The uptake of protons by heme-linked ionizable groups on azide binding to methemoglobin

When azide ion reacts with methemoglobin in unbuffered solution the pH of the solution increases. This phenomenon is associated with increases in the pK values of heme-linked ionizable groups on the protein which give rise to an uptake of protons from solution. We have determined as a function of pH the proton uptake, Ah', on azide binding to methemoglobin at 20°C. Data for methemoglobins A (human), guinea pig and pigeon are fitted to a theoretical expression based on the electrostatic effect of three sets of heme-linked ionizable groups on the binding of the ligand. From these fits the pK values of heme-linked ionizable groups are obtained for liganded and unliganded methemoglobins. In unliganded methemoglobin pK1, which is associated with carboxylic acid groups, ranges between 4.0 and 5.5 for the three methemoglobins; pK,, which is associated with histidines and terminal amino groups, ranges from 6.2 to 6.7. In liganded methemoglobin pK1 lies between 5.8 and 6.3 and pK, varies from 8.1 to 8.5. The pH dependences of the apparent equilibrium constants for azide binding to the three methemoglobins at 20°C are well accounted for with the pK values calculated from the variation of Ah' with pH

The Effect of Heme-linked Ionizable Groups on Cyanide Binding to Methemoglobin*

The pH dependence of the kinetics of the binding of cyanide ion to methemoglobins A and S and to guinea pig and pigeon methemoglobins appears to be not directly correlated with the net charges on the proteins. The kinetics can, howeverb, e adequately explained in terms of three sets of heme-linked ionizable groups with pK, ranging between 4.9 and 5.3, pK, between 6.2 and 7.9, and pK3 between 8.0 and 8.5 at 20 “C. pK1 is assigned to carboxylic acid groups, pKZ to histidines and terminal amino groups, and pK3 to the acidalkaline methemoglobin transition. Kinetic second order rate constants have also been determined for the binding of cyanide ion by the four sets of methemoglobin species present in solution. The pKi values and the rate constants of methemoglobin S are strikingly different from those of methemoglobin A. This result is explained in terms of different electrostatic contributions to the free energy of heme linkage arising from differences in the environments of ionizable groups at the surfaces of the two molecules

The Changing Narratives of Death, Dying, and HIV in the United Kingdom

Death and infection were closely linked from the start of the HIV epidemic, until successful treatments became available. The initial impact of mostly young, gay men dying from HIV was powerful in shaping UK responses. Neoliberal discourses developed at the same time, particularly focusing on how citizens (rather than the state) should take responsibility to improve health. Subsequently “successful ageing” became an allied discourse, further marginalising death discussions. Our study reflected on a broad range of meanings around death within the historical UK epidemic, to examine how dying narratives shape contemporary HIV experiences. Fifty-one participants including people living with HIV, professionals, and activists were recruited for semistructured interviews. Assuming a symbolic interactionist framework, analysis highlighted how HIV deaths were initially experienced as not only traumatic but also energizing, leading to creativity. With effective antiretrovirals, dying changed shape (e.g., loss of death literacy), and better integration of palliative care was recommended

Axions and White Dwarfs

White dwarfs are almost completely degenerate objects that cannot obtain energy from the thermonuclear sources and their evolution is just a gravothermal process of cooling. The simplicity of these objects, the fact that the physical inputs necessary to understand them are well identified, although not always well understood, and the impressive observational background about white dwarfs make them the most well studied Galactic population. These characteristics allow to use them as laboratories to test new ideas of physics. In this contribution we discuss the robustness of the method and its application to the axion case.Comment: 4 pages, 1 figure, to appear in the Proceedings for the 6th Patras meeting on Axions, WIMPs and WISP

Ageing with HIV

Applying Fraser’s inequalities framework to our UK-based HIV and Later Life (HALL) study, we show that, for the growing population of older people living with HIV (PLWH), HIV intersects with ethnicity, sex, sexuality, stigma, and ageism to produce bivalent identities. These shape their experience of ageing with HIV and intersect with economic factors, the social status order, and statutory policy to subject them to socioeconomic and cultural injustices only roughly captured by Fraser’s three domains of inequality. Under recognition, the stigmatization of HIV and its exacerbation by normative ageist expectations threaten social relationships. Under resources, older PLWH’s disproportionate financial disadvantage, linked to interrupted work histories, uncertain migration status, and recent changes to benefits on which PLWH are disproportionately reliant and whose new criteria disadvantage them, make access to support from others living with HIV and from HIV organizations even more essential for mental health and wellbeing. Finally, under representation, stigma and homophobia in care settings may undermine the quality of long-term care, and defunding of HIV organizations and welfare benefit changes via neo-liberal policies and austerity measures create political disenfranchisement and barriers to social participation. Thus, Fraser’s clear-cut domains imperfectly capture factors undermining underlying causes of older PLWH’s disadvantage: HIV-specific supports (resources) established to compensate for difficulties emanating from Fraser’s recognition and resources domains are increasingly threatened by agents operating within Fraser’s representation domain. Our conclusion considers other sources of older PLWH’s underrepresentation: their waning participation in activism and advocacy on their own behalf, and inadequate attention by non-HIV organizations

The initial-final mass relationship of white dwarfs in common proper motion pairs

A promising approach to decrease the uncertainties in the initial-final mass relationship, which is still poorly constrained, is to study white dwarfs for which external constraints are available, for instance, white dwarfs in common proper motion pairs (CPMPs). Important information of the white dwarf can be inferred from the study of the companion, since they were born at the same time and with the same initial chemical composition. In this contribution, we report new results obtained from spectroscopic observations of both members of several CPMPs composed of a F, G or K type star and a DA white dwarf

Effect of manganese doping on the size effect of lead zirconate titanate thin films and the extrinsic nature of dead layers

We have investigated the size effect in lead zirconate titanate (PZT) thin films with a range of manganese (Mn) doping concentrations. We found that the size effect in the conventional Pt/PZT/Pt thin-film capacitors could be systematically reduced and almost completely eliminated by increasing Mn doping concentration. The interfacial layer at the electrode-film interface appears to disappear almost entirely for the PZT films with 2% Mn doping levels, confirmed by the fits using the conventional in-series capacitor model. Our work indicates that the size effect in ferroelectrics is extrinsic in nature, supporting the work by Saad et al. Other implications of our results have also been discussed. By comparing a variety of experimental studies in the literature we propose a scenario that the dead layer between PZT (or barium strontium titanate, BST) and metal electrodes such as Pt and Au might have a defective pyrochlore/fluorite structure (possibly with a small portion of ferroelectric perovskite phase).Comment: 21 pages, 6 figure

Topology of the polarization field in ferroelectric nanowires from first principles

The behaviour of the cross-sectional polarization field is explored for thin nanowires of barium titanate from first-principles calculations. Topological defects of different winding numbers have been obtained, beyond the known textures in ferroelectric nanostructures. They result from the inward accommodation of the polarization patterns imposed at the surface of the wire by surface and edge effects. Close to a topological defect the polarization field orients out of the basal plane in some cases, maintaining a close to constant magnitude, whereas it virtually vanishes in other cases.Comment: 4 pages, 3 figure