Chick brain glutamine synthetase and Mn2+−Mg2+ interactions

Glutamine synthetase (GS) from the chick brain was purified to apparent homogeneity by ammonium sulfate fractionation followed by affinity chromatography, electrofocusing and Sephadex G-150 chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate analysis in polyacrylamide gel. By sedimentation equilibrium analysis and gel electrophoresis analysis, it was shown that the enzyme has a subunit molecular weight of 45,000 and a native molecular weight of 364,000, which is consistent with an octameric structure. Sedimentation analysis in the presence of Mg²⁺ revealed three different forms of macromolecules corresponding respectively to a monomer, a tetramer and an octamer. Among eight cations tested (Ca²⁺, Co²⁺, Fe²⁺, Li⁺, Mg²⁺, Mn²⁺, Ni²⁺, Zn²⁺) only Co²⁺, Mg²⁺ and Mn²⁺ supported GS activity; the order of activatory ability was Mg²⁺>Co²⁺>Mn²⁺. The maximum activating effect of Mn²⁺ occurs only within a very narrow range of concentration: with an excess of cation causing strong inhibition of GS activity. For each cation, maximal GS activity occurs at a defined cation/ATP ratio. A regulatory system in which Mn²⁺, modulates the Mg²⁺ dependent GS activity, is proposed; such cation interactions may be of significance in the intracellular control of glutamine synthesis.     

Effects of Ca(II) ions on Mn(II) dynamics in chick glia and rat astrocytes: Potential regulation of glutamine synthetase

Previous studies have demonstrated that in glia and astrocytes Mn(II) is distributed with ca. 30–40% in the cytoplasm, 60–70% in mitochondria. Ca(II) ions were observed to alter both the flux rates and distribution of Mn(II) ions in primary cultues of chick glia and rat astrocytes. External (influxing) Ca(II) ions had the greatest effect on Mn(II) uptake and efflux, compared to internal (effluxing) or internal-external equilibrated Ca(II) ions. External (influxing) Ca(II) ions inhibited the net rate and extent of Mn(II) uptake but enhanced Mn(II) efflux from mitochondria. These observations differ from Ca(II)–Mn(II) effects previously reported with brain (neuronal) mitochondria. Overall, increased cytoplasmic Ca(II) acts to block Mn(II) uptake and enhance Mn(II) release by mitochondria, which serve to increase the cytoplasmic concentration of free Mn(II). A hypothesis is presented involving external L-glutamate acting through membrane receptors to mobilize cell Ca(II), which in turn causes mitochondrial Mn(II) to be released. Because the concentration of free cytoplasmic Mn(II) is poised near the K_d for Mn(II) with glutamine synthetase, a slight increase in cytoplasmic Mn(II) will directly enhance the activity of glutamine synthetase, which catalyzes removal of neurotoxic glutamate and ammonia.     

Superoxide dismutase activity in nerve cell culture

Superoxide dismutase (EC 1.15.1.1) activity was assayed in preparations obtained from several clonal lines of nerve cell culture, by enzymatic and nonenzymatic assays. The enzyme was found in dialyzed homogenates of washed cells and in partially purified fractions. The enzyme was also found in cells which had been grown in media containing 5-bromodeoxyuridine, where cell differentiation was observed.     

Study of some enzyme activities in cultured chick embryo brain nerve cells treated by chick embryo brain extracts

Brain extracts from 8-day-old chick embryos have been shown to influence morphological development of dissociated brain cells from 7-day-old chick embryos in culture. Stimulatory, effects on size of the neuronal somas and on growth of long processes were observed by adding the cytosol of the brain extract or the dialysate of the cytosol. These morphological changes parallel modifications of various enzyme activities according to the age of the cultures. Adenyl cyclase, (Na⁺, K⁺)- and Mg²⁺-ATPase, 5-nucleotidase, choline acetyltransferase, and acetylcholinesterase activities were studied between 5 and 14 days of culture. Adenyl cyclase activity was strongly stimulated at 8 days by both extracts. (Na⁺, K⁺)-and Mg²⁺-ATPase activities were stimulated in 8-day-old cultures only by the dialysate. 5-Nucleotidase activity was stimulated in 8-day-old cultures by the dialysate and in 11-day-old cultures by both extracts. Choline acetyltransferase activity was stimulated by the cytosol in 8-day-old cultures and by the dialysate in 11-day-old cultures. The total acetylcholinesterase activity was higher in 8-, 11-, and 14-day-old cultures treated with the cytosol. When the cells were treated with the dialysate, the activity was only higher in 14-day-old cultures. We also found that following the addition of brain extracts, the specific activity of the enzymes we studied was enhanced and became close to the values found in vivo during embryogenesis. Thus in parallel to the morphological modifications observed in nerve cell cultures treated by embryo brain extracts, biochemical variations especially involved in synaptogenesis and membrane development could be measured.     

In Vivo and In Vitro Effects of Some Plant Hormones on Rat Erythrocyte Carbonic Anhydrase and Glucose-6-Phosphate Dehydrogenase Activities

The present study was undertaken to determine in vivo and in vitro effects of some plant growth regulators on rat erythrocyte carbonic anhydrase (CA) and glucose-6-phosphate dehydrogenase (G6PD) activities. Both in vivo and in vitro, spermidine and kinetin did not affect enzymatic activities of CA and G6PD, whereas putrescine decreased these activities, and abscisic acid increased them. Since plants use such growth regulators, their effects should be considered on mammals consuming them since they may possess important biological effects.     

Learning Biomarker Models for Progression Estimation of Alzheimer’s Disease

Being able to estimate a patient’s progress in the course of Alzheimer’s disease and predicting future progression based on a number of observed biomarker values is of great interest for patients, clinicians and researchers alike. In this work, an approach for disease progress estimation is presented. Based on a set of subjects that convert to a more severe disease stage during the study, models that describe typical trajectories of biomarker values in the course of disease are learned using quantile regression. A novel probabilistic method is then derived to estimate the current disease progress as well as the rate of progression of an individual by fitting acquired biomarkers to the models. A particular strength of the method is its ability to naturally handle missing data. This means, it is applicable even if individual biomarker measurements are missing for a subject without requiring a retraining of the model. The functionality of the presented method is demonstrated using synthetic and—employing cognitive scores and image-based biomarkers—real data from the ADNI study. Further, three possible applications for progress estimation are demonstrated to underline the versatility of the approach: classification, construction of a spatio-temporal disease progression atlas and prediction of future disease progression.     

Expression of receptor tyrosine phosphatases during development of the retinotectal projection of the chick

Receptor tyrosine kinases and receptor protein tyrosine phosphatases (RPTPs) appear to coordinate many aspects of neural development, including axon growth and guidance. Here, we focus on the possible roles of RPTPs in the developing avian retinotectal system. Using both in situ hybridization analysis and immunohistochemistry, we show for the first time that five RPTP genes--CRYPalpha, CRYP-2, PTPmu, PTPgamma, and PTPalpha--have different but overlapping expression patterns throughout the retina and the tectum. PTPalpha is restricted to Muller glia cells and radial glia of the tectum, indicating a possible function in controlling neuronal migration. PTPgamma expression is restricted to amacrine neurons. CRYPalpha and CRYP-2 mRNAs in contrast are expressed throughout the retinal ganglion cell layer from where axons grow out to their tectal targets. PTPmu is expressed in a subset of these ganglion cells. CRYPalpha, CRYP-2, and PTPmu proteins are also localized in growth cones of retinal ganglion cell axons and are present in defined laminae of the tectum. Thus, the spatial and temporal expression of three distinct RPTP subtypes--CRYPalpha, CRYP-2, and PTPmu--are consistent with the possibility of their involvement in axon growth and guidance of the retinotectal projection.     

A modified ex vivo human whole blood model of infection for studying the pathogenesis of Neisseria meningitidis during septicemia

For the purpose of establishing a model to study host-bacteria interaction and virulence mechanisms of Neisseria meningitidis during the septic phase of disease a modified human whole blood model of infection is proposed. Compared to published whole blood models the current model was modified with respect to the initial number of viable bacteria (10(4) cfu ml(-1)), the anticoagulant used and the incubation time. The results obtained after incubation of a number of human blood samples from healthy volunteers for 24 h with serogroup B meningococci were in good agreement with findings reported from patients who suffered severe meningococcal disease.     

Genetische Ursachen der prämaturen Ovarialinsuffizienz und Ovardysgenesie

Premature ovarian insufficiency (POI) is characterized by the onset of amenorrhea before 40 years of age combined with hypergonadotropic hypogonadism. The prevalence in women aged 40 is 1%. Ovarian dysgenesis is characterized by full depletion of follicles at birth and can be seen as the most severe manifestation of POI. In most cases POI occurs as an isolated condition but can also be part of a syndrome. Besides non-genetic factors POI can also be caused by chromosome aberrations, monogenetic defects and polygenic multifactorial inheritance. Although more than 30 genes associated with POI are known in the majority of cases the etiology of POI remains unknown.     

Androgeninsensitivität

Mutations of the androgen receptor gene cause a spectrum of androgen insensitivity phenotypes ranging from women with female external genitalia through patients with genital ambiguities to men with male genitalia but infertility. The CAG repeat in the first exon is important for transactivation of target genes of the androgen receptor and is thought to modulate androgen-dependent processes. Expansion of this repeat is the cause of X-linked spinobulbar muscular atrophy.