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Jonathan E. Reyman 《American anthropologist》2000,102(3):635-636
The Land of Prehistory:. Critical History of American Archaeology. Alice Beck Kehoe. New York: Routledge, 1998. 288 pp. 相似文献
44.
A T Smith S A Sanders R N Thorneley J F Burke R R Bray 《European journal of biochemistry》1992,207(2):507-519
A horseradish peroxidase variant ([F41V] HRP-C*), in which Val replaces the conserved Phe at position 41 adjacent to the distal His, has been constructed. Its composition and spectroscopic, catalytic and substrate-binding properties were compared with those of the wild-type recombinant (HRP-C*) and plant (HRP-C) enzymes. Presteady-state kinetic measurements of the rate constant for compound I formation (k1) revealed an eightfold decrease in the reactivity of the Phe41----Val variant towards H2O2, in comparison with HRP-C or HRP-C*. Measurement of the remaining rate constants, k2 and k3, for the two single-electron reduction reactions of [F41V] HRP-C with para-aminobenzoic acid as reducing substrate, showed that they were 2.5-fold and 1.3-fold faster, respectively. In contrast, analysis of data from steady-state assays with 2,2'-azinobis(3-ethylbenzthiazoline-6-sulphonate) as reducing substrate, showed decreased reactivity of the mutant enzyme to this compound, indicating a change in substrate specificity. Over the substrate range studied, the data for HRP-C* and for [F41V] HRP-C conformed to a simple modification of the accepted peroxidase mechanism in which a first-order step (ku), assumed to be product dissociation, becomes rate-limiting under our standard assay conditions. Calculations of rate constants from steady-state data yielded values of k1 for both enzyme forms in adequate agreement with those from pre-steady state measurements. They showed, furthermore, that both k3 for 2,2'-azinobis(3-ethylbenzthiazoline-6-sulphonate) and ku were substantially decreased, fivefold and tenfold, respectively, in the mutant. Analogous to the decrease in ku, we observed a twofold increase in the affinity of the mutant variant for the inhibitor benzhydroxamic acid. The coordination-state equilibrium of the haem iron also appeared shifted towards the hexacoordinate high-spin form. These observations indicate that in addition to affecting reactivity to H2O2, mutations in the distal region and close to the haem iron also affect reactivity towards different reducing substrates, inducing perturbations in the neighbourhood of the aromatic-substrate-binding site, known to be 0.8-1.2 nm from the haem iron. 相似文献
45.
Moran Jonathan A.; Merbach Marlis A.; Livingston Nigel J.; Clarke Charles M.; Booth Webber E. 《Annals of botany》2001,88(2):307-311
Old World pitcher plants (Nepenthes spp., Nepenthaceae) trapand digest invertebrate prey to derive nutrients, primarilynitrogen (N). In the majority of lowland Nepenthes species studiedto date, ants (Hymenoptera, Formicidae) are numerically thedominant prey taxon. Nepenthes albomarginata is unusual in showingan apparent bias towards the capture of termites (Isoptera).We tested the hypothesis that N. albomarginata derives N fromtermite capture, by comparison of foliar stable N isotope abundance( 相似文献
46.
Jonathan A. Newman 《Global Change Biology》2004,10(1):5-15
Experimental evidence regarding the responses of cereal aphids to rising atmospheric CO2 has been ambiguous. Some studies suggest increased population sizes under future CO2 levels, others suggest decreased population sizes, and still others suggest little or no difference. Recently, Newman et al. (2003) constructed a general mathematical model of the aphid–grass interaction to investigate whether or not we should, in fact, expect a general aphid response to rising CO2. They concluded that aphid populations are likely to be larger under future CO2 concentrations if soil N levels are high, the aphid species' nitrogen requirement is low and the aphid species' density‐dependent response in winged morph production is weak. In that model, and in field experiments, CO2 concentration influences aphid population dynamics through the effect it has on plant quality. However, future CO2 concentrations are also likely to be accompanied by higher ambient temperatures, a combination that has received little focus to date. In the present paper, the Newman et al. model is used to consider the combined effects of increased CO2 concentrations and temperature on aphid population sizes. It is concluded that, when both factors are elevated, aphid population dynamics will be more similar to current ambient conditions than expected from the results of experiments studying either factor alone. This result has important implications for future experimentation. 相似文献
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48.
Thomas M. Becker Jack D. Poland Thomas J. Quan Mark E. White Jonathan M. Mann Allan M. Barnes 《The Western journal of medicine》1987,147(5):554-557
Meningitis caused by Yersinia pestis developed in 6 (6%) of a total of 105 patients with plague reported to the Centers for Disease Control from 1970 to 1979. Five of the six cases occurred in children aged 10 to 15 years. All six patients received antibiotic therapy before meningitis developed, which appeared between the 9th and 14th days after the onset of acute illness in five of the six patients. There were no neurologic sequelae. The antigenic and biochemical profiles of the Y pestis strains isolated from cerebrospinal fluid in the meningitis cases did not differ from those of the Y pestis strains obtained from blood and bubo aspirates in the other 99 patients, and neither did in vitro studies suggest antibiotic resistance. While plague meningitis is an uncommon complication of acute plague infection, physicians in the western United States should be aware that it may develop as much as 14 days after antibiotic therapy for the acute plague infection has been initiated. 相似文献
49.
A total of 62,811 cases of the acquired immunodeficiency syndrome (AIDS) have been reported to the World Health Organization from throughout the world. Extensive epidemiologic studies have shown that human immunodeficiency virus (HIV) infections are transmitted by three routes: sexual, parenteral and perinatal. Three geographic patterns of transmission have been defined. In pattern I, transmission occurs predominantly among homosexual and bisexual men and urban intravenous drug abusers; transmission via blood products has been controlled; the male:female sex ratio is 10:1 or more; population HIV seroprevalence is low, and perinatal transmission is uncommon (for instance, United States, western Europe). In pattern II, transmission is predominantly heterosexual and perinatal; transmission via blood products exists but is being reduced; unsterile needles and other skin-piercing instruments cause some parenteral transmission (magnitude not known); the male:female sex ratio is 1:1, and population seroprevalence often exceeds 1% (central Africa, Haiti). In pattern III, AIDS cases are just being documented and are generally due to sexual exposure abroad or imported blood products (Middle East, Asia). 相似文献
50.
Teratocarcinoma stem cells and early mouse embryos contain only a single major lamin polypeptide closely resembling lamin B 总被引:30,自引:0,他引:30
The nuclear lamina in adult mammalian somatic cells is composed of three major proteins, lamins A, B, and C. The expression of these proteins during the differentiation of teratocarcinomas and mouse embryogenesis is described. Embryos up to day 8 of gestation and embryonal carcinoma (EC) cells express only a single lamin species closely resembling, if not identical to, lamin B. Lamins A and/or C were detected in fertilized eggs, but disappear during the first 2-4 cleavage divisions, only reappearing in 8 day post-implantation embryos. These two lamins are absent from EC cells, but are strongly expressed in some of their derivatives. These results show that cells of the early mouse embryo do not have a functional requirement for lamins A and C and imply that the structural organization of the nucleus may change fundamentally during embryogenesis. 相似文献