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991.
Jeremias C. Zill Zhihui He Marcus Tank Bryan H. Ferlez Daniel P. Canniffe Yigal Lahav Peter Bellstedt A. Alia Igor Schapiro John H. Golbeck Donald A. Bryant Jörg Matysik 《Photosynthesis research》2018,137(2):295-305
Photochemically induced dynamic nuclear polarization (photo-CIDNP) has been observed in the homodimeric, type-1 photochemical reaction centers (RCs) of the acidobacterium, Chloracidobacterium (Cab.) thermophilum, by 15N magic-angle spinning (MAS) solid-state NMR under continuous white-light illumination. Three light-induced emissive (negative) signals are detected. In the RCs of Cab. thermophilum, three types of (bacterio)chlorophylls have previously been identified: bacteriochlorophyll a (BChl a), chlorophyll a (Chl a), and Zn-bacteriochlorophyll a′ (Zn-BChl a′) (Tsukatani et al. in J Biol Chem 287:5720–5732, 2012). Based upon experimental and quantum chemical 15N NMR data, we assign the observed signals to a Chl a cofactor. We exclude Zn-BChl because of its measured spectroscopic properties. We conclude that Chl a is the primary electron acceptor, which implies that the primary donor is most likely Zn-BChl a′. Chl a and 81-OH Chl a have been shown to be the primary electron acceptors in green sulfur bacteria and heliobacteria, respectively, and thus a Chl a molecule serves this role in all known homodimeric type-1 RCs. 相似文献
992.
993.
Andreas Janshoff Claudia Steinem Manfred Sieber A. el Bayâ Marcus Alexander Schmidt H.-J. Galla 《European biophysics journal : EBJ》1997,26(3):261-270
The binding of cholera toxin, tetanus toxin and pertussis toxin to ganglioside containing solid supported membranes has been
investigated by quartz crystal microbalance measurements. The bilayers were prepared by fusion of phospholipid-vesicles on
a hydrophobic monolayer of octanethiol chemisorbed on one gold electrode placed on the 5 MHz AT-cut quartz crystal. The ability
of the gangliosides GM1, GM3, GD1a, GD1b, GT1b and asialo-GM1 to act as suitable receptors for the different toxins was tested by measuring the changes of quartz resonance frequencies.
To obtain the binding constants of each ligand-receptor-couple Langmuir-isotherms were successfully fitted to the experimental
adsorption isotherms. Cholera toxin shows a high affinity for GM1 (Ka = 1.8 ⋅ 108M–1), a lower one for asialo-GM1 (Ka = 1.0 ⋅ 107 M–1) and no affinity for GM3. The C-fragment of tetanus toxin binds to ganglioside GD1a, GD1b and GT1b containing membranes with similar affinity (Ka∼106 M–1), while no binding was observed with GM3. Pertussis toxin binds to membranes containing the ganglioside GD1a with a binding constant of Ka = 1.6 ⋅ 106 M–1, but only if large amounts (40 mol%) of GD1a are present. The maximum frequency shift caused by the protein adsorption depends strongly on the molecular structure of
the receptor. This is clearly demonstrated by an observed maximum frequency decrease of 99 Hz for the adsorption of the C-fragment
of tetanus toxin to GD1b. In contrast to this large frequency decrease, which was unexpectedly high with respect to Sauerbrey's equation, implying
pure mass loading, a maximum shift of only 28 Hz was detected after adsorption of the C-fragment of tetanus toxin to GD1a.
Received: 14 January 1997 / Accepted: 15 April 1997 相似文献
994.
995.
LEARNING OBJECTIVES: After studying this article, the participant should be able to: 1. Understand the mechanisms by which the three most common antithrombotic agents work. 2. Be familiar with accepted dosing levels for the three agents. 3. Understand the rationale for their use and formulate an algorithmic approach to microvascular thrombosis. Microsurgical anastomoses are largely technically dependent; however, there exists a finite rate of failure, with often devastating consequences. Pharmacologic prophylaxis and intervention are used extensively in microsurgical cases, yet a unified algorithm does not exist among the various basic science and clinical studies in the literature. This results in a confusing and nonstandardized practice based on anecdotal experiences. The purpose of this article is to review the literature on this topic and synthesize a practical clinical management algorithm for pharmacologic therapy in microsurgery. 相似文献
996.
Buecher Emmanuelle; Sparks Conrad; Brierley Andrew; Boyer Helen; Gibbons Mark 《Journal of plankton research》2001,23(10):1073-1080
Novel data on the biometry, size distribution and parasitesof Aequorea aequorea and Chrysaora hysoscella are provided frominvestigations conducted during summer and winter in the northernBenguela ecosystem. The relationship between mass and diameterof C. hysoscella did not change on a seasonal basis, and thispossibly reflects the aseasonal nature of the food environment.The changes in the size structure of C. hysoscella across theshelf and with depth agree with postulated population maintenancestrategies in the region. Aequorea aequorea was not stronglyparasitized, butC. hysoscella was subject to occasional parasitismby Hyperia medusarum, especially in winter when C. hysoscellais thought to reproduce. Parasites were distributed in a typical,negative-binomial manner on their hosts, but load was independentof host size. As medusae increased in diameter so H. medusarumtended to move from other tissues to the gonads. 相似文献
997.
G.Dastgir Qureshi Philip S. Guzelian R.Marcus Vennart Herbert J. Evans 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1985,844(3):288-295
Because of the inherent difficulties of experimentation in intact animals, we used primary monolayer cultures of non-proliferating adult rat hepatocytes to study the effects of fibrinogen degradation products on fibrinogen biosynthesis. The freshly isolated hepatocytes obtained by collagenase perfusion of the liver in situ were cultured in a chemically defined serum-free medium. The rate of fibrinogen synthesis in control cultures was cells per 24 h. Additions of 20, 60 or 100 μg of homologous stage I fibrinogen degradation products had no effect on fibrinogen synthesis. In contrast, addition of the same amounts of homologous or heterologous (human) stage III fibrinogen degradation products resulted in a concentration-dependent increase in fibrinogen biosynthesis without affecting the rate of synthesis of albumin. When purified stage III fibrinogen degradation products D and E (human) were tested in 10, 30 or 50 μg/3 ml medium only fragment E showed a significant increase in fibrinogen biosynthesis (1.9-, 2.8- and 5.6-fold, respectively, over the control cultures). The presence of excess fibrinogen had no effect. These results suggest that fibrinogen fragment E may be a specific stimulator of fibrinogen biosynthesis which may play an important role in maintaining normal levels of plasma fibrinogen. 相似文献
998.
The availability of an X-ray structure for PSII including the water-oxidizing cluster, where the metal atoms and the amino acids are assigned, has opened up new possibilities to study the mechanism for dioxygen formation. In the present paper the main results of an ongoing hybrid DFT study are presented. The model used follows the structure suggested by the X-ray analysis as closely as possible. After nearly one thousand optimizations of different structures, each one with about 70 atoms, the main features of a water oxidizing mechanism start to emerge. The key intermediate is an oxyl radical state in S(3), stabilized by a weak trans effect to a bridging oxo in the cube. To reach this radical state a structural rearrangement appears necessary, in which one additional bridging oxo is formed between the dangling manganese and a manganese in the cube. The calculated energetics is reasonable but still not fully consistent with a correct mechanism. It is suggested that some part of the structure is not correct, probably the presence of the bicarbonate. 相似文献
999.
Julie A. Coetzee Marcus J. Byrne & Martin P. Hill 《Entomologia Experimentalis et Applicata》2007,125(3):237-247
Water hyacinth [Eichhornia crassipes (Mart.) Solms (Pontederiaceae)] is the most damaging aquatic weed in South Africa, where five arthropod biological control agents have been released against it. The most recent introduction of Eccritotarsus catarinensis (Carvalho) (Heteroptera: Miridae) has failed to establish permanent populations at a number of sites in South Africa where water hyacinth is a problem. Cold winter temperatures at these sites are assumed to be the reason for these establishment failures. This assumption was tested by investigating the thermal physiology of the mirid, then incorporating these data into various predictive distribution models. Degree‐day models predict 3–14 generations per year at different localities in South Africa, and five generations at a Johannesburg site where the mirid failed to overwinter. The inability to develop sufficiently rapidly during winter months may hinder overwintering of this insect, which was predicted to develop through only one generation during the winter months of April to August in Johannesburg. A CLIMEX model also showed that cold stress limits the mirid's ability to overwinter in the interior of the country, while determination of the lower lethal limit (–3.5 °C) and critical thermal minimum (1.2 ± 1.17 °C) also indicated that extreme temperatures will limit establishment at certain sites. It is concluded that E. catarinensis is limited in its distribution in South Africa by low winter temperatures. 相似文献
1000.
T. Tvrdik Suzanne Marcus Sai-Mei Hou Susann Fält Peri Noori Natalia Podlutskaja Folker Hanefeld Petter Strømme Bo Lambert 《Human genetics》1998,103(3):311-318
Mutations identified in the hypoxanthine phosphoribosyltransferase (HPRT) gene of patients with Lesch-Nyhan (LN) syndrome
are dominated by simple base substitutions. Few hotspot positions have been identified, and only three large genomic rearrangements
have been characterized at the molecular level. We have identified one novel mutation, two tentative hot spot mutations, and
two deletions by direct sequencing of HPRT cDNA or genomic DNA from fibroblasts or T-lymphocytes from LN patients in five
unrelated families. One is a missense mutation caused by a 610C→T transition of the first base of HPRT exon 9. This mutation
has not been described previously in an LN patient. A nonsense mutation caused by a 508C→T transition at a CpG site in HPRT
exon 7 in the second patient and his younger brother is the fifth mutation of this kind among LN patients. Another tentative
hotspot mutation in the third patient, a frame shift caused by a G nucleotide insertion in a monotonous repeat of six Gs in
HPRT exon 3, has been reported previously in three other LN patients. The fourth patient had a tandem deletion: a 57-bp deletion
in an internally repeated Alu-sequence of intron 1 was separated by 14 bp from a 627-bp deletion that included HPRT exon 2 and was flanked by a 4-bp repeat.
This complex mutation is probably caused by a combination of homologous recombination and replication slippage. Another large
genomic deletion of 2969 bp in the fifth patient extended from one Alu-sequence in the promoter region to another Alu-sequence of intron 1, deleting the whole of HPRT exon 1. The breakpoints were located within two 39-bp homologous sequences,
one of which overlapped with a well-conserved 26-bp Alu-core sequence previously suggested as promoting recombination. These results contribute to the establishment of a molecular
spectrum of LN mutations, support previous data indicating possible mutational hotspots, and provide evidence for the involvement
of Alu-mediated recombination in HPRT deletion mutagenesis.
Received: 21 April 1998 / Accepted: 16 July 1998 相似文献