Galactic neutron stars I. Space and velocity distributions in the disk and in the halo

Aims. Neutron stars (NSs) produced in the Milky Way are supposedly ten to the eighth - ten to the ninth, of which only $\sim 2 \times 10^{3}$ are observed. Constraining the phase space distribution of NSs may help to characterize the yet undetected population of stellar remnants. Methods. We perform Monte Carlo simulations of NS orbits, under different assumptions concerning the Galactic potential and the distribution of progenitors and birth velocities. We study the resulting phase space distributions, focusing on the statistical properties of the NS populations in the disk and in the solar neighbourhood. Results. It is shown that $\sim 80$ percent of NSs are in bound orbits. The fraction of NSs located in a disk of radius 20 kpc and width 0.4 kpc is $\lesssim 20$ percent. Therefore the majority of NSs populate the halo. Fits for the surface density of the disk, the distribution of heights on the Galactic plane and the velocity distribution of the disk, are given. We also provide sky maps of the projected number density in heliocentric Galactic coordinates (l, b). Our results are compared with previous ones reported in the literature. Conclusions. Obvious applications of our modelling are in the revisiting of accretion luminosities of old isolated NSs, the issue of the observability of the nearest NS and the NS optical depth for microlensing events. These will be the scope of further studies.Comment: 11 pages, 15 figures, accepted for publication in Astronomy and Astrophysic

Discrete Model of Ideological Struggle Accounting for Migration

A discrete in time model of ideological competition is formulated taking into account population migration. The model is based on interactions between global populations of non-believers and followers of different ideologies. The complex dynamics of the attracting manifolds is investigated. Conversion from one ideology to another by means of (i) mass media influence and (ii) interpersonal relations is considered. Moreover a different birth rate is assumed for different ideologies, the rate being assumed to be positive for the reference population, made of initially non-believers. Ideological competition can happen in one or several regions in space. In the latter case, migration of non-believers and adepts is allowed; this leads to an enrichment of the ideological dynamics. Finally, the current ideological situation in the Arab countries and China is commented upon from the point of view of the presently developed mathematical model. The massive forced conversion by Ottoman Turks in the Balkans is briefly discussed.Comment: 24 pages, with 5 figures and 52 refs.; prepared for a Special issue of Advances in Complex System

Leptin augments coronary vasoconstriction and smooth muscle proliferation via a Rho kinase dependent pathway

Leptin has been implicated as a key upstream mediator of pathways associated with coronary vascular dysfunction and disease. The purpose of this investigation was to test the hypothesis that leptin modifies the coronary artery proteome and promotes increases in coronary smooth muscle contraction and proliferation via influences on Rho kinase signaling. Global proteomic assessment of coronary arteries from lean swine cultured with obese concentrations of leptin (30 ng/mL) for 3 days revealed significant alterations in the coronary artery proteome (68 proteins) and identified an association between leptin treatment and calcium signaling/contraction (four proteins) and cellular growth and proliferation (35 proteins). Isometric tension studies demonstrated that both acute (30 min) and chronic (3 days, serum-free media) exposure to obese concentrations of leptin potentiated depolarization-induced contraction of coronary arteries. Inhibition of Rho kinase significantly reduced leptin-mediated increases in coronary artery contractions. The effects of leptin on the functional expression of Rho kinase were time-dependent, as acute treatment increased Rho kinase activity while chronic (3 day) exposure was associated with increases in Rho kinase protein abundance. Proliferation assays following chronic leptin administration (8 day, serum-containing media) demonstrated that leptin augmented coronary vascular smooth muscle proliferation and increased Rho kinase activity. Inhibition of Rho kinase significantly reduced these effects of leptin. Taken together, these findings demonstrate that leptin promotes increases in coronary vasoconstriction and smooth muscle proliferation and indicate that these phenotypic effects are associated with alterations in the coronary artery proteome and dynamic effects on the Rho kinase pathway

Old yellow enzyme confers resistance of Hansenula polymorpha towards allyl alcohol

In the methylotrophic yeast, Hansenula polymorpha, peroxisomes are formed during growth on methanol as sole carbon and energy source and contain the key enzymes for its metabolism, one of the major enzymes being alcohol oxidase (AO). Upon a shift of these cells to glucose-containing medium, peroxisomes become redundant for growth and are rapidly degraded via a highly selective process designated macropexophagy. H. polymorpha pdd mutants are disturbed in macropexophagy and hence retain high levels of peroxisomal AO activity upon induction of this process. To enable efficient isolation of PDD genes via functional complementation, we make use of the fact that AO can convert allyl alcohol into the highly toxic compound acrolein. When allyl alcohol is added to cells under conditions that induce macropexophagy, pdd mutants die, whereas complemented pdd mutants and wild-type cells survive. Besides isolating bona fide PDD genes, we occasionally obtained pdd transformants that retained high levels of AO activity although their allyl alcohol sensitive phenotype was suppressed. These invariably contained extra copies of a gene cluster encoding omologues of Saccharomyces carlsbergensis old yellow enzyme. Our data suggest that the proteins encoded by these genes detoxify acrolein by converting it into less harmful components

Regulation of myocardial oxygen delivery in response to graded reductions in hematocrit: Role of K+ channels

This study was designed to identify mechanisms responsible for coronary vasodilation in response to progressive decreases in hematocrit. Isovolemic hemodilution was produced in open-chest, anesthetized swine via concurrent removal of 500 ml of arterial blood and the addition of 500 ml of 37 °C saline or synthetic plasma expander (Hespan, 6% hetastarch in 0.9% sodium chloride). Progressive hemodilution with Hespan resulted in an increase in coronary flow from 0.39 ± 0.05 to 1.63 ± 0.16 ml/min/g (P < 0.001) as hematocrit was reduced from 32 ± 1 to 10 ± 1% (P < 0.001). Overall, coronary flow corresponded with the level of myocardial oxygen consumption, was dependent on arterial pressures ≥ ~ 60 mmHg, and occurred with little/no change in coronary venous PO2. Anemic coronary vasodilation was unaffected by the inhibition of nitric oxide synthase (l-NAME: 25 mg/kg iv; P = 0.92) or voltage-dependent K+ (K V) channels (4-aminopyridine: 0.3 mg/kg iv; P = 0.52). However, administration of the K ATP channel antagonist (glibenclamide: 3.6 mg/kg iv) resulted in an ~ 40% decrease in coronary blood flow (P < 0.001) as hematocrit was reduced to ~ 10%. These reductions in coronary blood flow corresponded with significant reductions in myocardial oxygen delivery at baseline and throughout isovolemic anemia (P < 0.001). These data indicate that vasodilator factors produced in response to isovolemic hemodilution converge on vascular smooth muscle glibenclamide-sensitive (K ATP) channels to maintain myocardial oxygen delivery and that this response is not dependent on endothelial-derived nitric oxide production or pathways that mediate dilation via K V channels

Association Rate Constants of Ras-Effector Interactions Are Evolutionarily Conserved

Evolutionary conservation of protein interaction properties has been shown to be a valuable indication for functional importance. Here we use homology interface modeling of 10 Ras-effector complexes by selecting ortholog proteins from 12 organisms representing the major eukaryotic branches, except plants. We find that with increasing divergence time the sequence similarity decreases with respect to the human protein, but the affinities and association rate constants are conserved as predicted by the protein design algorithm, FoldX. In parallel we have done computer simulations on a minimal network based on Ras-effector interactions, and our results indicate that in the absence of negative feedback, changes in kinetics that result in similar binding constants have strong consequences on network behavior. This, together with the previous results, suggests an important biological role, not only for equilibrium binding constants but also for kinetics in signaling processes involving Ras-effector interactions. Our findings are important to take into consideration in system biology approaches and simulations of biological networks

Atg21p is essential for macropexophagy and microautophagy in the yeast Hansenula polymorpha

AbstractATG genes are required for autophagy-related processes that transport proteins/organelles destined for proteolytic degradation to the vacuole. Here, we describe the identification and characterisation of the Hansenula polymorpha ATG21 gene. Its gene product Hp-Atg21p, fused to eGFP, had a dual location in the cytosol and in peri-vacuolar dots. We demonstrate that Hp-Atg21p is essential for two separate modes of peroxisome degradation, namely glucose-induced macropexophagy and nitrogen limitation-induced microautophagy. In atg21 cells subjected to macropexophagy conditions, sequestration of peroxisomes tagged for degradation is initiated but fails to complete

HOMCOS: a server to predict interacting protein pairs and interacting sites by homology modeling of complex structures

As protein–protein interactions are crucial in most biological processes, it is valuable to understand how and where protein pairs interact. We developed a web server HOMCOS (Homology Modeling of Complex Structure, http://biunit.naist.jp/homcos) to predict interacting protein pairs and interacting sites by homology modeling of complex structures. Our server is capable of three services. The first is modeling heterodimers from two query amino acid sequences posted by users. The server performs BLAST searches to identify homologous templates in the latest representative dataset of heterodimer structures generated from the PQS database. Structure validity is evaluated by the combination of sequence similarity and knowledge-based contact potential energy as previously described. The server generates a sequence-replaced model PDB file and a MODELLER script to build full atomic models of complex structures. The second service is modeling homodimers from one query sequence. The third service is identification of potentially interacting proteins for one query sequence. The server searches the dataset of heterodimer structures for a homologous template, outputs the candidate interacting sequences in the Uniprot database homologous for the interacting partner template proteins. These features are useful for wide range of researchers to predict putative interaction sites and interacting proteins