Birds learn to avoid aposematic prey by using the appearance of host plants

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State-selective modulation of heterotrimeric Gαs signaling with macrocyclic peptides

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Protection by Alcuronium of Muscarinic Receptors Against Chemical Inactivation and Location of the Allosteric Binding Site for Alcuronium

Abstract: We have found earlier that the neuromuscular blocker alcuronium binds to cardiac muscarinic receptors simultaneously with their specific antagonist [³H]methyl- N -scopolamine ([³H]NMS) and allosterically increases their affinity to this ligand. Nothing is known about the allosteric site with which alcuronium interacts. To gain an insight, we have now investigated how the binding of [³H]NMS is affected by agents known to modify specific residues in proteins and how their effects are altered by alcuronium. Reagents that covalently modify the tyrosyl residues ( p -nitrobenzenesulfonyl fluoride and 4-chloro-7-nitrobenzofurazan) and the carboxyl groups of aspartate and glutamate [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N,N' -dicyclohexylcarbodiimide, and N -ethyl-5-phenylisoxazolium-3'-sulfonate] blocked the binding of [³H]NMS to receptors in rat heart atria. Their action was probably due to the modification of tyrosyl and aspartyl residues directly in the muscarinic binding sites because it was antagonized by atropine and carbamoylcholine. Alcuronium and gallamine, another allosteric ligand, also protected the [³H]NMS binding sites against the inactivation by tyrosine- and carboxyl-directed chemical modifiers just as well as by benzilylcholine mustard, known to attach covalently to the muscarinic binding sites. Protection by alcuronium has also been observed on cerebrocortical muscarinic receptors. The effect of alcuronium indicates that the drug interferes with the access of chemical modifiers to the muscarinic sites. In view of the unspecific nature of most of the modifiers used (with regard to muscarinic mechanisms), the protection by alcuronium appears to be best explained on the assumption that the drug binds in close vicinity of the "classical" muscarinic site and sterically blocks the access to this site.     

Chemical and sensory characteristics of the fruits of eight cultivars of field grown tomato

The physical and sensory characteristics of tomato fruits (cf. Gajc-Wolska et al.: Physical and sensory characteristics of the fruits …, this issue) were supplemented by total sugars and titratable acid analysis and flavor. The instrumental and sensory methods were highly statistically correlated. Comparison of cultivars always requires that physical and chemical analysis of tomato fruit quality should always include results of sensory evaluation.     

Pollution by conspecifics as a component of intraspecific competition among Aedes aegypti larvae

Abstract.  1. The role of pollution by conspecifics in the costs associated with larval intraspecific competition was investigated for Aedes aegypti (Diptera: Culicidae).
2. The growth of larval A. aegypti mosquitoes reared in clean water and water in which another larva had previously grown was compared; this procedure eliminates interactions through food consumption between competitors and allows the effects of other processes to be expressed.
3. A cost of growing in polluted water was found: this cost was expressed as an increase in developmental time and a reduction of adult longevity when starved, starved adult dry weight, and wing length.
4. Contrary to previously reported results of an experiment allowing for competition for food, these costs were not expressed in a sex-specific manner and were independent of the sex of the polluter.
5. It was thus demonstrated that competition arises from both resource depletion and other effects that result in deterioration of the environment, with chemical pollution of the environment being the most likely cause.     

The resonance approach to the formation and structure of atoms and molecules

As shown recently, the set of electronic configurations of all chemical elements in the subshell partitioning has a four-dimensional structure. Hence, all elements can be subdivided into cycles and supercycles rather than into periods of the conventional Periodic Table. Moreover, in the plane of the principal and orbital quantum numbers there is an obvious symmetry between the hydrogen-atom spectrum (one-electron problem) and the electronic configurations of all atoms (multi-electron problem). In order to explain these phenomena, it is hypothesized that between shell electrons and nuclei protons there exists a reversible quantum-field interaction (electron + proton ↔ neutron + neutrino resonance). Even if this interaction were a rare event, it can explain the existence of 4D symmetries mentioned above. However, the model considered here is based on frequent epn interactions, taking place more often than 10¹⁵ times per second. In this case, epn resonance and resonance between such resonances are supposed to underlie the structure of all atoms and molecules. In particular, the functioning of all biological molecules, including electron transfer and enzymatic activity, is determined by resonance, resonance between resonances, hierarchy of resonances, and networks of resonances. The text was submittred by the author in english.     

Plant polyphenols—secondary metabolism and chemical defence: Some observations

Secondary metabolism and theories of plant-animal co-evolution are briefly discussed. Current ideas concerning the role of polyphenols as mediators of a general form of chemical defence in plants are outlined. Studies are described of the association of a group of biosynthetically inter-related polyphenols based on gallic acid and D-glucose with the protein bovine serum albumin. The results are interpreted in terms of structure-activity relationships in protein-polyphenol complexation and are used to comment on the co-evolution theory and the position of plant polyphenols in higher plant secondary metabolism and defence.     

Development of Lake Kortowskie in relation to the climatic changes in three Holocene periods

Paleolimnological studies which included analyses of diatoms, plant pigments and physico-chemical characteristics of the bottom sediments have been used to describe the evolution of Lake Kortowskie in three Holocene periods. Characteristic stages of lake development have been distinguished in the Atlantic, Subboreal and Subatlantic periods, these stages differed with respect to the level of production, water level, impact of allochthonic factors and variety of taxonomic composition of the diatoms. It has been shown that Lake Kortowskie was most productive in the Atlantic and the Subatlantic period. On the other hand, the Subboreal period was characterized by a considerable drop of production, most probably caused by strong erosion and worsening climatic conditions. It has been suggested that lake fertility in Atlantic period was probably due to climatic optimum, whereas in the youngest, Subatlantic period the increase of productivity resulted more from internal features of the lake, viz. its age, the time - related increase in the pool of nutrients. The great variety of diatom remains, which increases towards the surface of the sediment profile, confirms the suggestion of generally favourable conditions for lake development as well as its increasing fertility.     

Trajectory analysis of forest canopy effects on chemical flux in throughfall

Short interval sampling of precipitation inputs and stem flow-throughfall (SF-TF) outputs was conducted in a subalpine balsam fir forest to analyze the controls on canopy ion flux. A canopy hydrology model was used to separate the effects of abiotic and biotic processes. The time lag between precipitation inputs and SF-TF outputs caused by the storage of water in the canopy required that time-course patterns of SF-TF flux be examined graphically. The resulting trajectory analyses disclosed patterns from which we generalized about canopy processing of precipitation inputs. Changes in the ion concentration gradient across canopy tissue surfaces appeared to be an important factor in regulating the rate of flux of ions between canopy tissues and SF-TF. These changes were in turn determined by changes in such factors as apoplast ion concentrations and the residence time of water in the canopy. These generalizations permit qualitative predictions of SF-TF flux in other canopies over time based on only rudimentary knowledge of canopy structure and function.     

Inactivation and covalent modification of CTP synthetase by thiourea dioxide.

Thiourea dioxide was used in chemical modification studies to identify functionally important amino acids in Escherichia coli CTP synthetase. Incubation at pH 8.0 in the absence of substrates led to rapid, time dependent, and irreversible inactivation of the enzyme. The second-order rate constant for inactivation was 0.18 M-1 s-1. Inactivation also occurred in the absence of oxygen and in the presence of catalase, thereby ruling out mixed-function oxidation/reduction as the mode of amino acid modification. Saturating concentrations of the substrates ATP and UTP, and the allosteric activator GTP prevented inactivation by thiourea dioxide, whereas saturating concentrations of glutamine (a substrate) did not. The concentration dependence of nucleotide protection revealed cooperative behavior with respect to individual nucleotides and with respect to various combinations of nucleotides. Mixtures of nucleotides afforded greater protection against inactivation than single nucleotides alone, and a combination of the substrates ATP and UTP provided the most protection. The Hill coefficient for nucleotide protection was approximately 2 for ATP, UTP, and GTP. In the presence of 1:1 ratios of ATP:UTP, ATP:GTP, and UTP:GTP, the Hill coefficient was approximately 4 in each case. Fluorescence and circular dichroism measurements indicated that modification by thiourea dioxide causes detectable changes in the structure of the protein. Modification with [14C]thiourea dioxide demonstrated that complete inactivation correlates with incorporation of 3 mol of [14C]thiourea dioxide per mole of CTP synthetase monomer. The specificity of thiourea dioxide for lysine residues indicates that one or more lysines are most likely involved in CTP synthetase activity. The data further indicate that nucleotide binding prevents access to these functionally important residues.