Hydrogenases and Hydrogen Metabolism of Cyanobacteria

Cyanobacteria may possess several enzymes that are directly involved in dihydrogen metabolism: nitrogenase(s) catalyzing the production of hydrogen concomitantly with the reduction of dinitrogen to ammonia, an uptake hydrogenase (encoded by hupSL) catalyzing the consumption of hydrogen produced by the nitrogenase, and a bidirectional hydrogenase (encoded by hoxFUYH) which has the capacity to both take up and produce hydrogen. This review summarizes our knowledge about cyanobacterial hydrogenases, focusing on recent progress since the first molecular information was published in 1995. It presents the molecular knowledge about cyanobacterial hupSL and hoxFUYH, their corresponding gene products, and their accessory genes before finishing with an applied aspect—the use of cyanobacteria in a biological, renewable production of the future energy carrier molecular hydrogen. In addition to scientific publications, information from three cyanobacterial genomes, the unicellular Synechocystis strain PCC 6803 and the filamentous heterocystous Anabaena strain PCC 7120 and Nostoc punctiforme (PCC 73102/ATCC 29133) is included.     

Effect of dimethyl sulfoxide on the structure and the functional properties of horseradish peroxidase as observed by spectroscopy and cyclic voltammetry

Electrochemical biosensors have found wide application in food and clinical areas, as well as in environmental field. A large number of articles focused on horseradish peroxidase (HRP)-based biosensors have been published in the last decade, due to the capability of HRP to quantitatively detect the presence of hydrogen peroxide produced in a reaction. At present a large body of multi-enzymatic amperometric biosensors are realized by entrapping HRP together with other enzymes into a polymeric matrix; these systems represent a promising example of simple, low-cost electrochemical tools for the analysis of bioanalytes in solution, such as glucose, choline and cholesterol. Due to the fact that polymers used for HRP entrapping are soluble in organic solvents and that many solvents are strong denaturants of aquo-soluble proteins, in this paper we investigate (in particular, by circular dichroism and electron paramagnetic spectroscopies) the effect of dimethyl sulfoxide, one of the organic solvents employed for polymer solubilization, on the structure and the functionality of HRP, in order to determine the effect induced by the solvent concentration on the structure and activity of the hemoprotein. This is relevant for basic and applied biochemistry, HRP being largely employed in bioinorganic chemistry and sensor area.     

A cladistic analysis ofAnisopappus (Asteraceae: Inuleae)

A cladistic analysis of the genusAnisopappus (Asteraceae: Inuleae) has been undertaken. A hypothesis of species interrelationships in the genus is presented for the first time. The analysis also includedArctotis (Arctoteae), used as outgroup, and five additional genera from theInuleae: Geigeria, Calostephane, Asteriscus, Buphthalmum, Pulicaria, andInula. It is concluded thatAnisopappus is a monophyletic group situated at the base of the tribe, diagnosed by, e.g., their obtuse stylar sweeping-hairs. The species with acute sweeping-hairs were found to be derived within the genus. Problems concerning species delimitation, biogeography and character evolution in the genus are briefly discussed.     

Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.     

The TORNADO1 and TORNADO2 genes function in several patterning processes during early leaf development in Arabidopsis thaliana

In multicellular organisms, patterning is a process that generates axes in the primary body plan, creates domains upon organ formation, and finally leads to differentiation into tissues and cell types. We identified the Arabidopsis thaliana TORNADO1 (TRN1) and TRN2 genes and their role in leaf patterning processes such as lamina venation, symmetry, and lateral growth. In trn mutants, the leaf venation network had a severely reduced complexity: incomplete loops, no tertiary or quaternary veins, and vascular islands. The leaf laminas were asymmetric and narrow because of a severely reduced cell number. We postulate that the imbalance between cell proliferation and cell differentiation and the altered auxin distribution in both trn mutants cause asymmetric leaf growth and aberrant venation patterning. TRN1 and TRN2 were epistatic to ASYMMETRIC LEAVES1 with respect to leaf asymmetry, consistent with their expression in the shoot apical meristem and leaf primordia. TRN1 codes for a large plant-specific protein with conserved domains also found in a variety of signaling proteins, whereas TRN2 encodes a transmembrane protein of the tetraspanin family whose phylogenetic tree is presented. Double mutant analysis showed that TRN1 and TRN2 act in the same pathway.     

Structural investigation of disordered stress proteins. Comparison of full-length dehydrins with isolated peptides of their conserved segments

Dehydrins constitute a class of intrinsically disordered proteins that are expressed under conditions of water-related stress. Characteristic of the dehydrins are some highly conserved stretches of seven to 17 residues that are repetitively scattered in their sequences, the K-, S-, Y-, and Lys-rich segments. In this study, we investigate the putative role of these segments in promoting structure. The analysis is based on comparative analysis of four full-length dehydrins from Arabidopsis (Arabidopsis thaliana; Cor47, Lti29, Lti30, and Rab18) and isolated peptide mimics of the K-, Y-, and Lys-rich segments. In physiological buffer, the circular dichroism spectra of the full-length dehydrins reveal overall disordered structures with a variable content of poly-Pro helices, a type of elongated secondary structure relying on bridging water molecules. Similar disordered structures are observed for the isolated peptides of the conserved segments. Interestingly, neither the full-length dehydrins nor their conserved segments are able to adopt specific structure in response to altered temperature, one of the factors that regulate their expression in vivo. There is also no structural response to the addition of metal ions, increased protein concentration, or the protein-stabilizing salt Na(2)SO(4). Taken together, these observations indicate that the dehydrins are not in equilibrium with high-energy folded structures. The result suggests that the dehydrins are highly evolved proteins, selected to maintain high configurational flexibility and to resist unspecific collapse and aggregation. The role of the conserved segments is thus not to promote tertiary structure, but to exert their biological function more locally upon interaction with specific biological targets, for example, by acting as beads on a string for specific recognition, interaction with membranes, or intermolecular scaffolding. In this perspective, it is notable that the Lys-rich segment in Cor47 and Lti29 shows sequence similarity with the animal chaperone HSP90.     

Competition and facilitation within and between a snail and a mayfly larva and the effect on the grazing process

We studied the competitive effects within and between two taxonomically distant freshwater herbivores, a snail and a mayfly, common in Swedish lakes, Lymnaea peregra and Cloeon dipterum, respectively, and their effect on grazing in a laboratory experiment. The experimental set-up consisted of 2-l aquaria, each containing a periphyton covered tile. Intra- and interspecific effects were tested by increasing the density of one species at a time in four different treatments, (1) snails (intraspecific treatment), (2) mayflies (intraspecific treatment), (3) mixed-snails (interspecific treatments, snails kept constant) and (4) mixed-mayflies (interspecific treatments, mayflies kept constant). Intraspecific competition affected both snails and mayflies negatively, i.e. increasing mortality with increasing con-specific density. Furthermore, there was a decrease in snail growth with increasing snail density. In the mixed-species treatments both species changed their microhabitat use indicating interspecific competition. Despite this, we also found a positive effect of mayfly density on snail growth, most likely due to indirect commensalism. No density-dependent effect of grazing on periphyton was found, probably due to interference competition between grazers. However, there was a significant difference in periphyton biomass, due to species composition of grazers. Irrespective of their densities, if they co-existed, the two grazer species decreased the periphyton biomass significantly compared with both single-species treatments. We considered this as a joint action of facilitation and interaction. Our results suggest that competition can be an important structuring factor in macroinvertebrate communities and that species composition can be significant for ecosystem processes within lentic environments.     

Smooth Pursuit Eye Movements in Children with Strabismus and in Children with Vergence Deficits

Purpose

The objective of our study was to examine horizontal smooth pursuit performance in strabismic children and in children with vergence deficits, and to compare these data with those recorded in a group of control age-matched children.

Methods

Binocular eye movements were recorded by video-oculography in ten strabismic children (mean age: 9.8±0.8) and seven children with vergence deficits (mean age: 10.8±0.6). Data were compared to that of age-matched control children (mean age: 9.8±0.8 years).

Results

Catch-up saccades amplitude in strabismic children and in children with vergence deficits were significantly higher than in control age-matched children. Moreover, in strabismic children the amplitude of catch-up saccades was significantly higher in rightward than in leftward direction. The number of catch-up saccades was also significantly higher in rightward than in leftward direction. The gain value of pursuits in rightward direction was significantly higher in the right eye than in the left one; for the right eye, the gain value was significantly higher in rightward than in leftward direction. Binocular coordination of pursuit was better in control age-matched children than in children with vergence deficits and than in strabismic children.

Conclusions

Binocular coordination of pursuit is abnormal in children with vergence deficits and worse in strabismic children. Binocular vision plays an important role in improving binocular coordination of pursuit.     

Evaluation of the Antioxidant Properties of Propofol and its Nitrosoderivative. Comparison with Homologue Substituted Phenols

Propofol (2,6-diisopropylphenol), some substituted phenols (2,6-dimethylphenol and 2,6-ditertbutylphenol) and their 4-nitrosoderivatives have been compared for their scavenging ability towards 1,1-diphenyl-2-picrylhydrazyl and for their inhibitory action on lipid peroxidation. These products were also compared to the classical antioxidants butylated hydroxytoluene and butylated hydroxyanisole. When measuring the reactivity of the various phenolic derivatives with 1,1-diphenyl-2-picrylhydrazyl the following order of effectiveness was observed: butylated hydroxyanisole>propofol>2,6-dimethylphenol>2,6-di-tertbutylphenol?>?butylated hydroxytoluene. In cumene hydroperoxide-dependent microsomal lipid peroxidation, propofol acts as the most effective antioxidant, while butylated hydroxyanisole, 2,6-di-tertbutylphenol and butylated hydroxytoluene exhibit a rather similar effect, although lower than propofol. In the iron/ascorbate-dependent lipid peroxidation propofol, at concentrations higher than 10?μM, exhibits antioxidant properties comparable to those of butylated hydroxytoluene and butylated hydroxyanisole. 2,6-Dimethylphenol is scarcely effective in both lipoperoxidative systems. The antioxidant properties of the various molecules depend on their hydrophobic characteristics and on the steric and electronic effects of their substituents. However, the introduction of the nitroso group in the 4-position almost completely removes the antioxidant properties of the examined compounds. The nitrosation of the aromatic ring of antioxidant molecules and the consequent loss of antioxidant capacity can be considered a condition potentially occurring in vivo since nitric oxide and its derivatives are continuously formed in biological systems.