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221.
222.
Smith TM Olejniczak AJ Zermeno JP Tafforeau P Skinner MM Hoffmann A Radovčić J Toussaint M Kruszynski R Menter C Moggi-Cecchi J Glasmacher UA Kullmer O Schrenk F Stringer C Hublin JJ 《Journal of human evolution》2012,62(3):395-411
Recent humans and their fossil relatives are classified as having thick molar enamel, one of very few dental traits that distinguish hominins from living African apes. However, little is known about enamel thickness in the earliest members of the genus Homo, and recent studies of later Homo report considerable intra- and inter-specific variation. In order to assess taxonomic, geographic, and temporal trends in enamel thickness, we applied micro-computed tomographic imaging to 150 fossil Homo teeth spanning two million years. Early Homo postcanine teeth from Africa and Asia show highly variable average and relative enamel thickness (AET and RET) values. Three molars from South Africa exceed Homo AET and RET ranges, resembling the hyper thick Paranthropus condition. Most later Homo groups (archaic European and north African Homo, and fossil and recent Homo sapiens) possess absolutely and relatively thick enamel across the entire dentition. In contrast, Neanderthals show relatively thin enamel in their incisors, canines, premolars, and molars, although incisor AET values are similar to H. sapiens. Comparisons of recent and fossil H. sapiens reveal that dental size reduction has led to a disproportionate decrease in coronal dentine compared with enamel (although both are reduced), leading to relatively thicker enamel in recent humans. General characterizations of hominins as having ‘thick enamel’ thus oversimplify a surprisingly variable craniodental trait with limited taxonomic utility within a genus. Moreover, estimates of dental attrition rates employed in paleodemographic reconstruction may be biased when this variation is not considered. Additional research is necessary to reconstruct hominin dietary ecology since thick enamel is not a prerequisite for hard-object feeding, and it is present in most later Homo species despite advances in technology and food processing. 相似文献
223.
Human antimicrobial peptides (AMPs), including defensins, have come under intense scrutiny owing to their key multiple roles as antimicrobial agents. Not only do they display direct action on microbes, but also recently they have been shown to interact with the immune system to increase antimicrobial activity. Unfortunately, since mechanisms involved in the binding of AMPs to mammalian cells are largely unknown, their potential as novel anti-infective agents cannot be exploited yet. Following the reported interaction of Human Neutrophil Peptide 1 dimer (HNP1) with a low density lipoprotein receptor (LDLR), a computational study was conducted to discover their putative mode of interaction. State-of-the-art docking software produced a set of LDLR-HNP1 complex 3D models. Creation of a 3D motif capturing atomic interactions of the LDLR binding interface allowed selection of the most plausible configurations. Eventually, only two models were in agreement with the literature. Binding energy estimations revealed that only one of them is particularly stable, but also interaction with LDLR weakens significantly bonds within the HNP1 dimer. This may be significant since it suggests a mechanism for internalisation of HNP1 in mammalian cells. In addition to a novel approach for complex structure prediction, this study proposes a 3D model of the LDLR-HNP1 complex which highlights the key residues which are involved in the interactions. The putative identification of the receptor binding mechanism should inform the future design of synthetic HNPs to afford maximum internalisation, which could lead to novel anti-infective drugs. 相似文献
224.
Biochemical characterization of a Neisseria meningitidis polysialyltransferase reveals novel functional motifs in bacterial sialyltransferases 总被引:1,自引:1,他引:0
225.
226.
Almut G. Jones 《Brittonia》1984,36(4):463-466
Plants ofAster sandwicensis (A. Gray in H. Mann) Hieron. belong inA. subulatus Michaux but are recognized as taxonomically distinct from those of var.subulatus. A new combination is needed:A. subulatus var.sandwicensis (A. Gray in H. Mann) A. G. Jones, comb. nov.Chamisso s.n. (G-DC!) is chosen as the lectotype. 相似文献
227.
Diagnosis of bovine follicular and luteal cysts by palpation per rectum was compared with diagnosis by progesterone status, as determined by an enzymeimmunoassay (EIA). A 2x2 contingency table analysis allowed the calculation of predictive value, sensitivity and specificity for the palpation diagnosis of both cyst types. The results were 75.0, 61.9 and 50.0% for follicular cysts and 35.1, 50.0 and 61.9% for luteal cysts, respectively. The EIA results were compared to radioimmunoassay (RIA). The predictive value for a low progesterone determination (<5ng/ml) was 91.8% and for high progesterone (5ng/ml or >) it was 83.3%. The sensitivity and specificity for the EIA were both 88.2%. Within the EIA system, milk and serum samples agreed a total of 85 out of 87 times (97.7%). Definitive diagnosis of follicular or luteal cysts should not be based upon palpation per rectum alone. The EIA was found to be the better definitive diagnostic technique. 相似文献
228.
Johann S. Schwegler Wieland Steigner Almut Heuner Stefan Silbernagl 《The Journal of membrane biology》1990,117(3):243-251
Summary Confluent monolayers of the established opossum kidney cell line were exposed to NH4Cl pulses (20 mmol/liter) during continuous intracellular measurements of pH, membrane potential (PD
m
) and membrane resistance (R
m) in bicarbonate-free Ringer. The removal of extracellular NH4Cl leads to an intracellular acidification from a control value of 7.33±0.08 to 6.47±0.03 (n=7). This inhibits the absolute K conductance (g
K+), reflected by a decrease of K+ transference number from 71±3% (n=28) to 26±6% (n=5), a 2.6±0.2-fold rise ofR
m, and a depolarization by 24.2±1.5 mV (n=52). In contrast, intracellular acidification during a block ofg
K+ by 3 mmol/liter BaCl2 enhances the total membrane conductance, being shown byR
m decrease to 68±7% of control and cell membrane depolarization by 9.8±2.8 mV (n=17). Conversely, intracellular alkalinization under barium elevatesR
m and hyperpolarizes PD
m
. The replacement of extracellular sodium by choline in the presence of BaCl2 significantly hyperpolarizes PD
m
and increasesR
m, indicating the presence of a sodium conductance. This conductance is not inhibited by 10–4 mol/liter amiloride (n=7). Patch-clamp studies at the apical membrane (excised inside-out configuration) revealed two Na+-conductive channels with 18.8±1.4 pS (n=10) and 146 pS single-channel conductance. Both channels are inwardly rectifying and highly selective towards Cl–. The low-conductive channel is 4.8 times more permeable for Na+ than for K+. Its open probability rises at depolarizing potentials and is dependent on the pH of the membrane inside (higher at pH 6.5 than at pH 7.8). 相似文献
229.
Summary Needle development has been investigated in Pinus cembra at several locations in the Grisons. Special attention has been paid to longevity and senescence. Despite large variations from one tree to another, longevity (up to 12 years) appeared to increase with increasing altitude. With increasing age, contents of nutrients such as N, P, K and, to a lesser extent, Mg and S tend to decrease. Photosynthetic activity did not decline with increasing age of short shoots. Senescence begins in mid-August in needles of the oldest age classes. It is associated with the mobilization and withdrawal of large proportions of N, P, K and also Mg and S, but Ca appears to be immobile. The extent of yellowing is irregular in individual trees but needle losses on a large scale are followed by reduced losses in subsequent years. 相似文献
230.
K. Nebel E. Altmann M. Mutter R. Bardi A. M. Piazzesi M. Crisma G. M. Bonora C. Toniolo 《Biopolymers》1991,31(10):1135-1148
The molecular structures of four protected isovaline- (Iva-) containing peptides to the pentamer level have been determined by x-ray diffraction. The peptides are t-Boc-Ala-(S)-Iva-Ala-OMe (t-Boc : tert-butyloxycarbonyl; OMe : methoxy) and its (R)-Iva diastereomer, and t-Boc-[Ala-(R)-Iva]2-Ala-OH and its (S)-Iva diastereomeric methyl ester analogue. The two tripeptides are folded in an open type II β-bend conformation. The fully developed right-handed 310-helix formed by the (R)-Iva pentapeptide, which includes an unusual intramolecular (acid) O? H ?O?C(peptide) H bond, is partially unfolded (near the C-terminus) in the (S) -Iva pentapeptide. 1H-nmr and Fourier transform ir absorption studies suggest that in CDCl3 solution (a) the two tripeptides maintain a type II β-bend conformation of comparable stability and (b) both diastereomeric pentapeptide sequences adopt a fully developed 310-helix. A comparison with the preferred conformation of other extensively investigated Cα,α-disubstituted glycines is made and the implications for the use of the Iva residue in designing conformationally constrained analogues of bioactive peptides are briefly discussed. 相似文献