Annual carbon fixation in terrestrial populations of Nostoc commune (Cyanobacteria) from an Antarctic dry valley is driven by temperature regime

Nostoc commune Vaucher (a cyanobacterium) is a very conspicuous terrestrial primary producer in Victoria Land, continental Antarctica. Because polar ecosystems are considered to be especially sensitive to environmental changes, understanding the environmental constraints on net carbon (C) fixation by N. commune is necessary to determine the effects of environmental changes on the ecological functioning of ice‐free areas of the continent. A model describing net C fixation in terrestrial populations of N. commune in an Antarctic dry valley was constructed using field and laboratory measurements in which N. commune colonies were exposed to different combinations of incident irradiance (400–700 nm), temperature, and degree of desiccation. For desiccated N. commune mats with water content ≤ 30% saturation, net C fixation was highly variable between replicates and could not be modelled. However, for colonies at > 30% saturation, rates of net C fixation and dark respiration depended strongly on irradiance and temperature. Net C fixation reached a maximum rate of 21.6 μg C m^{− 2} s^{− 1} at irradiance of approximately 250 μmol m^{− 2} s^{− 1} and the optimum temperature of 20.5 °C. Agreement between predicted short‐term net C fixation and field and laboratory measurements allowed estimation of total seasonal fixation, using previously published environmental data. Annual net C fixation was estimated in the range 14.5–21.0 g C fixed m^{− 2}Nostoc mat, depending on year/season. Estimates for different seasons correlated with thermal time (accumulated hours above 0 °C during the year) rather than irradiance, in contrast to communities in local lacustrine environments, where irradiance is the main driver of primary productivity. In the terrestrial habitat, N. commune appears to compromise between an ability to capitalize on short periods of higher temperature and efficient utilization of lower irradiance at low temperature. The relationship between thermal time and net annual C fixation by N. commune is strongly linear.     

Structures of N-terminally acetylated proteins

Primary structures of 250 characterized proteins with N-terminally acetylated residues were correlated with residue distributions and other data. Excluding multiple forms derived from characterized species variants, the structures represent 105 different types of acetylated proteins. Results of comparisons extend previous suggestions based on fewer structures and define relationships further. The N-terminal residue that is acetylated is of a limited type and is frequently a small residue, with a heavy over-representation of serine and alanine. However, the occurrence of methionine at the acetylated position is also high, whereas that of glycine is less frequent than previously estimated. Lysine is over-represented in the N-terminal region, as is aspartic and glutamic acids at a few positions close to the acetylated N-terminus (especially the adjacent position). Finally, distributions of branched-chain residues in the N-terminal region of acetylated proteins are altered in relation to those of proteins in general, isoleucine is over-represented, and leucine and valine are under-represented. The results suggest that alpha-amino-acetylated proteins have special residues in N-terminally non-hydrophobic structures. Data are compatible with a protective function for acetylation but do not exclude further role(s) in processing or other special functions.     

顶空气相色谱法测定奥利司他原料药中有机残留溶剂

目的:建立奥利司他原料药中有机残留溶剂的测定方法。方法:采用顶空气相色谱法,DB-624毛细管色谱柱(30m×0.53mm×5μm),火焰离子化检测器(FID),程序升温测定奥利司他原料药中有机残留溶剂。结果:5种残留溶剂均完全分离,在考察的浓度范围内线性关系良好(r等于0.9999),回收率符合规定。结论:该方法专属性好,准确度和灵敏度高,可用于奥利司他原料药中残留溶剂的质量控制。     

The Stone Brusher, a New Sampler for Submerged Epilithic Material in Shallow Streams and Lakes

The Stone Brusher is designed to take qualitative or semi-quantitative samples of material attached to stones at 7–50 cm depth in running or stagnant waters. The epilithic material is dislodged from the stone surface with a rotating brush enclosed in a chamber and the material is drawn up directly into the sample bottle with an air-cylinder. The operator takes a sample quickly and without putting hands into the water. The sampling area is about 28 cm². The sampler is made of plastic, stainless steel and aluminium and weighs 3.1 kg. The equipment is robust and easily handled and it is constructed to meet the demand for standardized sampling for research and environmental monitoring and to improve working conditions for sampling personnel. The equipment allows sampling from bedrock and large stones that cannot be lifted from the bottom and it can be used for reliable sampling also in fast-flowing streams where the dislodged material is easily flushed away. Using Near-Infrared Spectroscopy and diatom analyses, this new sampler is evaluated in comparison to the recognized toothbrush method, which indicates that the Stone Brusher reduces sampling variability compared with the toothbrush method.     

Spectroscopic characterization of the polycrystalline copper(I) di-n-butyldithiophosphate cluster - Cu8[S2P(O-n-Bu)2]6(μ8-S): Solid-state P CP/MAS and static Cu NMR studies

A polycrystalline copper(I) O,O′-di-n-butyldithiophosphate cluster compound, Cu₈[S₂P(O-n-Bu)₂]₆(μ₈-S), was synthesized and characterized by ³¹P CP/MAS NMR at 8.46 T and static ⁶⁵Cu NMR at multiple magnetic field strengths (7.05, 9.4 and 14.1 T). The principal values of the ³¹P chemical shift tensor and the ⁶⁵Cu chemical shift and quadrupolar splitting parameters are presented. The data are compared to those for the analogous octa-nuclear cluster compounds [Cu₈(S₂P(OEt)₂)₆(μ₈-S)], [Cu₈(S₂P(O-n-Pr)₂)₆(μ₈-S)] and [Cu₈(S₂P(O-i-Bu)₂)₆(μ₈-S)]. The transverse relaxation time constant, T₂, for the [Cu₈(S₂P(O-n-Bu)₂)₆(μ₈-S)] cluster compound was found to be 160 ± 8 μs. Possible intra-molecular motions in the cluster structures in terms of size and branching of the hydrocarbon chains are discussed as reasons for the different ⁶⁵Cu NMR responses of the systems.     

Molecular model of human CYP21 based on mammalian CYP2C5: structural features correlate with clinical severity of mutations causing congenital adrenal hyperplasia

Enhanced understanding of structure-function relationships of human 21-hydroxylase, CYP21, is required to better understand the molecular causes of congenital adrenal hyperplasia. To this end, a structural model of human CYP21 was calculated based on the crystal structure of rabbit CYP2C5. All but two known allelic variants of missense type, a total of 60 disease-causing mutations and six normal variants, were analyzed using this model. A structural explanation for the corresponding phenotype was found for all but two mutants for which available clinical data are also discrepant with in vitro enzyme activity. Calculations of protein stability of modeled mutants were found to correlate inversely with the corresponding clinical severity. Putative structurally important residues were identified to be involved in heme and substrate binding, redox partner interaction, and enzyme catalysis using docking calculations and analysis of structurally determined homologous cytochrome P450s (CYPs). Functional and structural consequences of seven novel mutations, V139E, C147R, R233G, T295N, L308F, R366C, and M473I, detected in Scandinavian patients with suspected congenital adrenal hyperplasia of different severity, were predicted using molecular modeling. Structural features deduced from the models are in good correlation with clinical severity of CYP21 mutants, which shows the applicability of a modeling approach in assessment of new CYP21 mutations.     

Human C4b-binding protein, structural basis for interaction with streptococcal M protein, a major bacterial virulence factor

Human C4b-binding protein (C4BP) protects host tissue, and those pathogens able to hijack this plasma glycoprotein, from complement-mediated destruction. We now show that the first two complement control protein (CCP) modules of the C4BP alpha-chain, plus the four residues connecting them, are necessary and sufficient for binding a bacterial virulence factor, the Streptococcus pyogenes M4 (Arp4) protein. Structure determination by NMR reveals two tightly coupled CCP modules in an elongated arrangement within this region of C4BP. Chemical shift perturbation studies demonstrate that the N-terminal, hypervariable region of M4 binds to a site including strand 1 of CCP module 2. This interaction is accompanied by an intermodular reorientation within C4BP. We thus provide a detailed picture of an interaction whereby a pathogen evades complement.     

Bandpass filtering of DNA elastic modes using confinement and tension

During a variety of biological and technological processes, biopolymers are simultaneously subject to both confinement and external forces. Although significant efforts have gone into understanding the physics of polymers that are only confined, or only under tension, little work has been done to explore the effects of the interplay of force and confinement. Here, we study the combined effects of stretching and confinement on a polymer's configurational freedom. We measure the elastic response of long double-stranded DNA molecules that are partially confined to thin, nanofabricated slits. We account for the data through a model in which the DNA's short-wavelength transverse elastic modes are cut off by applied force and the DNA's bending stiffness, whereas long-wavelength modes are cut off by confinement. Thus, we show that confinement and stretching combine to permit tunable bandpass filtering of the elastic modes of long polymers.