correlate with an increase in the length of n-alkyl substituents of the compounds studied. This suggests that the unspecific esterases play a significant role as a buffer system in the exhibition of toxic effects by the thiophosphates under consideration.     

Sex ratio in Down syndrome

Data from 55 publications providing the sex ratio (SR), i.e. ratio between male and female cases of Down syndrome (DS), are presented. In general, SR was skewed toward an excess of males in the majority of studied populations, either in populations with a high level of cases ascertainment (epidemiological studies) or in selected groups. No significant correlation involving the age of either patients or mothers was found. Some other factors which might influence the sex ratio in DS at birth are mentioned. Meta-analysis of data from epidemiological studies suggests the phenomenon is not restricted to free trisomy 21 alone but appears in translocation cases, both in mutant and inherited translocation carriers (SR = 1.31 and 1.36, respectively). In contrast to nonmosaic 47, +21 cases, where SR is close to 1.3, an excess of females was observed in mosaics 46/47, +21 (SR = 0.83). No male predominance was found among patients with DS not tested cytogenetically (SR = 0.98), which may be explained by female predominance in false-positive cases. In populations with a fraction of clinically diagnosed cases of 30% and over, SR has intermediate value of 1.1. The ratio showed a tendency to increase since 1940's, reaching a mean value of 1.35 in 1980's varying from 1.3 to 1.62 in different populations), which might be a consequence of the growing use of karyotyping to confirm diagnosis and of a real increase in proportion of males. In the 1990's, the ratio fell to 1.22 varying from 1.03 to 1.27. As SR is assumed to reflect a proportion of paternal contribution, the discrepancy between the proportions of paternal errors in cytogenetic studies on parental origin of the extra chromosome (24% in the 1980's) and in molecular studies (5-10% in the 1990's) discussed in the literature might be explained by temporal changes alone. Genetic mechanisms of male predominance in trisomy 21 are reviewed, among them models for joint segregation of chromosome 21 and Y chromosome in spermatogenesis, and the chromosome 21 nondisjunction during 2nd meiotic division of oogenesis caused by Y chromosome-bearing spermatozoa.