The Effect of Coumarin on Growth, Production of Dry Matter, Protein and Nucleic Acids in Roots of Maize and Wheat and the Interaction of Coumarin with Metabolic Inhibitors

Effects of coumarin on fresh weight, dry matter, protein and nucleic acid content per cell in attached roots of maize and wheat and in whole excised elongation zones of maize were determined. The inhibition in cell length exerted by coumarin did not correspond to an inhibition of the net synthetic capacity. Coumarin treatment increased the cell surface, the production of dry matter and the protein content per cell. The dry matter and the protein content per unit surface was slightly increased or unaffected. The effect of coumann on cell shape seemed to be independent of that on dry matter production and net protein synthesis. The same was found in excised elongation zones. —The net DNA-synthesis per cell was slightly increased in attached roots by coumann treatment, but this effect was probably not correlated with the morphogenetic changes. Inhibition of DNA-synthesis with hydroxyurea did not alter the coumarin induced changes in cell shape. —The net RNA-synthesis per cell was slightly decreased after coumarin treatment, but the net RNA-synthesis per cell and the morphogenetic effects exerted by coumarin were not related with each other. Inhibition of m-RNA-synthesis with actinomycin D did not prevent the effects of coumarin on cell division, cell expansion, dry matter production and net protein synthesis. The same was true for inhibitors of protein synthesis, puromycin and p-fluorophenyl-alanine. The findings are in support of the view that coumarin affects already existing structures or enzymes. —Comparisons between coumarin and the uncouplers, DNP and dicoumarol, showed that the effects of coumarin were not, solely, due to uncoupling. SH-protecting agents, BAL, DTE and glutathione, did, with few exceptions, not reduce the morphogenetic effects of coumarin.     

Exploring the open pore of the potassium channel from Streptomyces lividans

The tetrameric potassium channel from Streptomyces lividans (KcsA) embedded in planar bilayers exhibits the following electrophysiological characteristics: (i) K+ ions can cross the pore in a highly hydrated state (nH2O > or = 6), (ii) the selectivity for K+ exceeds that for Na+ ions by 11 times, and both Ca2+ and Mg2+ are permeant, (iii) the internal side is blocked by Ba2+ ions in a voltage-dependent manner, (iv) intrinsic rectification is due to gating, depending on the direction of the electric field, (v) the internal side is pH-sensitive, and (vi) the open pore has a diameter of approximately 5.8 A. In conclusion, our results show that ion conduction and selectivity of KcsA cannot easily be reconciled with the properties deduced from the rigid crystal structure [Doyle et al., Science 280 (1998) 69-77], which must be concluded to have the pore trapped in its closed state.     

Morphological Changes in the Midgut of Aedes aegypti L. (Diptera: Culicidae) Larvae Following Exposure to an Annona coriacea (Magnoliales: Annonaceae) Extract

Bioinsecticides are important in the control of disease vectors, but data regarding their physiological effects on target insects are incomplete. This study describes morphological changes that occur in the midgut of third instar Aedes aegypti L. (Diptera: Culicidae) following treatment with a methanolic extract of Annona coriacea (Magnoliales: Annonaceae). Dissected midguts were subdivided into anterior and posterior regions and analyzed by light and scanning electron microscopy. Insects exposed to the extract displayed intense, destructive cytoplasmic vacuolization in columnar and regenerative midgut cells. The apical surfaces of columnar cells exhibited cytoplasmic protrusions oriented toward the lumen, suggesting that these cells could be involved in apocrine secretory processes and/or apoptosis. We report that A. coriacea extracts induced morphological alterations in the midgut of A. aegypti midgut larvae, supporting the use of plant extracts for control of the dengue vector.     

Modeling <Emphasis Type="Italic">Neisseria meningitidis</Emphasis> metabolism: from genome to metabolic fluxes

Background  

Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. In general, most of the recent work on N. meningitidis focuses on potential antigens and their functions, immunogenicity, and pathogenicity mechanisms. Very little work has been carried out on Neisseria primary metabolism over the past 25 years.     

Multiple histone modifications in euchromatin promote heterochromatin formation by redundant mechanisms in Saccharomyces cerevisiae

Background  

Methylation of lysine 79 on histone H3 by Dot1 is required for maintenance of heterochromatin structure in yeast and humans. However, this histone modification occurs predominantly in euchromatin. Thus, Dot1 affects silencing by indirect mechanisms and does not act by the recruitment model commonly proposed for histone modifications. To better understand the role of H3K79 methylation gene silencing, we investigated the silencing function of Dot1 by genetic suppressor and enhancer analysis and examined the relationship between Dot1 and other global euchromatic histone modifiers.     

Insights into [FeFe]-hydrogenase structure, mechanism, and maturation

Hydrogenases are metalloenzymes that are key to energy metabolism in a variety of microbial communities. Divided into three classes based on their metal content, the [Fe]-, [FeFe]-, and [NiFe]-hydrogenases are evolutionarily unrelated but share similar nonprotein ligand assemblies at their active site metal centers that are not observed elsewhere in biology. These nonprotein ligands are critical in tuning enzyme reactivity, and their synthesis and incorporation into the active site clusters require a number of specific maturation enzymes. The wealth of structural information on different classes and different states of hydrogenase enzymes, biosynthetic intermediates, and maturation enzymes has contributed significantly to understanding the biochemistry of hydrogen metabolism. This review highlights the unique structural features of hydrogenases and emphasizes the recent biochemical and structural work that has created a clearer picture of the [FeFe]-hydrogenase maturation pathway.