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Resultados filtrados por Publicador: The National Academy of Sciences

‣ The biological clock of very premature primate infants is responsive to light

Hao, Haiping; Rivkees, Scott A.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 02/03/1999 Português
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Each year more than 250,000 infants in the United States are exposed to artificial lighting in hospital nurseries with little consideration given to environmental lighting cycles. Essential in determining whether environmental lighting cycles need to be considered in hospital nurseries is identifying when the infant’s endogenous circadian clock becomes responsive to light. Using a non-human primate model of the developing human, we examined when the circadian clock, located in the hypothalamic suprachiasmatic nuclei (SCN), becomes responsive to light. Preterm infant baboons of different ages were exposed to light (5,000 lux) at night, and then changes in SCN metabolic activity and gene expression were assessed. After exposure to bright light at night, robust increases in SCN metabolic activity and gene expression were seen at ages that were equivalent to human infants at 24 weeks after conception. These data provide direct evidence that the biological clock of very premature primate infants is responsive to light.

‣ Structure of a biological oxygen sensor: A new mechanism for heme-driven signal transduction

Gong, Weimin; Hao, Bing; Mansy, Sheref S.; Gonzalez, Gonzalo; Gilles-Gonzalez, Marie A.; Chan, Michael K.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 22/12/1998 Português
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551.23344%
The FixL proteins are biological oxygen sensors that restrict the expression of specific genes to hypoxic conditions. FixL’s oxygen-detecting domain is a heme binding region that controls the activity of an attached histidine kinase. The FixL switch is regulated by binding of oxygen and other strong-field ligands. In the absence of bound ligand, the heme domain permits kinase activity. In the presence of bound ligand, this domain turns off kinase activity. Comparison of the structures of two forms of the Bradyrhizobium japonicum FixL heme domain, one in the “on” state without bound ligand and one in the “off” state with bound cyanide, reveals a mechanism of regulation by a heme that is distinct from the classical hemoglobin models. The close structural resemblance of the FixL heme domain to the photoactive yellow protein confirms the existence of a PAS structural motif but reveals the presence of an alternative regulatory gateway.

‣ Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin

Friedmann, E. Imre; Wierzchos, Jacek; Ascaso, Carmen; Winklhofer, Michael
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 27/02/2001 Português
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551.23344%
The presence of magnetite crystal chains, considered missing evidence for the biological origin of magnetite in ALH84001 [Thomas-Keprta, K. L., Bazylinski, D. A., Kirschvink, J. L., Clemett, S. J., McKay, D. S., Wentworth, S. J., Vali, H., Gibson, E. K., Jr., & Romanek, C. S. (2000) Geochim. Cosmochim. Acta 64, 4049–4081], is demonstrated by high-power stereo backscattered scanning electron microscopy. Five characteristics of such chains (uniform crystal size and shape within chains, gaps between crystals, orientation of elongated crystals along the chain axis, flexibility of chains, and a halo that is a possible remnant of a membrane around chains), observed or inferred to be present in magnetotactic bacteria but incompatible with a nonbiological origin, are shown to be present. Although it is unlikely that magnetotactic bacteria were ever alive in ALH84001, decomposed remains of such organisms could have been deposited in cracks in the rock while it was still on the surface on Mars.

‣ Site-specific mutations in the mature form of human IL-18 with enhanced biological activity and decreased neutralization by IL-18 binding protein

Kim, Soo-Hyun M.; Azam, Tania; Yoon, Do-Young; Reznikov, Leonid L.; Novick, Daniela; Rubinstein, Menachem; Dinarello, Charles A.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 13/03/2001 Português
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551.23344%
IL-18 can be considered a proinflammatory cytokine mediating disease as well as an immunostimulatory cytokine that is important for host defense against infection and cancer. The high-affinity, constitutively expressed, and circulating IL-18 binding protein (IL-18BP), which competes with cell surface receptors for IL-18 and neutralizes IL-18 activity, may act as a natural antiinflammatory as well as immunosuppressive molecule. In the present studies, the IL-18 precursor caspase-1 cleavage site was changed to a factor Xa site, and, after expression in Escherichia coli, mature IL-18 was generated by factor Xa cleavage. Mature IL-18 generated by factor Xa cleavage was fully active. Single point mutations in the mature IL-18 peptide were made, and the biological activities of the wild-type (WT) IL-18 were compared with those of the mutants. Mutants E42A and K89A exhibited 2-fold increased activity compared with WT IL-18. A double mutant, E42A plus K89A, exhibited 4-fold greater activity. Unexpectedly, IL-18BP failed to neutralize the double mutant E42A plus K89A compared with WT IL-18. The K89A mutant was intermediate in being neutralized by IL-18BP, whereas neutralization of the E42A mutant was comparable to that in the WT IL-18. The identification of E42 and K89 in the mature IL-18 peptide is consistent with previous modeling studies of IL-18 binding to IL-18BP and explains the unusually high affinity of IL-18BP for IL-18.

‣ Computational adaptive optics for live three-dimensional biological imaging

Kam, Z.; Hanser, B.; Gustafsson, M. G. L.; Agard, D. A.; Sedat, J. W.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 27/03/2001 Português
Relevância na Pesquisa
551.23344%
Light microscopy of thick biological samples, such as tissues, is often limited by aberrations caused by refractive index variations within the sample itself. This problem is particularly severe for live imaging, a field of great current excitement due to the development of inherently fluorescent proteins. We describe a method of removing such aberrations computationally by mapping the refractive index of the sample using differential interference contrast microscopy, modeling the aberrations by ray tracing through this index map, and using space-variant deconvolution to remove aberrations. This approach will open possibilities to study weakly labeled molecules in difficult-to-image live specimens.

‣ A high-speed atomic force microscope for studying biological macromolecules

Ando, Toshio; Kodera, Noriyuki; Takai, Eisuke; Maruyama, Daisuke; Saito, Kiwamu; Toda, Akitoshi
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
551.23344%
The atomic force microscope (AFM) is a powerful tool for imaging individual biological molecules attached to a substrate and placed in aqueous solution. At present, however, it is limited by the speed at which it can successively record highly resolved images. We sought to increase markedly the scan speed of the AFM, so that in the future it can be used to study the dynamic behavior of biomolecules. For this purpose, we have developed a high-speed scanner, free of resonant vibrations up to 60 kHz, small cantilevers with high resonance frequencies (450–650 kHz) and small spring constants (150–280 pN/nm), an objective-lens type of deflection detection device, and several electronic devices of wide bandwidth. Integration of these various devices has produced an AFM that can capture a 100 × 100 pixel2 image within 80 ms and therefore can generate a movie consisting of many successive images (80-ms intervals) of a sample in aqueous solution. This is demonstrated by imaging myosin V molecules moving on mica (see http://www.s.kanazawa-u.ac.jp/phys/biophys/bmv_movie.htm).

‣ Water magnetic relaxation dispersion in biological systems: The contribution of proton exchange and implications for the noninvasive detection of cartilage degradation

Duvvuri, Umamaheswar; Goldberg, Ari D.; Kranz, James K.; Hoang, Linh; Reddy, Ravinder; Wehrli, Felix W.; Wand, A. Joshua; Englander, S. W.; Leigh, John S.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
551.23344%
Magnetic relaxation has been used extensively to study and characterize biological tissues. In particular, spin-lattice relaxation in the rotating frame (T1ρ) of water in protein solutions has been demonstrated to be sensitive to macromolecular weight and composition. However, the nature of the contribution from low frequency processes to water relaxation remains unclear. We have examined this problem by studying the water T1ρ dispersion in peptide solutions (14N- and 15N-labeled), glycosaminoglycan solutions, and samples of bovine articular cartilage before and after proteoglycan degradation. We find in model systems and tissue that hydrogen exchange from NH and OH groups to water dominates the low frequency water T1ρ dispersion, in the context of the model used to interpret the relaxation data. Further, low frequency dispersion changes are correlated with loss of proteoglycan from the extra-cellular matrix of articular cartilage. This finding has significance for the noninvasive detection of matrix degradation.

‣ Degeneracy and complexity in biological systems

Edelman, Gerald M.; Gally, Joseph A.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
551.23344%
Degeneracy, the ability of elements that are structurally different to perform the same function or yield the same output, is a well known characteristic of the genetic code and immune systems. Here, we point out that degeneracy is a ubiquitous biological property and argue that it is a feature of complexity at genetic, cellular, system, and population levels. Furthermore, it is both necessary for, and an inevitable outcome of, natural selection.

‣ Release of C-type natriuretic peptide accounts for the biological activity of endothelium-derived hyperpolarizing factor

Chauhan, Sharmila D.; Nilsson, Holger; Ahluwalia, Amrita; Hobbs, Adrian J.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
551.23344%
Endothelial cells in most vascular beds release a factor that hyperpolarizes the underlying smooth muscle, produces vasodilatation, and plays a fundamental role in the regulation of local blood flow and systemic blood pressure. The identity of this endothelium-derived hyperpolarizing factor (EDHF), which is neither NO nor prostacyclin, remains obscure. Herein, we demonstrate that in mesenteric resistance arteries, release of C-type natriuretic peptide (CNP) accounts for the biological activity of EDHF. Both produce identical smooth muscle hyperpolarizations that are attenuated in the presence of high [K+], the Gi G protein (Gi) inhibitor pertussis toxin, the G protein-gated inwardly rectifying K+ channel inhibitor tertiapin, and a combination of Ba2+ (inwardly rectifying K+ channel blocker) plus ouabain (Na+/K+-ATPase inhibitor). Responses to EDHF and CNP are unaffected by the natriuretic peptide receptor (NPR)-A/B antagonist HS-142-1, but mimicked by the selective NPR-C agonist, cANF4–23. EDHF-dependent relaxation is concomitant with liberation of endothelial CNP; in the presence of the myoendothelial gap-junction inhibitor 18α-glycyrrhetinic acid or after endothelial denudation, CNP release and EDHF responses are profoundly suppressed. These data demonstrate that acetylcholine-evoked release of endothelial CNP activates NPR-C on vascular smooth muscle that via a Gi coupling promotes Ba2+/ouabain-sensitive hyperpolarization. Thus...