Catálogo de publicaciones - revistas

<jats:p>Most aging individuals die from atherosclerosis, cancer, or dementia; but in the oldest old, loss of muscle strength resulting in frailty is the limiting factor for an individual's chances of living an independent life until death. Three hormonal systems show decreasing circulating hormone concentrations during normal aging: (i) estrogen (in menopause) and testosterone (in andropause), (ii) dehydroepiandrosterone and its sulphate (in adrenopause), and (iii) the growth hormone/insulin-like growth factor I axis (in somatopause). Physical changes during aging have been considered physiologic, but there is evidence that some of these changes are related to this decline in hormonal activity. Hormone replacement strategies have been developed, but many of their aspects remain controversial, and increasing blood hormone levels in aging individuals to those found during mid-adult life has not been uniformly proven to be safe and of benefit.</jats:p>

<jats:p> The nitric oxide synthase oxygenase domain (NOS <jats:sub>ox</jats:sub> ) oxidizes arginine to synthesize the cellular signal and defensive cytotoxin nitric oxide (NO). Crystal structures determined for cytokine-inducible NOS <jats:sub>ox</jats:sub> reveal an unusual fold and heme environment for stabilization of activated oxygen intermediates key for catalysis. A winged β sheet engenders a curved α-β domain resembling a baseball catcher's mitt with heme clasped in the palm. The location of exposed hydrophobic residues and the results of mutational analysis place the dimer interface adjacent to the heme-binding pocket. Juxtaposed hydrophobic O <jats:sub>2</jats:sub> - and polar <jats:sc>l</jats:sc> -arginine–binding sites occupied by imidazole and aminoguanidine, respectively, provide a template for designing dual-function inhibitors and imply substrate-assisted catalysis. </jats:p>

<jats:p>Archaeological plant remains from excavations at Qasr Ibrı̂m, Egypt, preserve volatile decay products trapped within internal networks of structural and storage macromolecules. These volatile components can be linked to specific degradative reactions occurring during the long-term burial of organic matter. Abundant alkyl pyrazines are characteristic by-products of the Maillard (or browning) reaction of proteins and carbohydrates and provide evidence for the reaction occurring in buried organic matter.</jats:p>

<jats:p> Mössbauer spectroscopy on inclusions in diamonds from São Luiz, Brazil, show that (Mg,Fe)O inclusions contain little Fe <jats:sup>3+</jats:sup> (Fe <jats:sup>3+</jats:sup> /ΣFe ≤ 7%), whereas inclusions with pyroxene composition (believed to have been originally in the perovskite structure) and tetragonal almandine-pyrope phase (TAPP) inclusions contain high relative amounts of Fe <jats:sup>3+</jats:sup> (Fe <jats:sup>3+</jats:sup> /ΣFe = 20 to 75%). These observations are consistent with high-pressure experiments on synthetic samples and support the idea that the inclusions originated in the lower mantle. Fe-Mg partitioning data for co-existing (Mg,Fe,Al)(Si,Al)O <jats:sub>3</jats:sub> – (Mg,Fe)O pairs also indicate that the phases were in equilibrium at the time of diamond formation in the lower mantle. </jats:p>

<jats:p>A stellar-occultation light curve for Triton shows asymmetry that can be understood if Triton's middle atmosphere is distorted from spherical symmetry. Although a globally oblate model can explain the data, the inferred atmospheric flattening is so large that it could be caused only by an unrealistic internal mass distribution or highly supersonic zonal winds. Cyclostrophic winds confined to a jet near Triton's northern or southern limbs (or both) could also be responsible for the details of the light curve, but such winds are required to be slightly supersonic. Hazes and clouds in the atmosphere are unlikely to have caused the asymmetry in the light curve.</jats:p>

<jats:p>Simulations with a climate model that asynchronously couples the atmosphere and the ocean showed that the increased amplitude of the seasonal cycle of insolation in the Northern Hemisphere 6000 years ago could have increased tropical Atlantic sea surface temperatures in late summer. The simulated increase in sea surface temperature and associated changes in atmospheric circulation enhanced the summer monsoon precipitation of northern Africa by more than 25 percent, compared with the middle Holocene simulation with prescribed modern sea surface temperatures, and provided better agreement with paleorecords of enhanced monsoons.</jats:p>

<jats:p> The formation of vibrationally excited heme upon photodissociation of carbonmonoxy myoglobin and its subsequent vibrational energy relaxation was monitored by picosecond anti-Stokes resonance Raman spectroscopy. The anti-Stokes intensity of the ν <jats:sub>4</jats:sub> band showed immediate generation of vibrationally excited hemes and biphasic decay of the excited populations. The best fit to double exponentials gave time constants of 1.9 ± 0.6 and 16 ± 9 picoseconds for vibrational population decay and 3.0 ± 1.0 and 25 ± 14 picoseconds for temperature relaxation of the photolyzed heme when a Boltzmann distribution was assumed. The decay of the ν <jats:sub>4</jats:sub> anti-Stokes intensity was accompanied by narrowing and frequency upshift of the Stokes counterpart. This direct monitoring of the cooling dynamics of the heme cofactor within the globin matrix allows the characterization of the vibrational energy flow through the protein moiety and to the water bath. </jats:p>

<jats:p>The maximal clique problem has been solved by means of molecular biology techniques. A pool of DNA molecules corresponding to the total ensemble of six-vertex cliques was built, followed by a series of selection processes. The algorithm is highly parallel and has satisfactory fidelity. This work represents further evidence for the ability of DNA computing to solve NP-complete search problems.</jats:p>

<jats:p>Electron microscopy methods have been used to visualize individual spherical and cylindrical supramolecular dendrimers, providing definitive confirmation of the structures suggested by previous x-ray diffraction analysis that assumed a microsegregated model. These dendrimers are self-assembled, self-organized, and aligned spontaneously and simultaneously in hexagonal columnar or cubic thermotropic liquid-crystal phases with high uniformity. Homeotropic and planar ordering of the hexagonal columnar liquid crystal was precisely controlled by a variety of surfaces. The stiffness of these cylinders was evaluated by examining their planar texture and its defects.</jats:p>

<jats:p> The fate of ventral epidermal cells differs among nematode species. Nonvulval cells fuse with the epidermis in <jats:italic>Caenorhabditis elegans</jats:italic> , whereas the homologous cells undergo apoptosis in <jats:italic>Pristionchus pacificus</jats:italic> . The homeotic gene <jats:italic>lin-39</jats:italic> is involved in the regulation of these epidermal cell fates. In <jats:italic>Caenorhabditis</jats:italic> , <jats:italic>lin-39</jats:italic> prevents cell fusion of potential vulval cells and specifies the vulva equivalence group. <jats:italic>Pristionchus</jats:italic> vulvaless mutants that displayed apoptosis of the vulval precursor cells were isolated, and point mutations in <jats:italic>lin-39</jats:italic> were identified. Thus, the evolution of these epidermal cell fates is driven by different intrinsic properties of homologous cells. </jats:p>