Role of siderophore in iron uptake in cowpea Rhizobium GN1 (peanut isolate): Possible involvement of iron repressible outer membrane proteins

Abstract Siderophore produced by cowpea Rhizobium GN1 (Peanut isolate) was shown to be involved in iron uptake by this organism. Siderophore enhanced iron uptake in iron-starved cells. SDS-PAGE analysis of the outer membrane proteins showed two iron repressible outer membrane proteins with approximate molecular mass of 80 kDa and 76 kDa. A siderophore non-producing mutant, which was unable to grow on a medium containing synthetic iron chelators unless and until iron was added exogenously in the medium, could use siderophore of the wild-type for iron uptake indicating that the receptor for Fe-siderophore complex was intact in the mutant.     

Functional analysis of kinetochore assembly in Caenorhabditis elegans

In all eukaryotes, segregation of mitotic chromosomes requires their interaction with spindle microtubules. To dissect this interaction, we use live and fixed assays in the one-cell stage Caenorhabditis elegans embryo. We compare the consequences of depleting homologues of the centromeric histone CENP-A, the kinetochore structural component CENP-C, and the chromosomal passenger protein INCENP. Depletion of either CeCENP-A or CeCENP-C results in an identical "kinetochore null" phenotype, characterized by complete failure of mitotic chromosome segregation as well as failure to recruit other kinetochore components and to assemble a mechanically stable spindle. The similarity of their depletion phenotypes, combined with a requirement for CeCENP-A to localize CeCENP-C but not vice versa, suggest that a key step in kinetochore assembly is the recruitment of CENP-C by CENP-A-containing chromatin. Parallel analysis of CeINCENP-depleted embryos revealed mitotic chromosome segregation defects different from those observed in the absence of CeCENP-A/C. Defects are observed before and during anaphase, but the chromatin separates into two equivalently sized masses. Mechanically stable spindles assemble that show defects later in anaphase and telophase. Furthermore, kinetochore assembly and the recruitment of CeINCENP to chromosomes are independent. These results suggest distinct roles for the kinetochore and the chromosomal passengers in mitotic chromosome segregation.     

Signal transduction and biological function of placenta growth factor in primary human trophoblast

Placenta growth factor (PlGF), a member of the vascular endothelial growth factor family of angiogenic factors, is prominently expressed by trophoblast. In addition to its role as a paracrine angiogenic factor within the placenta and endometrium, presence of its receptor, Flt-1, on trophoblast suggests that PlGF also may have an autocrine role(s) in regulating trophoblast function. To elucidate its role in trophoblast, we examined the signal transduction and functional responses of primary human trophoblast to PlGF. Exogenous PlGF induced specific activation of the stress-activated protein kinase (SAPK) pathways, c-Jun-N terminal kinase (JNK) and p38 kinase, in primary term trophoblast with little to no induction of the extracellular signal regulated kinase (ERK-1 and -2) pathways. In contrast, PlGF induced significant ERK-1 and -2 activity in human umbilical vein endothelial cells but did not induce JNK or p38 activity. PlGF-induced activation of the SAPK signaling pathways protected trophoblast from growth factor withdrawal-induced apoptosis, but it did not protect trophoblast from apoptosis induced by the pro-inflammatory cytokines, interferon gamma and tumor necrosis factor alpha. These results provide the first direct evidence of a biochemical and functional role for PlGF/Flt-1 in normal trophoblast and suggest that aberrant PlGF expression during pregnancy may impact upon trophoblast function as well as vascularity within the placental bed.     

Effect of temperature on the saccharide composition obtained after alpha-amylolysis of starch

The hydrolysis of starch to low-molecular-weight products (normally characterised by their dextrose equivalent (DE), which is directly related to the number-average molecular mass) was studied at different temperatures. Amylopectin potato starch, lacking amylose, was selected because of its low tendency towards retrogradation at lower temperatures. Bacillus licheniformis alpha-amylase was added to 10% [w/w] gelatinised starch solutions. The hydrolysis experiments were done at 50, 70, and 90 degrees C. Samples were taken at defined DE values and these were analysed with respect to their saccharide composition. At the same DE the oligosaccharide composition depended on the hydrolysis temperature. This implies that at the same net number of bonds hydrolysed by the enzyme, the saccharide composition was different. The hydrolysis temperature also influenced the initial overall molecular-weight distribution. Higher temperatures led to a more homogenous molecular weight distribution. Similar effects were observed for alpha-amylases from other microbial sources such as Bacillus amyloliquefaciens and Bacillus stearothermophilus. Varying the pH (5.1, 6.2, and 7.6) at 70 degrees C did not significantly influence the saccharide composition obtained during B. licheniformis alpha-amylase hydrolysis. The underlying mechanisms for B. licheniformis alpha-amylase were studied using pure linear oligosaccharides, ranging from maltotriose to maltoheptaose as substrates. Activation energies for the hydrolysis of individual oligosaccharides were calculated from Arrhenius plots at 60, 70, 80, and 90 degrees C. Oligosaccharides with a degree of polymerisation exceeding that of the substrate could be detected. The contribution of these oligosaccharides increased as the degree of polymerisation of the substrate decreased and the temperature of hydrolysis increased. The product specificity decreased with increasing temperature of hydrolysis, which led to a more equal distribution between the possible products formed. Calculations with the subsite map as determined for the closely related alpha-amylase from B. amyloliquefaciens reconfirmed this finding of a decreased substrate specificity with increased temperature of hydrolysis. Copyright 1999 John Wiley & Sons, Inc.     

Influence of Proline on Rat Brain Activities of Alanine Aminotransferase,Aspartate Aminotransferase and Acid Phosphatase

Hyperprolinemia type II (HPII) is an autosomal recessive disorder caused by the severe deficiency of enzyme ¹-pyrroline-5-carboxylic acid dehydrogenase leading to tissue accumulation of proline. Chronic administration of Pro led to significant reduction of cytosolic ALT activity of olfactory lobes (50.57%), cerebrum (40%) and medulla oblongata (13.71%) only. Whereas mitochondrial ALT activity was reduced significantly in, all brain regions such as olfactory lobes (73.23%), cerebrum (70.26%), cerebellum (65.39%) and medulla oblongata (65.18%). The effect of chronic Pro administration on cytosolic AST activity was also determined. The cytosolic AST activity from olfactory lobes, cerebrum and medulla oblongata reduced by 75.71, 67.53 and 76.13%, respectively while cytosolic AST activity from cerebellum increased by 28.05%. The mitochondrial AST activity lowered in olfactory lobes (by 72.45%), cerebrum (by 78%), cerebellum (by 49.56%) and medulla oblongata (by 69.30%). In vitro studies also showed increase in brain tissue proline and decrease in glutamate levels. In vitro studies indicated that proline has direct inhibitory effect on these enzymes and glutamate levels in brain tissue showed positive correlation with AST and ALT activities. Acid phosphatase (ACP) activity reduced significantly in olfactory lobes (40.33%) and cerebrum (20.82%) whereas it elevated in cerebellum (97.32%) and medulla oblongata (76.33%). The histological studies showed degenerative changes in brain. Following proline treatment, the animals became sluggish and showed low responses to tail pricks and lifting by tails and showed impaired balancing. These observations indicate influence of proline on AST, ALT and ACP activities of different brain regions leading to lesser synthesis of glutamate thereby causing neurological dysfunctions.