Protonation,alkylation, addition and redox reactions of 16, 17 and 18 valence electron [Mo(L)(NO)('S4')] complexes [L = SPh,PMe3, NO; 'S4'2– = 1,2-Bis-(2-mercaptophenylthio)ethane(2-)]

In the quest for complexes modelling functional characteristics of metal sulfur oxidoreductases, a series of molybdenum nitrosyl complexes with sulfur-dominated coordination sphere was synthesized. Treatment of the 16, 17 and 18 valence electron (VE) complexes [Mo(L)(NO)('S₄')] (1–3) [L?=?SPh (1), PMe₃ (2), NO (3), 'S₄'^2–?=?1,2-bis-(2-mercaptophenylthio) ethane(2-)] with the Brönsted acid HBF₄ resulted in formation of different types of products. 1 and 3 were reversibly protonated at one thiolate atom of the 'S₄'^2– ligand;2, however, yielded the phosphonium salt [HPMe₃]BF₄ and the dinuclear [Mo(NO)('S₄')]₂. Alkylation of 1, 2 and 3 by Me₃OBF₄ or Et₃OBF₄ uniformly resulted in high yields of [Mo(L)(NO)(R-'S₄')]BF₄ complexes [L?=?SPh: R?=?Me (5), Et (6); L?=?PMe₃: R?=?Me (7); L?=?NO: R?=?Me (8), Et (9)] in which one thiolate atom of the 'S₄'^2– ligand had become alkylated; the NMR spectra of 5, 6, 8 and 9 indicated that only one out of four theoretically possible diastereoisomers had formed. 5 and 6 were characterized also by single-crystal X-ray structure analyses. A comparison of ν(NO) bands and redox potentials (cyclic voltammetry) of parent complexes and alkylated derivatives showed that alkylation leads to a decrease in electron density at the molybdenum center and to a positive shift in redox potentials. The 16 VE complex 1 could be reduced, also chemically, to give the corresponding 17 VE anion [1]^–, and inserted elemental sulfur into the Mo-SPh bond, forming the 18 VE phenylperthio complex [Mo(η²–SSPh)(NO)('S₄')] (11) which, upon reaction with PPh₃, gave SPPh₃ and regenerated the parent complex 1. These results are discussed with regard to the sequence of proton and electron transfer steps occurring in substrate conversions catalyzed by metal sulfur oxidoreductases.     

Global vegetation models: incorporating transient changes to structure and composition

Abstract. We describe an approach for developing a Dynamic Global Vegetation Model (DGVM) that accounts for transient changes in vegetation distribution over a decadal time scale. The DGVM structure is based on a linkage between an equilibrium global vegetation model and smaller scale ecosystem dynamics modules that simulate the rate of vegetation change. Vegetation change is classified into four basic types, based largely on the projected change in above-ground biomass of the vegetation. These four types of change are: (1) dieback of forest, shrubland or grassland; (2) successional replacement within forest, shrubland or grassland; (3) invasion of forest, shrubland or grassland; (4) change in tree/grass ratio. We then propose an approach in which the appropriate ecosystem dynamics module for each type of change is applied and the grid cells of the global model updated accordingly. An approach for accounting for fire, as an example of a disturbance which may strongly influence the rate and spatial pattern of forest dieback, is incorporated. We also discuss data needs for the development, calibration and validation of the model.     

The application of robotics and mass spectrometry to the characterisation of the Drosophila melanogaster indirect flight muscle proteome

The rapid accumulation of sequence data generated by the various genome sequencingprojects and the generation of expressed sequence tag databases has resulted in the need forthe development of fast and sensitive methods for the identification and characterisation oflarge numbers of gel electrophoretically separated proteins to translate the sequence data intobiological function. To achieve this goal it has been necessary to devise new approaches toprotein analysis: matrix-assisted laser desorption and electrospray mass spectrometry havebecome important protein analytical tools which are both fast and sensitive. When combinedwith a robotic system for the in-gel digestion of electrophoretically separated proteins, itbecomes possible to rapidly identify many proteins by searching databases with MS data. Thepower of this combination of techniques is demonstrated by an analysis of the proteins presentin the myofibrillar lattice of the indirect flight muscle of Drosophila melanogaster. Theproteins were separated by SDS-PAGE and in-gel proteolysis was performed bothautomatically and manually. All 16 major proteins could quickly be identified by massspectrometry. Although most of the protein components were known to be present in theflight muscle, two new components were also identified. The combination of methodsdescribed offers a means for the rapid identification of large numbers of gel separatedproteins.     

Evidence for Multiple, Local Functions of Ciliary Neurotrophic Factor (CNTF) in Retinal Development: Expression of CNTF and Its Receptor and In Vitro Effects on Target Cells

Abstract: There is increasing, although largely indirect, evidence that neurotrophic factors not only function as target-derived survival factors for projection neurons, but also act locally to regulate developmental processes. We studied the expression of ciliary neurotrophic factor (CNTF) and the CNTF-specific ligand-binding α-subunit of the CNTF receptor complex (CNTFRα) in the rat retina, a well-defined CNS model system, and CNTF effects on cultured retinal neurons. Both CNTF and CNTFRα (mRNA and protein) are expressed during phases of retinal neurogenesis and differentiation. Retina-specific Müller glia are immunocytochemically identified as the site of CNTF production and CNTFRα-expressing, distinct neuronal cell types as potential CNTF targets. Biological effects on corresponding neurons in culture further support the conclusion that locally supplied CNTF plays a regulatory role in the development of various retinal cell types including ganglion cells and interneurons.     

Immunocytochemical colocalization of adhesive proteins with clathrin in human blood platelets: further evidence for coated vesicle-mediated transport of von Willebrand factor,fibrinogen and fibronectin

Coated membranes and vesicles play an important role in receptor-mediated endocytosis and intracellular trafficking in various cell types, and are also present in blood platelets. Platelets take up certain proteins from the blood plasma, such as von Willebrand factor and fibrinogen, and these substances are transferred to storage granules. The receptors for these plasma proteins on the platelet plasma membrane have been well characterized, but morphological evidence for their transport to the storage granules is not yet available. In an attempt to clarify this aspect, we employed postembedding immunocytochemistry on platelets embedded in the acrylic resin LR White. Clathrin as the major coat component of coated vesicles was localized in the cytoplasm, on the plasmic faces of -granules and the open canalicular system, and on the plasmic face of the plasma membrane. Colocalizations of the adhesive proteins, von Willebrand factor, fibrinogen and fibronectin, with clathrin could be observed at the same typical locations as coated vesicles were seen in Araldite-embedded material. These colocalizations have not been reported to date and furnish further evidence for a coated vesicle-mediated transport of blood plasma-derived adhesive proteins from their receptors on the outer plasma membrane to the -granules.     

Molecular cloning and functional expression of bacteriophage PK1E-encoded endoneuraminidase Endo NE

Homopolymeric α-2,8-linked sialic acid (PSA) has been found as a capsular component of sepsis- and meningitis-causing bacterial pathogens, and on eukaryotic cells as a post-translational modification of the neural cell adhesion molecule (NCAM). The polysaccharide is specifically recognized and degraded by a phage-encoded enzyme, the endo-N-acetylneuraminidase E (Endo NE). Endo NE therefore has become a valuable tool in the study of bacterial pathogenesis and eukaryotic morphogenesis. In this report we describe the molecular cloning of Endo NE and the expression of a functionally active recombinant enzyme. The cloned DNA sequence (2436 bp) encodes a polypeptide of 811 amino acids, which at the 5′ end contains a totally conserved neuraminidase motif. Expressed in Escherichia coli, the enzyme migrates as a single band of approximately 74 kDa in SDS-PAGE. A central domain of 669 amino acid residues is about 90% homologous to the recently cloned Endo NF. Both phage-induced lysis of bacteria and the catalysis of PSA degradation by the recombinant enzyme are efficiently inhibited by a polyclonal antiserum raised against the intact phage particle. The C-terminal region seems to be essential to enzymatic functions, as truncation of 32 amino acids outside the homology domain completely abolishes Endo NE activity. Our data also indicate that the 38 kDa protein, previously assumed to be a subunit of the Endo NE holoenzyme, is the product of a separate gene locus and is not necessary for in vitro depolymerase activity.     

Feather mites (Acari: Astigmata) and body condition of their avian hosts: a large correlative study

Feather mites are arthropods that live on or in the feathers of birds, and are among the commonest avian ectosymbionts. However, the nature of the ecological interaction between feather mites and birds remains unclear, some studies reporting negative effects of feather mites on their hosts and others reporting positive or no effects. Here we use a large dataset comprising 20 189 measurements taken from 83 species of birds collected during 22 yr in 151 localities from seven countries in Europe and North Africa to explore the correlation between feather mite abundance and body condition of their hosts. We predicted that, if wing‐dwelling feather mites are parasites, a negative correlation with host body condition should be found, while a mutualistic interaction should yield positive correlation. Although negative relationships between feather mite abundance and host body condition were found in a few species of birds, the sign of the correlation was positive in most bird species (69%). The overall effect size was only slightly positive (r =0.066). The effect of feather mite abundance explained <10% of variance in body condition in most species (87%). Results suggest that feather mites are not parasites of birds, but rather that they hold a commensalistic relationship where feather mites may benefit from feeding on uropygial gland secretions of their hosts and birds do not seem to obtain a great benefit from the presence of feather mites.