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61.
1. In the presence of ATP, the Ca2+ pump of human red cell membranes catalyzes the hydrolysis of phosphate. The requirement for ATP of the Ca2+- activity was studied in relation to the two classes of site for ATP that are apparent during Ca2+ -ATPase activity. 2. (a) The for ATP as activator of the Ca2+ - extrapolated at 0 mM PNPP is equal to the of the Ca2+ -ATPase. (b) PNPP competes with ATP and its effectiveness is the same regardless the nucleotide acts as the substrate of the Ca2+ -ATPase or as activator of the Ca2+ -. 3. PNPP at the high-affinity site does not substitute for ATP as activator of the Ca2+ -. 4. At ATP concentrations that almost saturate the high-affinity site, Ca2+ - activity increases as a function of PNPP along an S-shaped curve, while Ca2+ -ATPase activity is partially inhibited along a curve of the same shape and apparent affinity. The fraction of Ca2+ -ATPase activity which is inhibited by PNPP is that which results from occupation of the low-affinity site by ATP. 5. Activation of the Ca2+ -ATPase by ATP at the low-affinity site is associated with inhibition of the Ca2+ - activity. Both phenomena take place with the same apparent affinity and along curves of the same shape. 6. Experimental results suggest that: (a) the Ca2+ - activity depends on ATP at the high-affinity site; (b) PNPP is hydrolyzed at the low-affinity site; (c) Ca2+ -ATPase activity at the high-affinity size persists during Ca2+ - activity. 相似文献
62.
63.
Ariel Alcides Petruk Sonia Varriale Maria Rosaria Coscia Lelio Mazzarella Antonello Merlino Umberto Oreste 《生物化学与生物物理学报:生物膜》2013
Plasma membrane lipids significantly affect assembly and activity of many signaling networks. The present work is aimed at analyzing, by molecular dynamics simulations, the structure and dynamics of the CD3 ζζ dimer in palmitoyl-oleoyl-phosphatidylcholine bilayer (POPC) and in POPC/cholesterol/sphingomyelin bilayer, which resembles the raft membrane microdomain supposed to be the site of the signal transducing machinery. Both POPC and raft-like environment produce significant alterations in structure and flexibility of the CD3 ζζ with respect to nuclear magnetic resonance (NMR) model: the dimer is more compact, its secondary structure is slightly less ordered, the arrangement of the Asp6 pair, which is important for binding to the Arg residue in the alpha chain of the T cell receptor (TCR), is stabilized by water molecules. Different interactions of charged residues with lipids at the lipid–cytoplasm boundary occur when the two environments are compared. Furthermore, in contrast to what is observed in POPC, in the raft-like environment correlated motions between transmembrane and cytoplasmic regions are observed. Altogether the data suggest that when the TCR complex resides in the raft domains, the CD3 ζζ dimer assumes a specific conformation probably necessary to the correct signal transduction. 相似文献
64.
Hayden Nunley Mikiko Nagashima Kamirah Martin Alcides Lorenzo Gonzalez Sachihiro C. Suzuki Declan A. Norton Rachel O. L. Wong Pamela A. Raymond David K. Lubensky 《PLoS computational biology》2020,16(12)
The outer epithelial layer of zebrafish retinae contains a crystalline array of cone photoreceptors, called the cone mosaic. As this mosaic grows by mitotic addition of new photoreceptors at the rim of the hemispheric retina, topological defects, called “Y-Junctions”, form to maintain approximately constant cell spacing. The generation of topological defects due to growth on a curved surface is a distinct feature of the cone mosaic not seen in other well-studied biological patterns like the R8 photoreceptor array in the Drosophila compound eye. Since defects can provide insight into cell-cell interactions responsible for pattern formation, here we characterize the arrangement of cones in individual Y-Junction cores as well as the spatial distribution of Y-junctions across entire retinae. We find that for individual Y-junctions, the distribution of cones near the core corresponds closely to structures observed in physical crystals. In addition, Y-Junctions are organized into lines, called grain boundaries, from the retinal center to the periphery. In physical crystals, regardless of the initial distribution of defects, defects can coalesce into grain boundaries via the mobility of individual particles. By imaging in live fish, we demonstrate that grain boundaries in the cone mosaic instead appear during initial mosaic formation, without requiring defect motion. Motivated by this observation, we show that a computational model of repulsive cell-cell interactions generates a mosaic with grain boundaries. In contrast to paradigmatic models of fate specification in mostly motionless cell packings, this finding emphasizes the role of cell motion, guided by cell-cell interactions during differentiation, in forming biological crystals. Such a route to the formation of regular patterns may be especially valuable in situations, like growth on a curved surface, where the resulting long-ranged, elastic, effective interactions between defects can help to group them into grain boundaries. 相似文献
65.
The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), is considered one of the main pests that affect fruit production in the world. This insect spends part of its life cycle in the soil, making it a target for entomopathogenic nematodes. This work aimed at evaluating the influence of soil temperature and moisture on the infectivity of Heterorhabditis sp. RSC01 and Steinernema carpocapsae ALL to third-instars of C. capitata, and to compare the efficiency of these isolates at five different soil temperatures (19, 22, 25, 28, and 31°C) and three levels of relative soil moisture (100, 75, and 50% of field capacity). Ten C. capitata larvae were transferred to plastic jars (12 cm × 6 cm) containing 100 g soil, followed by the application of an aqueous suspension containing 125 infective juveniles (IJ)/cm2. In the control treatment, 3 ml of distilled water was applied. Mortality evaluations were made five days later and were confirmed by observations of the characteristic symptoms and cadaver dissection. The infectivity was directly proportional to temperature increase, with maximum percent mortality of 86.7% and 80.0% for S. carpocapsae and Heterorhabditis sp., respectively, at 31°C. At 25°C, the highest mortality for both species was obtained at 75% of field capacity (96.7% and 26.7% for S. carpocapsae and Heterorhabditis sp., respectively). 相似文献
66.
Moraes IA Stussi JS Lilenbaum W Pissinatti A Luz FP Ferreira AM 《American journal of primatology》2004,64(3):337-343
The ability to reproduce in captivity is an essential component of lion tamarin (Leontopithecus) conservation programs. However, infections such as vaginitis, cervicitis, and endometritis are important diseases that may influence the reproduction of these animals. Therefore, it is important to detect continuous or occasional vaginal microbial populations, and to understand their potential role as an endogenous source of infection [Collins, 1964; Blue, 1983; Pugh et al., 1986]. Vaginal swabs were collected from 25 female tamarins of the three currently available species (L. rosalia, L. chrysopygus, and L. chrysomelas) at the Center of Primatology in Rio de Janeiro, Brazil. The swabs were processed according to standard mycological protocols, and isolates were biochemically characterized. Fungal isolates were recovered from 16 animals (64.0%). The results showed that 70.6% of the isolated microorganisms consisted of yeast, including three species of Candida (mainly C. glabrata). We suggest that this species is a resident member of the normal vaginal flora in Leontopithecus. Filamentous fungi (mainly from Trichosporon, Aspergillus, and Penicilliumgenera) constituted 29.4% of the isolates, and were considered to be transitory contaminants of the genital area. We suggest that colonization of the vaginal environment is related to the endocrine pattern associated with the reproductive status of these animals, but not to parity. 相似文献
67.
Multiple nuclear insertions of mitochondrial cytochrome b sequences in callitrichine primates 总被引:3,自引:0,他引:3
We report the presence of four nuclear paralogs of a 380-bp segment of cytochrome b in callitrichine primates (marmosets and tamarins). The mitochondrial cytochrome b sequence and each nuclear paralog were obtained from several species, allowing multiple comparisons of rates and patterns of substitution both between mitochondrial and nuclear sequences and among nuclear sequences. The mitochondrial DNA had high overall rates of molecular evolution and a strong bias toward substitutions at third codon positions. Rates of molecular evolution among the nuclear sequences were low and constant, and there were small differences in substitution patterns among the nuclear clades which were probably attributable to the small number of sites involved. A novel method of phylogenetic reconstruction based on the large difference in rates of evolution at different codon positions among mitochondrial and nuclear clades was used to determine whether different nuclear paralogs represent independent transposition events or duplications following a single insertion. This method is generally applicable in cases where differences in pattern of molecular evolution are known, and it showed that at least three of the four nuclear clades represent independent transposition events. The insertion events giving rise to two of the nuclear clades predate the divergence of the callitrichines, whereas those leading to the other two nuclear clades may have occurred in the common ancestor of marmosets. 相似文献
68.
da Silva AJ Buarque CD Brito FV Aurelian L Macedo LF Malkas LH Hickey RJ Lopes DV Noël F Murakami YL Silva NM Melo PA Caruso RR Castro NG Costa PR 《Bioorganic & medicinal chemistry》2002,10(8):2731-2738
Seven new 1,4-naphthoquinones structurally related to lapachol were synthesized from lawsone and oxygenated arylmercurials. These compounds can also be seen as pterocarpan derivatives where the A-ring was substituted by the 1,4-naphthoquinone nucleus. Pharmacological screening provided evidence of significant biological activities, including effects against proliferation of the MCF-7 human breast cancer cell line, against Herpes Simplex Virus type 2 infection, and against snake poison-induced myotoxicity. One derivative displaced flunitrazepam binding and showed benzodiazepine-like activity, suggesting novel neuroactive structural motifs. 相似文献
69.
Patricio J. Garrahan María I. Pouchan Alcides F. Rega 《The Journal of membrane biology》1970,3(1):14-25
Summary The cell membrane K+-activated phosphatase activity was measured in reconstituted ghosts of human red cells having different ionic contents and incubated in solutions of varying ionic composition. When K+-free ghosts are suspended in K+-rich media, full activation of the phosphatase is obtained. Conversely, very little ouabainsensitive activity is detected in K+-rich ghosts suspended in K+-free media. These results, together with the fact that Na+ competitively inhibits the effects of K+ only when present externally, show that the K+ site of the membrane phosphatase is located at the outer surface of the cell membrane. The Mg++ requirements for K+ activation of the membrane phosphatase are fulfilled by internal Mg++. Addition of intracellular Na+ to ATP-containing ghosts raises the apparent affinity of the enzyme for K+, suggesting that the sites where ATP and Na+ produce this effect are located at the inner surface of the cell membrane. The asymmetrical features of the membrane phosphatase are those expected from the proposed role of this enzyme in the Na+–K+-ATPase system.The authors are established investigators of the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina. 相似文献
70.
(1) Vanadate (pentavalent vanadium) inhibits with high affinity () the ATP-dependent Ca2+ efflux in reconstituted ghosts from human red cells. (2) To inhibit Ca2+ efflux vanadate has to have access to the inner surface of the cell membrane. (3) The inhibitory effect of vanadate is potentiated by intracellular Mg2+ and by intracellular K+. (4) Ca2+ in the external medium antagonizes the inhibitory effect of vanadate. 相似文献