Structure and floristic composition of the Heard Island “pool complex” community

Summary The stratigraphy, hydrology and vegetation of the Heard Island (sub-Antarctic; 53°05S, 73°30E) pool complex bogs are described. Spatial variation in processes that might have contributed to their formation are discussed. This community occurs where drainage is impeded. with Callitriche antarctica being the indicator species. Particular attention is paid to the interaction of the vegetation, pools and animals. Surface stratigraphy, peat depth, water depth and vegetation composition were measured along transect lines. Species cover abundance data of 300 quadrats were classified using a two-way indicator species analysis program and ordinated using detrended correspondence analysis. The major factors determining vegetation composition were found to be peat depth, surface topography, and the degree and type of animal disturbance. Similarities between the pool complexes on Heard Island and corresponding bogs in Tasmania, and the northern hemisphere temperate and boreal zones appear to diminish as the density of the animals occupying this habitat increases.     

Computer simulation of the influence of hydrogen on stress–order correlations in amorphous silicon

This paper reports the computational simulation of the correlations between atomic-level stress and local structure fluctuations in a computational model of amorphous silicon. A single parameter has been identified, which uniquely characterises the structural order in these structures. This parameter is the linear combination of the SDs of the first and second nearest neighbour separations. The stress fluctuations, under progressive hydrogen incorporation, show two clear dependences on this parameter, and therefore on the structural order. This dual dependency clearly alludes to structural network configurations that contain low and high hydrogen concentrations. The implications of the results on the local geometry of tetrahedrally bonded amorphous solids are discussed.     

A Monte–Carlo step-by-step simulation code of the non-homogeneous chemistry of the radiolysis of water and aqueous solutions. Part I: theoretical framework and implementation

The importance of the radiolysis of water in irradiation of biological systems has motivated considerable theoretical and experimental work in the radiation chemistry of water and aqueous solutions. In particular, Monte–Carlo simulations of radiation track structure and non-homogeneous chemistry have greatly contributed to the understanding of experimental results in radiation chemistry of heavy ions. Actually, most simulations of the non-homogeneous chemistry are done using the Independent Reaction Time (IRT) method, a very fast technique. The main limitation of the IRT method is that the positions of the radiolytic species are not calculated as a function of time, which is needed to simulate the irradiation of more complex systems. Step-by-step (SBS) methods, which are able to provide such information, have been used only sparsely because these are time consuming in terms of calculation. Recent improvements in computer performance now allow the regular use of the SBS method in radiation chemistry. In the present paper, the first of a series of two, the SBS method is reviewed in detail. To these ends, simulation of diffusion of particles and chemical reactions in aqueous solutions is reviewed, and implementation of the program is discussed. Simulation of model systems is then performed to validate the adequacy of stepwise diffusion and reaction schemes. In the second paper, radiochemical yields of simulated radiation tracks calculated by the SBS program in different conditions of LET, pH, and temperature are compared with results from the IRT program and experimental data.     

Molecular dynamics simulation of the gGAPDH–NAD+ complex from Trypanosoma cruzi

A 50-ns molecular dynamics simulation has been used to study the homotetramer of the enzyme glycosomal glyceraldehyde 3-phosphate dehydrogenase (gGAPDH) complexes, from Trypanosoma cruzi, with nicotinamide adenine dinucleotide (NAD⁺) cofactors in aqueous solution. The root mean square deviation indicates that the overall structure of the homotetramer does not undergo significant change. The largest structural change observed was in the NAD⁺ binding domain of subunit (chain) D; as a consequence, the NAD⁺ cofactor was dislocated from its initial position. However, the other subunits were not affected, suggesting that the gGAPDH enzyme exhibits non-cooperative behaviour. Our simulation estimates that the NAD⁺ binding domain rotates about 4.8° relative to the catalytic domain in the apo–holo form transition. The hydrogen bond analysis reveals that the residues R12, I13, D38 and M39 are essential for gGAPDH–NAD⁺ interaction. Furthermore, two promising cavities to be explored in drug design were found: one formed by residues I13, R12, T197, T199, E336 and Y339, and the other by residues C166, H194, R249, I13, R12, T197, T199, E336 and Y339. The results presented in this paper offer new insight into the search for inhibitors of the gGAPDH enzyme of T. cruzi protozoan.     

The transformation of the cytoplasmic oestradiol–receptor complex into the nuclear complex in a uterine cell-free system

Experiments performed with a cell-free system in tris-EDTA buffer, pH 7.4, indicate that the high-speed supernatant fraction of the rat uterus contains all the factors necessary to transform the 8S cytoplasmic oestradiol-receptor complex to the nuclear complex. The transformation is temperature-dependent. This nuclear complex was extracted in the form of a 5S particle with 0.4m-KCl from sediments of either uterine or heart nuclei that had been incubated together with the cytoplasmic soluble fraction of the uterus at 2 degrees C for 30min. This complex can also be obtained similarly from the soluble fraction of the uterus, incubated in the absence of nuclei. Previous warming of the soluble fraction to 37 degrees C for 7min was necessary for the successful extraction of the nuclear particle under these conditions of incubation. After an incubation of the transformed complex with the nuclear sediment at 37 degrees C for 7min, the 5S complex was extractable from the uterine nuclear sediment but not from the heart nuclear sediment, which may indicate the tissue specificity of the nuclear acceptor sites for the transformed complex. The extracted uterine nuclear complex sediments in the 5S region, but whether it is the native complex or a subunit or other part of the native complex resulting from the extraction with salt is unknown.     

Prediction and Computer Analysis of the Exon–Intron Structure of Human Genes

This review of the original works on computer analysis of the human genome considers (i) the development of methods to predict the exon–intron structure of genes and (ii) analysis of alternative splicing. Prediction of the gene structure is based on homology between the gene product and a known protein or between the genomic sequences of the gene and its homolog from another organism. The methods were tested and proved highly efficient. Human gene splicing was analyzed with original methods and EST databases. Genes with alternative splicing were for the first time shown to account for no less than 35% of total genes. Alternative splicing was compared for the human and mouse genomes. Species-specific isoforms were demonstrated for 50% of alternatively spliced genes (25% of total genes).     

Populational analysis of thermal responses—I. Changes in the heat resistance of muscle tissue and contractile muscle models of Salamandra salamandra larvae

• 1.1.|Study has been made of the heat resistance of m. rectus superficialis and their contractile models of larvae of 12 families of Salamandra salamandra kept at three different temperatures: 14, 21 (optimal) and 27°C. The heat resistance of the organism has been studied only in larvae kept at 21°C.
• 2.2.|An inverse linear relation has been found between the level of the average heat resistance of muscles for offspring, of the same family, under optimal conditions and its increase caused by a change in environmental temperature. A similar relationship was observed in contractile muscle models. This implies that a population responds to a change in environmental temperature as a function al system.
• 3.3.|The analysis of individual differences in the pattern of response of muscles, and their contractile models, to changes in environmental temperature allows the systemal and individual components to be isolated. The extent of co-ordination in responses of different individuals of the population can be evaluated from the proportion of the systemal component. The value of this component varies from 0.60 to 0.90.
• 4.4.|Selective advantage during thermal selection belongs to individuals with lower heat resistance of muscles.

     

Tritium NMR studies of the human carbonic anhydrase I–benzenesulfonamide complex

Tritium NMR spectroscopy has been used to examine the complexformed by [4-³H]benzenesulfon-amide and human carbonicanhydrase I. The results show that in solution the inhibitor forms a 1:1complex with the enzyme. A 100-spin computational model of the system,constructed with reference to crystallographic results, was used tointerpret tritium relaxation behavior and ³H{¹H}NOEs. The analysis shows that the rate of dissociation of theenzyme–sulfonamide complex is 0.35 s^–1 and thatthe aromatic ring of the inhibitor undergoes rapid rotation while complexed.     

The lipid–teichoic acid complex in the cytoplasmic membrane of Streptococcus faecalis N.C.I.B. 8191

1. A lipid-teichoic acid complex was isolated from Streptococcus faecalis N.C.I.B. 8191. The covalent nature of the linkage between teichoic acid and lipid was established. 2. The complex exhibits macromolecular properties in solution, and ultracentrifugation studies show that these are due to micelle formation. 3. From chemical studies it is concluded that the teichoic acid is a poly(glycerol phosphate) in which some of the glycerol hydroxyl groups possess kojibiosyl [2-O-alpha-d-glucopyranosyl-(1-->2)-alpha-d- glucopyranosyl] substituents, together with d-alanine ester residues. 4. The lipid is 1-kojibiosyl diglyceride, already known as a membrane component of this organism, with probably a phosphatidyl substituent. The phosphatidyl kojibiosyl diglyceride is attached to the teichoic acid through a phosphodiester linkage, and the chain of the teichoic acid contains 28-35 units. 5. Although the complex represents the whole of the membrane teichoic acid in this organism, only about 12% of the membrane glycolipid is associated with teichoic acid. 6. Two phosphatidyl glycolipids, closely resembling that bearing the teichoic acid, were isolated from the lipids of the organism and were partly characterized.     

Interaction of aldolase with the troponin–tropomyosin complex of bovine muscle (Short Communication)

Ultracentrifugal studies of mixtures of aldolase and the troponin-tropomyosin complex from bovine muscle showed the existence of a labile interaction between these two myofibrillar constituents in imidazole buffers, pH6.8, I 0.02-0.10 (mol/l), and the suppression of the reaction by fructose 1,6-diphosphate. Analysis of the sedimentation-velocity patterns suggests the binding of more than 2 molecules of troponin-tropomyosin/molecule of aldolase. The results illustrate the necessity of considering additional or alternative sites to F-actin to account for the observed binding of aldolase to the thin filaments of skeletal muscle.     

Spontaneous activity of foregut and hindgut visceral muscle of the locust,locusta migratoria—I. Normal activity and the effect of KCl depolarization and glutamate

1. Locust foregut and hindgut differed in their spontaneous contractility. The foregut was constantly active with regular contractions or with a fast rhythm incorporating larger irregular contractions.2. The hindgut showed bursts of large regular contractions interrupted by periods of quiescence.3. Foregut fluid, of unknown content, inhibited rhythmic contractions but induced large foregut tonic contractures.4. High KCl salines induced contractures in both gut sections, but the tension/[K]₀ curve showed no clear mechanical threshold.5. Glutamate (10⁻⁵ M) increased contraction frequency in the hindgut and stimulated quiescent preparations. At 10⁻⁴M, glutamate usually increased foregut contraction amplitude and frequency, this action being inhibited by 10⁻⁵ M tvramine.6. Considerable differences exist in natural rhythm, contractile properties and drug responses between these two divisions of locust gut.     

Histological specificity of respiratory pigments—I. Comparisons of the coelom and muscle hemoglobins of the polychaete worm travisia pupa and the echiuroid worm arhynchite pugettensis

Ion-equalized samples of hemoglobins from the blood vessels, coelomic erythrocytes, and the body-wall muscles of the polyuchaete Travisia pupa indicate that these proteins are biochemically distinct on the basis of oxygen equilibria and denaturation. The differences in oxygen affinity suggest the following oxygen transfer system: paradopial gills, via the blood, then to the coelom, and finally to the body-wall musculature. The oxygen affinities of all three pigments are exceedingly high, as might be expected for an animal that lives in an extremely oxygen-deficient environment and is markedly sensitive to oxygen poisoning even at atmospheric oxygen partial pressures. Ion-equalized preparations of hemoglobin from the coelomic erythrocytes and the body-wall muscles of the echiuroid Arynchite pugettensis have distinct oxygen equilibria. The oxygen affinity of both pigments is much lower than those of Travisia hemoglobins. The muscle hemoglogin has a lower oxygen affinity than the coelomic pigments. Lack of informatiion on the respiratory physiology of the rare echiuroid Arhynchite and absence of data on the intracellular oxygen equilibria of the hemoglobins render the physiological interpretation of these results difficult, even though it is clear that biochemical tissue specificity of hemoglobin occurs in this worm, as well as in Travisia.     

Postnatal transformations of alveolar surfactant in the rabbit: changes in pool size,pool morphology and isoforms of the 32–38 kDa apolipoprotein

To clarify perinatal transformations of surfactant we performed lung lavage in term fetuses and in 0–24-h-old newborn rabbits. Lavage fluid was separated into three pools, namely lavage pellet, lavage supernatant and cells. We found that at birth the pellet contains 94.1 ± 1.4% (S.E.) saturated phosphatidylcholine, while the supernatant and cells contain traces of it. At birth the pellet contains secreted lamellar bodies while the supernatant lacks any recognizable structure. After birth, the alveolar saturated phosphatidylcholine level increases 5.1-times in 24 h, the proportions between pools reaching adult values in 90 min (pellet = 75.9 + 4.8%, supernatant = 22.7 ± 4.9%), and small vesicles appear in the supernatant, probably originating from the turnover of alveolar surfactant during breathing. The saturated phosphatidylcholine associated with cells remains unchanged. At birth, the 32–38 kDa surfactant apolipoprotein appears to be less extensively sialylated than in adult life.     

Computer modeling and nanosecond simulation of the enzyme–substrate complex of the common lymphoblastic leukemia antigen (neprilysin) indicates shared residues at the primary specificity pocket (S1') with matrix metalloproteases

The common acute lymphoblastic leukemia antigen (neprilysin, CD10, neutral endopeptidase 24.11) is a member of the neprilysin family, and projects functions in signaling pathways in pathophysiological processes such as cancer, Alzheimer's disease and hypertension. Given its pathophysiological importance, an investigation of the natural substrate specificity of this metalloprotease is presented here through the application of enzyme-substrate modeling and molecular dynamics simulations. The results show that the substrate modeled, LATAC downward arrow FG, satisfies a complementary backbone H-bonding with Ala543-Tyr545, thereby suggested to be the putative substrate-binding beta-sheet, analogously to matrix metalloproteases. The modeling further suggests that phenylalanine at the P1' position (substrate) is directed in the same fashion as the synthetic inhibitor of the reference crystal structure and that this enzyme does not bind the P3'/P4' positions of a substrate, as other metalloproteases do. After a specific comparison with one member of the matrix metalloproteases, MMP-3, a common conserved valine residue at the primary S1' subsite was found to be shared between these two otherwise different proteases. These results may prove useful for selective drug design for neprilysin, and lay a foundation for future subsite analysis for other members of the neprilysin family.     

The immuno-enzymology of muscle proteins. I. General features of myosin and 5′-adenylic acid deaminase

Antisera produced in rabbits against electrophoretically homogeneous chicken skeletal muscle myosin A showed relative homogeneity by immunochemical criteria in only two animals. Sera from eleven other similarly injected animals showed varying degrees of heterogeneity in quantitative precipitin tests and Ouchterlony tests. Some of the antibodies in these latter antisera were directed against the small amounts of 5′-adenylic acid deaminase (AMP-deaminase) normally present in the myosin preparations.Myosin adenosinetriphosphatase (ATPase) activity is not inhibited on combination and precipitation by its specific antibody. Its K_m remains unchanged.AMP-deaminase, on the other hand, is completely inhibited.AMP-deaminase can be separated from myosin preparations by means of the antibody prepared against partially purified AMP-deaminase.The antibodies directed against myosin and those directed against AMP-deaminase are species and organ specific. This specificity is at variance with the results obtained with fluorescein-labeled antimyosin. The differences are discussed.