The oxidizing side of photosystem 2 (PS2) contains a set of unique redox components including two tyrosine radicals, Tyr2 and Tyrp, and a cluster of 4 Mn atoms that are involved in the oxidation of water to molecular oxygen. The structural environment of these components is unknown; we ušed computer-assisted modelling to create a three-dimensional model for the structure around Tyr^ and Tyrj). The tyrosines are predicted to be located in hydrophobic cavities in the Dl and D2 reaction centre proteins, respectively. The cavities are situated close to the lumenal surface of the thylakoid membrane and are surrounded mainly by highly conserved amino acid residues. Both tyrosines are proposed to be hydrogen-bonded to the nearby histidine residues Hisl90 on respective protein. We tested the model by electron paramagnetic resonance (EPR) spectroscopy of Tyr^ and site-directed mutagenesis of the D2 protein in the cyanobacterium Synechocystis 6803. In two mutants, where the corresponding histidine is changed to a tyrosine or a leucine, the normál EPR spectra from Tyr^ were drastically altered to narrow structureless radical signals with g-values similar to that of Tyrp (g » 2.0050). The new spectra were assigned to Tyrp from functional experiments and the spectral modification indicated that the introduced point-mutation of His 190 (D2-Hisl89 in Synechocystis 6803) modified the environment around Tyr^ supporting the structural model. In a third mutant where Glnl65 (D2-Glnl64 in Synechocystis 6803) was exchanged to a leucine we also observed a modified EPR spectrum consistent with the predictions firom the model. AU the experimental data obtained strengthen the Computer derived model in essential aspects. We also predicted a possible location for the Mn-cluster to the loop that connects the membrane spanning helices A and B on the Dl protein. In addition the structural model suggests the presence of a metal-site, possibly a Mn site, close to Tyrz on the Dl protein. The site is proposed to be constituted of three residues on the Dl protein, Glnl65, Aspl70 and Glul89.
Phoridae (scuttle flies) are widely distributed, occur in many types of habitats and are ecologically versatile, which makes them an excellent bioindicator group for evaluating faunal diversity. The structure of scuttle fly communities was compared in two Mediterranean habitats in the Montseny Natural Park (Catalonia, Spain) that differ in vegetation and microclimate: beech forest and highland scrubland. 3684 male individuals belonging to 135 species of scuttle flies were identified. Scuttle flies were more abundant in beech forest than scrubland. Observed and estimated species richness were lower in scrubland than in beech forest, while diversity was similar in both habitats. Community evenness was greater in scrubland than beech forest. Therefore, the percentage of dominant and subdominant species was higher in scrubland than beech forest, while the percentage of rare species was higher in beech forest than scrubland. Scuttle fly species composition was significantly different in the two habitats, but it was similar among plots within the same habitat. Megaselia pectoralis (Wood, 1910) and Megaselia subpleuralis (Wood, 1909) were the dominant species in beech forest, while Megaselia pusilla (Meigen, 1830), Megaselia pumila (Meigen, 1830), Megaselia superciliata (Wood, 1910) and Megaselia diversa (Wood, 1909) were the dominant species in scrubland. Trophic specialization was higher in beech forest than scrubland. Saprophages were the dominant trophic group in beech forest, while fungivores and polyphages were dominant in scrubland. The high biodiversity of scuttle flies recorded in the Montseny Natural Park indicates that there is also a high diversity of other taxa there and that these Mediterranean mountains are of high conservation status., Carlos García-Romera, José A. Barrientos., and Obsahuje bibliografii
We studied the agamic complex of Hieracium subgen. Pilosella in the Šumava/Böhmerwald, the borderland between the Czech Republic and Germany. Their DNA ploidy levels/chromosome numbers, breeding systems, chloroplast haplotypes as well as the clonal structure of apomicts were determined. The complex consists of the following basic and intermediate species and recent hybrids. Basic species: H. aurantiacum L. (tetraploid and pentaploid, both apomictic), H. caespitosum Dumort. (tetraploid, apomictic), H. lactucella Wallr. (diploid, sexual), H. pilosella L. (tetraploid, sexual); intermediate species: H. floribundum Wimm. et Grab. (tetraploid, apomictic), H. glomeratum Froel. (tetraploid and pentaploid, both apomictic), H. scandinavicum Dahlst. (tetraploid, apomictic); recent hybrids: H. floribundum × H. pilosella (partly corresponding to H. piloselliflorum – tetraploid and hexaploid; tetraploid sexual or apomictic), H. glomeratum × H.pilosella (aneuploid, 2n = 38), H. aurantiacum × H. floribundum (tetraploid, almost sterile or apomictic), H. lactucella × H. pilosella (H. schultesii, triploid sterile, tetraploid sexual), H. aurantiacum × H. pilosella (H. stoloniflorum, tetraploid, sexual), H. aurantiacum > H. pilosella (H. rubrum, hexaploid). The hexaploid hybrids between H. pilosella and H. floribundum or H. aurantiacum produced mainly polyhaploid progeny. Two trihaploid plants were found growing in the neighbourhood of their putative hexaploid maternal parent H. rubrum, which is the first record of polyhaploids of this subgenus in the field. Comparison with other mountain ranges (especially the Krušné hory/Erzgebirge, and Krkonoše) with an almost identical composition of basic species, revealed that the structure of the agamic complexes differ.
Scanning electron microscopy of the cystidicolid nematode Ascarophis mexicana Moravec, Salgado-Maldonado et Vivas-Rodríguez, 1995 enabled the first detailed study of its cephalic structure. In contrast to most Ascarophis species, its pseudolabia are highly reduced and sublabia are unlobed and weakly developed. Similascarophis is considered a synonym of Ascarophis, to which two its species are transferred as A. maulensis (Muñoz, González et George-Nascimento, 2004) comb. n. and A. chilensis (Muñoz, González et George-Nascimento, 2004) comb. n.
The cuticle of Rhysotritia duplicita (Euphtiracaroidea: Euphtiracaridae), Phthiracarus sp., Steganacarus magnus, S. striculus and Tropacarus carinatus (all Phthiracaroidea: Phthiracaridae) was studied by light and transmission electron microscopy. A combination of light and electron microscopy were used to precisely characterize and classify the cuticular layers in oribatid mites and show how they differe in mites and other arthropods. In Rhysotritia duplicata the cuticle of the aspis (upper shield of the prosoma) differs significantly from that of the opisthosoma. Moreover, prosomal cuticle in this species is different from that of all others species studied. There were no structural differences in the cuticle of the prosoma and opisthosoma of species of the superfamily Phthiracaroidea (Phthiracarus, Steganacarus and Tropacarus) in spite of the differences in external apparence. Moreover, in Tropacarus, the rough sculpturing of the cuticle results from the very rough exocuticle, which is unlike the thick smooth cerotegument of the cuticle in Steganacarus.
Scanning electron microscopy (SEM) examination of a paratype specimen (gravid female) of the philometrid nematode Paraphilometroides nemipteri Moravec et Shaharom-Harrison, 1989, the type species of Paraphilometroides Moravec et Shaharom-Harrison, 1989, made it possible to recognise the true structure of the cephalic end and the shape of cuticular ornamentations on the body. In contrast to other philometrid genera, the cephalic end is angular in lateral view and rounded in dorsoventral view; large external cephalic papillae are fused together to form a marked dorsal and a ventral ala, each bent into a curve; six minute internal papillae, including a pair of previously not reported lateral papillae, were found; amphids were indistinct. Cuticular ornamentations (inflations) were found to be transversely elongated. These features, especially the unique cephalic structure, clearly distinguish Paraphilometroides from other philometrids and confirm the validity of this genus.
Various instruments were used to observe the solar corona and prominences near or at the time of solar eclipse, 22 July 1990. The white-light solar corona pictures were observed nearly up to R = 3 (solar radii) with the Úpice Observatory eclipse team at Markovo. Both emission line intensities (the green and red corona) and prominences were obtained at Lomnický Peak coronal station. These data sets are used to identify active coronal regions. A large coronal hole was observed above the south pole and extending nearly up to R = 2.5. Large-scale structure of the white-light corona is very complicated. There are many streamers nearly equally distributed around the whole Sun (except the south pole). Several streamers above the solar surface are not extended radially with
their height. In the NE quadrant 4 voids are clearly seen at the height of about R = 2. A slight excess of the white light corona is in favor of the west limb, however, the emission corona has an opposite meaning. Green and red corona, similarly as prominences, showed rapid changes in active regions over the eclipse period, however, any CME was not directly observed. The integral brightness of the 22 July 1990 white-light corona was estimated as JK = 1.32 x 10~6 and the ellipticity, a + b = 0.04. The white-light corona was nearly a maximum type.
In this paper, we determine all the normal forms of Hermitian matrices over finite group rings $R=F_{q^2}G$, where $q=p^{\alpha }$, $G$ is a commutative $p$-group with order $p^{\beta }$. Furthermore, using the normal forms of Hermitian matrices, we study the structure of unitary group over $R$ through investigating its BN-pair and order. As an application, we construct a Cartesian authentication code and compute its size parameters.
The structure of the vertebrate predator community in north-eastern Belarus has been examined before and after naturalization of the American mink and raccoon dog. Species composition of the community, population density and biomass, portion of each species in the pooled community density and biomass, species body mass and size structure of the community were investigated. The community consisted of 36 native predator species, and 11 other predator species were sporadically registered in the area in both periods before the American mink and raccoon dog expansion and after the introduced species have reached a high population density. Separating predator species into four size groups, we found that in terms of total density the largest portion of the community belonged to small predators, while large predators formed the smallest portion. In terms of total biomass, the larger medium-sized predator group predominated over other size groups. Despite decline in the populations of ten native predator species, the total community density and biomass as well as portions of different size groups appeared to be very similar before and after naturalization of the introduced predator species.
NMDA receptors have received much attention over the last few decades, due to their role in many types of neural plasticity on the one hand, and their involvement in excitotoxicity on the other hand. There is great interest in developing clinically relevant NMDA receptor antagonists that would block excitotoxic NMDA receptor activation, without interfering with NMDA receptor function needed for normal synaptic transmission and plasticity. This review summarizes current understanding of the structure of NMDA receptors and the mechanisms of NMDA receptor activation and modulation, with special attention given to data describing the properties of various types of NMDA receptor inhibition. Our recent analyses point to certain neurosteroids as NMDA receptor inhibitors with desirable properties. Specifically, these compounds show use-dependent but voltage-independent block, that is predicted to preferentially target excessive tonic NMDA receptor activation. Importantly, neurosteroids are also characterized by use-independent unblock, compatible with minimal disruption of normal synaptic transmission. Thus, neurosteroids are a promising class of NMDA receptor modulators that may lead to the development of neuroprotective drugs with optimal therapeutic profiles., V. Vyklicky ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy