Guanidinium chloride and urea denaturations of beta-lactoglobulin A at pH 2.0 and 25 degrees C: the equilibrium intermediate contains non-native structures (helix, tryptophan and hydrophobic patches)

We have carried out guanidinium chloride (GdmCl) and urea denaturations of bovine beta-lactoglobulin A (beta-lgA) at pH 2.0 and 25 degrees C, using far-UV and near-UV circular dichroism, near-UV absorption and tryptophan fluorescence spectroscopies. The stable intermediate state that occurs during GdmCl denaturation has been characterized by the far- and near-UV circular dichroism, tryptophan difference absorption, tryptophan fluorescence and 8-anilino-1-naphthalene sulphonic acid binding measurements. Following conclusions have been reached. (a) Urea-induced denaturation is not a two-state process. (b) GdmCl-induced denaturation is composed of two distinct two-state processes. (c) alpha-Helical content, burial of tryptophan residues and burial of hydrophobic surface area are more in the GdmCl-induced stable intermediate than those originally present in the native protein.     

Earliest South American paucituberculatans and their significance in the understanding of ‘pseudodiprotodont’ marsupial radiations

We describe the oldest Paucituberculata marsupials, from the La Barda and Las Flores localities (Argentina; Late Palaeocene, and Early–Middle Eocene), as well as from the Itaboraí Basin (Brazil; Late Palaeocene). The new taxa are represented by very scarce, although well‐preserved, dental remains. A parsimony analysis was performed in order to evaluate the phylogenetic affinities of these taxa. Representatives of both Riolestes capricornicus gen. et sp. nov. and Bardalestes hunco gen. et sp. nov. appear to be basal paucituberculatans, and their molar features give clues on the early evolution of the representatives of this order. Within the Paucituberculata we recognize two major clades: Caenolestoidea and Palaeothentoidea. We conclude that ‘pseudodiprotodont’ marsupials of the traditional literature (i.e. Polydolopimorphia + Paucituberculata) do not form a natural group. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 867–884.     

利用克雷伯肺炎杆菌限制性底物发酵生产1，3-丙二醇

研究了克雷伯肺炎杆菌（Klebsiella pneumoniae）批式流加发酵生产1,3-丙二醇的发酵工艺,根据1,3-丙二醇的生产和菌体生长相关的特点,采用营养基质限制性流加的发酵工艺,通过控制氮源氯化铵以保持细胞稳定生长。结果表明：过低的氮源浓度,细胞生长受到限制,影响产物1,3-PD的合成;过高的氮源浓度,细胞比生长速率增加,但1,3-PD关于消耗甘油的得率降低,用于生长和维持代谢所消耗的甘油量增加。以0.41 g/(L·h)的氮源流加速率,残余氯化铵浓度在0.1 g/L时,转化率和生产强度最高。发酵25 h～28 h后,1,3-丙二醇最终浓度达到52.03 g/L,生产强度为2.04 g/(L·h),相对于甘油的摩尔转化率为0.66,分别比氮源限制前提高了28.0 ％、35.1 ％及29.4 ％。通过限制性流加氯化铵,控制细胞的比生长速率,使底物甘油有效转变为发酵的目标产物1,3-PD,有效实现产物1,3-PD的高生产强度以及对甘油的高转化率。     

Demographic and genetic effects on reproduction as related to population size in a rare, perennial herb, Senecio integrifolius (Asteraceae)

Seed-set of the rare and threatened plant Senecio integrifolius increased significantly with population size. Experimental studies as well as field observations showed this to be due to density-dependent seed-set (Allee effect). Hand-pollination revealed lower seed-set, and a lower germination rate of inbred progeny than of outbred progeny, with great differences among populations. Contrary to general predictions in models of minimum viable population sizes, the present study indicates little negative effects of inbreeding in small populations. A genetic load model was invoked to explain the results, hypothesizing that purging of deleterious alleles in small populations has reduced inbreeding depression. However, no clear correlation between population size and genetic load was found. The results in this paper suggest that demographic and environmental factors are of greater immediate importance than population genetics in determining extinction probabilities of small plant populations.     

Effects of light on cyanide‐resistant respiration and alternative oxidase function in Arabidopsis seedlings

Mitochondrial alternative oxidase (AOX), the unique respiratory terminal oxidase in plants, catalyzes the energy wasteful cyanide (CN)‐resistant respiration and plays a role in optimizing photosynthesis. Although it has been demonstrated that leaf AOX is upregulated after illumination, the in vivo mechanism of AOX upregulation by light and its physiological significance are still unknown. In this report, red light and blue light‐induced AOX (especially AOX1a) expressions were characterized. Phytochromes, phototropins and cryptochromes, all these photoreceptors mediate the light‐response of AOX1a gene. When aox1a mutant seedlings were grown under a high‐light (HL) condition, photobleaching was more evident in the mutant than the wild‐type plants. More reactive oxygen species (ROS) accumulation and inefficient dissipation of chloroplast reducing‐equivalents in aox1a mutant may account for its worse adaptation to HL stress. When etiolated seedlings were exposed to illumination for 4 h, chlorophyll accumulation was largely delayed in aox1a plants. We first suggest that more reduction of the photosynthetic electron transport chain and more accumulation of reducing‐equivalents in the mutant during de‐etiolation might be the main reasons.     

Partial molar volumes of some α-amino acids in aqueous sodium acetate solutions at 308.15 K

The apparent molar volumes V_2,φ have been determined for glycine, -α-alanine, -α-amino-n-butyric acid, -valine and -leucine in aqueous solutions of 0.5, 1.0, 1.5 and 2.0 mol kg⁻¹ sodium acetate by density measurements at 308.15 K. These data have been used to derive the infinite dilution apparent molar volumes V⁰_2,φ for the amino acids in aqueous sodium acetate solutions and the standard volumes of transfer, Δ_tV⁰, of the amino acids from water to aqueous sodium acetate solutions. It has been observed that both V⁰_2,φ and Δ_tV⁰ vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. These linear correlations have been utilized to estimate the contributions of the charged end groups (NH₃⁺,COO⁻), CH₂ group and other alkyl chains of the amino acids to V⁰_2,φ and Δ_tV⁰. The results show that V⁰_2,φ values for (NH₃⁺,COO⁻) groups increase with sodium acetate concentration, and those for CH₂ are almost constant over the studied sodium acetate concentration range. The transfer volume increases and the hydration number of the amino acids decreases with increasing electrolyte concentrations. These facts indicate that strong interactions occur between the ions of sodium acetate and the charged centers of the amino acids. The volumetric interaction parameters of the amino acids with sodium acetate were calculated in water. The pair interaction parameters are found to be positive and decreased with increasing alkyl chain length of the amino acids, suggesting that sodium acetate has a stronger dehydration effect on amino acids which have longer hydrophobic alkyl chains. These phenomena are discussed by means of the cosphere overlap model.     

Accounting for cryptic population substructure enhances detection of inbreeding depression with genomic inbreeding coefficients: an example from a critically endangered marsupial

Characterizing inbreeding depression in wildlife populations can be critical to their conservation. Coefficients of individual inbreeding can be estimated from genome‐wide marker data. The degree to which sensitivity of inbreeding coefficients to population genetic substructure alters estimates of inbreeding depression in wild populations is not well understood. Using generalized linear models, we tested the power of two frequently used inbreeding coefficients that are calculated from genome‐wide SNP markers, F_H and F^^III, to predict four fitness traits estimated over two decades in an isolated population of the critically endangered Leadbeater's possum. F_H estimates inbreeding as excess observed homozygotes relative to equilibrium expectations, whereas F^^III quantifies allelic similarity between the gametes that formed an individual, and upweights rare homozygotes. We estimated F_H and F^^III from 1,575 genome‐wide SNP loci in individuals with fitness trait data (N = 179–237 per trait), and computed revised coefficients, F_H^{by group} and F^^{IIIby group}, adjusted for population genetic substructure by calculating them separately within two different genetic groups of individuals identified in the population. Using F_H or F^^III in the models, inbreeding depression was detected for survival to sexual maturity, longevity and whether individuals bred during their lifetime. F^^{IIIby group} (but not F_H^{by group}) additionally revealed significant inbreeding depression for lifetime reproductive output (total offspring assigned to each individual). Estimates of numbers of lethal equivalents indicated substantial inbreeding load, but differing between inbreeding estimators. Inbreeding depression, declining population size, and low and declining genetic diversity suggest that genetic rescue may assist in preventing extinction of this unique Leadbeater's possum population.     

Sensitive males: inbreeding depression in an endangered bird

Attempts to conserve threatened species by establishing new populations via reintroduction are controversial. Theory predicts that genetic bottlenecks result in increased mating between relatives and inbreeding depression. However, few studies of wild sourced reintroductions have carefully examined these genetic consequences. Our study assesses inbreeding and inbreeding depression in a free-living reintroduced population of an endangered New Zealand bird, the hihi (Notiomystis cincta). Using molecular sexing and marker-based inbreeding coefficients estimated from 19 autosomal microsatellite loci, we show that (i) inbreeding depresses offspring survival, (ii) male embryos are more inbred on average than female embryos, (iii) the effect of inbreeding depression is male-biased and (iv) this population has a substantial genetic load. Male susceptibility to inbreeding during embryo and nestling development may be due to size dimorphism, resulting in faster growth rates and more stressful development for male embryos and nestlings compared with females. This work highlights the effects of inbreeding at early life-history stages and the repercussions for the long-term population viability of threatened species.     

Zinc and copper of fetal organs during the second trimester of pregnancy

In fetus with a mean gestational age of 18 weeks (range 15-25, n = 14), zinc and copper concentrations in liver, femur, rib, and skeletal muscle were measured. Zinc and copper concentrations are highest in liver. A trend of decreasing liver zinc concentrations during gestational age is suggested. Zinc concentrations are significantly correlated with copper concentrations in liver and in femur, suggesting steady growth in both organs. Femur zinc values rank ca. 30% of those in liver, femur copper, ca. 2%. Zinc or copper concentrations in rib are of the same levels as in skeletal muscle. Their concentration for zinc ranks ca. 20%, for copper, ca. 5% of the values in liver. All zinc and copper values are lower than reported in third trimester fetal organs. Calculated zinc/copper molar ratios are distinctive for the various organs: in liver, 6 +/- 1, in femur, 73 +/- 8, and in soft tissues, 26 +/- 3. Calculated ratios from published values obtained from the third trimester of pregnancy show that the ratios in liver and skeletal muscle maintain these levels. The zinc/copper molar ratio can serve as an internal reference in zinc and/or copper measurements.     

Cytogenetical and biochemical characterization of a dG + dC-rich satellite DNA in the primate Cebus capucinus

A very abundant and dG + dC rich DNA satellite from primate Cebus capucinus has been characterized in its cytogenetic and biochemical properties with the purpose of studying the correlation between the staining properties of heterochromatin and the base composition of the corresponding very repetitive DNA. The staining techniques, as well as incorporation of base analogues, show that the heterochromatin segments of C. capucinus chromosomes correspond to a dG + dC-rich satellite. This satellite was detected and isolated by centrifugation in density gradient, radioactively labelled and localized by in situ hybridization on heterochromatin segments.