The role of the conserved Lys68*:Glu265 intersubunit salt bridge in aspartate aminotransferase kinetics: multiple forced covariant amino acid substitutions in natural variants

The role of the Lys68*:Glu265 intersubunit salt bridge that is conserved (Csb) in all known aspartate aminotransferases (AATases), except those of animal cytosolic, Ac (His68*:Glu265), and plant mitochondrial, Pm (Met68*:Gln265), origins, was evaluated in the Escherichia coli AATase. Two double-mutant cycles, to K68M/E265Q and the charge reversed K68E/E265K, were characterized with the context dependence (C) and impact (I) formalism, previously defined for functional chimeric analysis. Mutations of Lys68* with Glu265 fixed are generally more deleterious than the converse mutations of Glu265 with Lys68* fixed, showing that buried negative charges have greater effects than buried positive charges in this context. Replacement of the charged Lys68*:Glu265 with the K68M/E265Q neutral pair introduces relatively small effects on the kinetic parameters. The differential sensitivity of k(cat)/K(M, L-Asp) and k(cat)/K(M, alpha-KG) to salt bridge mutagenic replacements is shown by a linear-free energy relationship, in which the logarithms of the latter second order rate constants are generally decreased by a factor of two more than are those of the former. Thus, k(cat)/K(M, L-Asp) and k(cat)/K(M, alpha-KG) are 133 and 442 mM(-1)s(-1) for the wild-type (WT) enzyme, respectively, but their relative order is reversed in the more severely compromised mutants (14.8 and 5.3 mM(-1)s(-1) for K68E). A Venn diagram illustrates apparent forced covariances of groups of amino acids that accompany the naturally occurring salt bridge replacements in the Pm and Ac classes. The more deeply rooted tree indicates that the Csb variant was the ancestral specie.     

The amylin peptide implicated in type 2 diabetes stimulates copper-mediated carbonyl group and ascorbate radical formation

Human amylin (hA), which is toxic to islet β-cells, can self-generate H₂O₂, and this process is greatly enhanced in the presence of Cu(II) ions. Here we show that carbonyl groups, a marker of oxidative modification, were formed in hA incubated in the presence of Cu(II) ions or Cu(II) ions plus H₂O₂, but not in the presence of H₂O₂ alone. Furthermore, under similar conditions (i.e., in the presence of both Cu(II) ions and H₂O₂), hA also stimulated ascorbate radical formation. The same observations concerning carbonyl group formation were made when the histidine residue (at position 18) in hA was replaced by alanine, indicating that this residue does not play a key role. In complete contrast to hA, rodent amylin, which is nontoxic, does not generate H₂O₂, and binds Cu(II) ions only weakly, showed none of these properties. We conclude that the hA-Cu(II)/Cu(I) complex is redox active, with electron donation from the peptide reducing the oxidation state of the copper ions. The complex is capable of forming H₂O₂ from O₂ and can also generate ^•OH via Fenton chemistry. These redox properties of hA can explain its ability to stimulate copper-mediated carbonyl group and ascorbate radical formation. The formation of reactive oxygen species from hA in this way could hold the key to a better understanding of the damaging consequences of amyloid formation within the pancreatic islets of patients with type 2 diabetes mellitus.     

The analysis of data in studies of invertebrate reproduction. I. Introduction and statistical analysis of gonad indices and maturity indices

As studies of invertebrate reproduction are expensive in time and money, there is a need to make the maximum use of the resultant data. It is also important to ensure that the conclusions of a study can be legitimately drawn from the data. Both of these factors necessitate the development of appropriate statistical methodology in reproductive biology.

The structure of data in reproductive biology is detailed, and methods of analysing gonad indices and maturity indices are reviewed. Although gonad indices have been widely used, they are only really satisfactory in species with strong seasonality of reproduction. There is, however, considerable scope for extracting more information from gonad indices than is usually obtained. The value of periodic regression as a tool to aid the understanding of reproductive cycles deserves further investigation.

If microscopic preparations of the gonads are being produced to estimate maturity indices, it is definitely worthwhile measuring oocyte sizes in the females, as the amount of information gained is considerable.     

Long-Term Variation in Small Mammal Abundance in Forest and Savanna of Bolivian Cerrado

Small mammals were trapped annually in two savanna and two forest plots in cerrado habitats of Noel Kempff Mercado National Park, Santa Cruz, Bolivia, for 5–10 yr. Eighteen species were captured in forest and seven species in savanna. Species numbers and total number of individuals captured were tightly correlated. In forest, species and abundance varied interannually by up to fourfold in one plot and to 100-fold in the other, and showed alternating highs and lows as is typical for small mammals. The largest faunal differences were due not to site differences, but to year differences, with markedly different patterns in forests and savannas. Abundance was not correlated with rainfall overall, but showed correlation in exceptional years of rainfall and ENSO drought. In savanna, species and overall abundance declined without recovery during 3 yr after reaching minimum numbers in 2004. One species, Cavia aperea , became extinct on both plots, and subsequently, apparently on the entire savanna. Both herbivorous and insectivorous species declined together. Rainfall, fire, and flooding do not seem to account for savanna rodent declines. I propose the novel hypothesis that smoke from anthropogenic burning raises nocturnal temperatures and prevents dew formation, and that a decrease in nightly dry season dewfall has been instrumental in rodent declines. Anecdotal and climatic data are consistent with this hypothesis, but it cannot yet be tested.     

Cuprizone demyelination of the corpus callosum in mice correlates with altered social interaction and impaired bilateral sensorimotor coordination

For studies of remyelination in demyelinating diseases, the cuprizone model of CC (corpus callosum) demyelination has experimental advantages that include overall size, proximity to neural stem cells of the subventricular zone, and correlation with a lesion predilection site in multiple sclerosis. In addition, cuprizone treatment can be ended to allow more direct analysis of remyelination than with viral or autoimmune models. However, CC demyelination lacks a useful functional correlate in rodents for longitudinal analysis throughout the course of demyelination and remyelination. In the present study, we tested two distinct behavioural measurements in mice fed 0.2% cuprizone. Running on a ‘complex'' wheel with varied rung intervals requires integration between cerebral hemispheres for rapid bilateral sensorimotor coordination. Maximum running velocity on the ‘complex'' wheel decreased during acute (6 week) and chronic (12 week) cuprizone demyelination. Running velocity on the complex wheel distinguished treated (for 6 weeks) from non-treated mice, even after a 6-week recovery period for spontaneous remyelination. A second behavioural assessment was a resident–intruder test of social interaction. The frequency of interactive behaviours increased among resident mice after acute or chronic demyelination. Differences in both sensorimotor coordination and social interaction correlated with demonstrated CC demyelination. The wheel assay is applicable for longitudinal studies. The resident–intruder assay provides a complementary assessment of a distinct modality at a specific time point. These behavioural measurements are sufficiently robust for small cohorts as a non-invasive assessment of demyelination to facilitate analysis of subsequent remyelination. These measurements may also identify CC involvement in other mouse models of central nervous system injuries and disorders.     

Proteome profile of maize (Zea Mays L.) leaf tissue at the flowering stage after long-term adjustment to rice black-streaked dwarf virus infection

Maize rough dwarf disease (MRDD) is a viral disease and causes great yield loss. To better understand the effects of MRDD on plant growth and metabolism, comparative proteomic analysis of leaves from virus-infected and normal plants was performed. In order to eliminate the interference of Ribulose-1, 5-bisphosphate carboxylase with low-abundance proteins, total proteins were pre-fractionated by 15% PEG and the proteins from supernatant and precipitated fractions were analyzed by 2-DE, subsequently. Out of approximately 1200 protein spots detected, less than 2% of the spots on the gels were overlapping between the fractions of precipitation and supernatant. We identified 91 differentially accumulated proteins that belong to multiple metabolic/biochemical pathways in plants. Further analysis of these identified proteins indicated that MRDD resulted in dramatic changes in the fundamental metabolism, including glycolysis and starch metabolism, and eventually the significant differences in morphology and development between virus-infected and normal plants. Moreover, MRDD occurrence increased the demands for G-proteins, antioxidant enzymes, lipoxygenases and UDP-glucosyltransferase BX9, which may play important roles in response of plant against virus infection. The results also suggested that MRDD is a complicated disease controlled by multigene participating in different pathways.     

Temperature sensitivity of circadian clocks is conserved across Drosophila species melanogaster,malerkotliana and ananassae

Light and temperature are the major environmental cycles that can synchronize circadian rhythms in a variety of organisms. Previously, we have shown that under light/dark cycles of various photoperiods, the Drosophila species ananassae exhibits unimodal activity pattern with a prominent morning activity peak in contrast with Drosophila melanogaster and Drosophila malerkotliana, which show bimodal activity pattern with morning and evening activity peaks. Here we report that circadian clocks controlling activity/rest rhythm of these two less-studied species D. malerkotliana and D. ananassae can be synchronized by temperature cycles and that even under temperature cycles D. ananassae exhibits only a pronounced morning (thermophase onset) activity peak. Although D. melanogaster and D. ananassae exhibit differences in the phase of activity/rest rhythm under temperature cycles, circadian clocks of both show similar sensitivity to warm temperature pulses. Circadian period of activity/rest rhythm of D. ananassae differs from the other two species at some moderate-range temperatures; however, in conditions that are more extreme, circadian clocks of D. melanogaster, D. malerkotliana and D. ananassae appear to be largely temperature compensated.     

南极冰下水生态系统微生物与生源元素循环研究进展

南极大陆冰盖下存在液态水,形成了由冰下湖、冰下河/溪、冰封湖和冰架下水体等组成的冰下水生态系统,具有低温、黑暗和寡营养等极端的环境条件特征。微生物主导了南极冰下水生态系统,其具有丰富多样的种群构成、功能形式和独特的适应机制,在生源元素生物地球化学循环过程中起了重要作用。研究南极冰下微生物群落的生态特征及其参与的生源元素地球化学循环过程,可为揭示地球生命演化和探索外星生命提供指示,具有重要的科学意义。本文综述了南极冰下水生态系统的极端环境条件、冰下微生物的多样性、冰下微生物参与的生物地球化学循环以及冰下微生物的适极机理,最后基于研究现状展望了南极冰下微生物的未来研究方向。     

地下水微生物功能群及生物地球化学循环

地下水系统是地球关键带的重要组成部分,为微生物提供了特殊的栖息环境和复杂的生存条件,进而演化出复杂的生物地球化学过程.随着多技术、多学科的交叉融合及发展,近几十年地下水微生物功能群及生物地球化学循环研究取得了引人瞩目的 重要进展.本文从地下水中的微生物群功能分区、微生物介导的地球化学元素循环、污染与修复中的生物地球化学...