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111.
112.
Characterization of the bis(5''-nucleosidyl) tetraphosphate pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia. 总被引:4,自引:0,他引:4
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The P1P4-bis(5'-nucleosidyl) tetraphosphate asymmetrical-pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia has been purified over 11,000-fold to homogeneity. Anion-exchange chromatography resolves two major species with very similar properties. The enzyme is a single polypeptide of Mr 17,600 and is maximally active at pH 8.4 and 2 mM-Mg2+. It is inhibited by Ca2+ (IC50 = 0.9 mM with 2 mM-Mg2+) but not by Zn2+ ions. It preferentially hydrolyses P1P4-bis(5'-nucleosidyl) tetraphosphates, e.g. P1P4-bis(5'-adenosyl) tetraphosphate (Ap4A) (kcat. = 12.7 s-1; Km = 33 microM) and P1P4-bis(5'-guanosyl) tetraphosphate (Gp4G) (kcat. = 6.2 s-1; Km = 5 microM). With adenosine 5'-P1-tetraphospho-P4-5"'-guanosine (Ap4G) as substrate, there is a 4.5-fold preference for AMP and GTP as products and biphasic reaction kinetics are observed giving Km values of 4.7 microM and 34 microM, and corresponding rate constants of 6.5 s-1 and 11.9 s-1. The net rate constant for Ap4G hydrolysis is 7.6 s-1. The enzyme will also hydrolyse nucleotides with more than four phosphate groups, e.g. Ap5G, Ap6A and Gp5G are hydrolysed at 25%, 18% and 10% of the rate of Ap4A respectively. An NTP is always one of the products. Ap2A and Gp2G are not hydrolysed, while Ap3A and Gp3G are very poor substrates. When the enzyme is partially purified from embryos and larvae at different stages of development by sedimentation through a sucrose density gradient, its activity increases 3-fold during the first 12 h of pre-emergence development. This is followed by a slow decline during subsequent larval development. The similarity of this enzyme to other asymmetrical-pyrophosphohydrolases suggests that it did not evolve specifically to degrade the large yolk platelet store of Gp4G which is found in Artemia embryos, but that it probably serves the same general function in bis(5'-nucleosidyl) oligophosphate metabolism as in other cells. 相似文献
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Matthew R. McLennan 《Primates; journal of primatology》2014,55(2):173-178
Insects are a nutritious food source for many primates. In chimpanzees, insectivory is most prevalent among communities that manufacture tools to harvest social insects, particularly ants and termites. In contrast to other long-term study sites, chimpanzees (Pan troglodytes schweinfurthii) in Budongo Forest and Kibale National Park, Uganda, rarely eat insects and have small foraging tool kits, supporting speculation that infrequent insectivory—technically aided or otherwise—characterises chimpanzees in this part of Uganda’s Rift Valley. To expand the dataset for this region, insect foraging was investigated at Bulindi (25 km from Budongo) over 19 months during two studies in 2007–2008 and 2012–2013. Systematic faecal analysis demonstrated that insectivory is a habitual foraging activity at this site. Overall levels of insect consumption varied considerably across months but were not predicted by monthly changes in rainfall or fruit intake. Unlike their Budongo and Kibale counterparts, Bulindi chimpanzees often consume ants (principally weaver ants, Oecophylla longinoda) and use sticks to dig out stingless bee (Meliponini) ground nests. In other respects, however, insectivory at Bulindi conforms to the pattern observed elsewhere in this region: they do not manufacture ‘fishing’ or ‘dipping’ tools to harvest termites and aggressive or hard-to-access ants (e.g., army ants, Dorylus spp.), despite availability of suitable prey. The Bulindi data lend support to the supposition that chimpanzees in this part of the Rift Valley rarely exploit termites and Dorylus ants, apparently lacking the ‘cultural knowledge’ that would enable them to do so most efficiently (i.e., tool use). The study’s findings contribute to current debates about the relative influence of genetics, environment and culture in shaping regional and local variability in Pan foraging ecology. 相似文献
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Marleen TJ van Ampting Arjan J Schonewille Carolien Vink Robert Jan M Brummer van der Roelof Meer Ingeborg MJ Bovee-Oudenhoven 《BMC physiology》2009,9(1):6-9
Background
Glutathione, the main antioxidant of intestinal epithelial cells, is suggested to play an important role in gut barrier function and prevention of inflammation-related oxidative damage as induced by acute bacterial infection. Most studies on intestinal glutathione focus on oxidative stress reduction without considering functional disease outcome. Our aim was to determine whether depletion or maintenance of intestinal glutathione changes susceptibility of rats to Salmonella infection and associated inflammation. 相似文献119.
Carloto A Costas MJ Cameselle JC McLennan AG Ribeiro JM 《Biochimica et biophysica acta》2006,1760(10):1545-1551
Free ADP-ribose is a putative second messenger and also a potentially toxic compound due to its non-enzymic reactivity towards protein side chains. ADP-ribose hydrolysis is catalysed by NDP-sugar/alcohol pyrophosphatases of differing specificity, including a highly specific, low-K(m) ADP-ribose pyrophosphatase. In humans, a submicromolar-K(m) ADP-ribose pyrophosphatase has been purified from placenta, while recombinant NUDT9 has been described as a similarly specific enzyme with a nudix motif, but with a 10(2)-10(3) higher K(m). Here, a comparative study of both proteins is presented showing that they are in fact enzymically indistinguishable; crucially, they both have submicromolar K(m) for ADP-ribose. This study firmly supports the view that the ADP-ribose pyrophosphatase present in human tissues is a product of the NUDT9 gene. In addition, this study reveals previously unknown properties of both enzyme forms. They display the same, differential properties in the presence of Mg(2+) or Mn(2+) as activating cations with respect to substrate specificity, ADP-ribose saturation kinetics, and inhibition by fluoride. Treatment with H(2)O(2) alters the Mg(2+)/Mn(2+) responses and increases the K(m) values for ADP-ribose, changes that are reversed by DTT. The results are discussed in relation to the proposed roles for ADP-ribose in oxidative/nitrosative stress and for ADP-ribose pyrophosphatase as a protective enzyme whose function is to limit the intracellular accumulation of ADP-ribose. 相似文献
120.
António Carloto María Jesús Costas José Carlos Cameselle Alexander G. McLennan João Meireles Ribeiro 《Biochimica et Biophysica Acta (BBA)/General Subjects》2006
Free ADP-ribose is a putative second messenger and also a potentially toxic compound due to its non-enzymic reactivity towards protein side chains. ADP-ribose hydrolysis is catalysed by NDP-sugar/alcohol pyrophosphatases of differing specificity, including a highly specific, low-Km ADP-ribose pyrophosphatase. In humans, a submicromolar-Km ADP-ribose pyrophosphatase has been purified from placenta, while recombinant NUDT9 has been described as a similarly specific enzyme with a nudix motif, but with a 102–103 higher Km. Here, a comparative study of both proteins is presented showing that they are in fact enzymically indistinguishable; crucially, they both have submicromolar Km for ADP-ribose. This study firmly supports the view that the ADP-ribose pyrophosphatase present in human tissues is a product of the NUDT9 gene. In addition, this study reveals previously unknown properties of both enzyme forms. They display the same, differential properties in the presence of Mg2+ or Mn2+ as activating cations with respect to substrate specificity, ADP-ribose saturation kinetics, and inhibition by fluoride. Treatment with H2O2 alters the Mg2+/Mn2+ responses and increases the Km values for ADP-ribose, changes that are reversed by DTT. The results are discussed in relation to the proposed roles for ADP-ribose in oxidative/nitrosative stress and for ADP-ribose pyrophosphatase as a protective enzyme whose function is to limit the intracellular accumulation of ADP-ribose. 相似文献