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1.
The role of the polypeptide matrix in electron transfer processes in proteins has been studied in two distinct systems: first
in a protein where the induced ET is artificial, and second as part of the catalytic cycle of an enzyme. Azurins are structurally
well-characterized blue single-copper proteins consisting of a rigid β-sheet polypeptide matrix. We have determined rate constants
and activation parameters for intramolecular long-range electron transfer between the disulfide radical anions (generated
by pulse radiolysis) and the copper(II) centre as a function of driving force and nature of the intervening medium in a large
number of wild-type and single-site-mutated proteins. In ascorbate oxidase, for which the three-dimensional structure is equally
well characterized, the internal ET from the type-I Cu(I) to the trinuclear Cu(II) centre has been studied. We find that the
results correlate well with distance through well-defined pathways using a through-bond electron tunnelling mechanism.
Received: 2 January 1997 / Accepted: 6 February 1997 相似文献
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M Denechaud J M Israel F Belloc J D Vincent 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1987,304(16):427-431
The different antehypophysical cell types which synthetize and release somatotroph (GH), corticothroph (ACTH), gonadotroph (LH-FSH) and lactotroph (PRL) hormones were analysed. The experiments were performed on hypophyses from five groups of animals: adult males, 14 days-old female, adult females, gestating adult females and lactating adult females. The cells were analysed by immunofluorescence using flow cytometry. For each of the hormones studied, there was a characteristic spectral distribution of cells. The evolution of cell size and granular content with respect to sex and physiological state of each group was studied by the analysis of diffused light. Small, slightly granular cells represented 50% of the cell population in males and 14 day-old females but only 8% in gestating or lactating females. The study of the cell cycle showed the presence of dividing cells in the population of large, granular cells from gestating and from lactating females. No features of cell division were observed in the population of small, slightly granular cells. This study indicates the potential value of multiparametric analysis in the separation of pure sub-populations of antehypophysial cells. 相似文献
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Recognition of Superior Photosynthetic Efficiency in the Field Using the CO(2)-Depletion Technique 下载免费PDF全文
The relationship between CO2 exchange rate (CER) and growth of crops in the field was investigated in Connecticut Broadleaf tobacco (Nicotiana tabacum) using the CO2-depletion technique. A particular objective was to determine if modest (i.e. <10%) varietal differences could be distinguished in mean CER. Statistical analysis of numerous CER values obtained over a wide range of irradiances during the course of the season indicated that differences of as little as 7% in the mean CER between varieties would be significant (n ~400). The usefulness of the CO2-depletion technique in detecting modest differences in photosynthetic efficiency has thus been demonstrated. These results are discussed in relation to the prospects for introducing and detecting genetic traits which would diminish photorespiration and increase CER and growth. 相似文献
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H Israel 《American journal of physical anthropology》1968,29(2):287-294
Microdensitometric analysis of a radiographic image of mineralized tissue offers information on the morphologic characteristics of the specimen examined. The use of microstructure (such as individual trabecula of bone) and macrostructure (such as Harris lines of arrest) as in vivo bone markers allows for assessment of gross skeletal changes in nondestructive fashion. This technique is also applicable to the study of the interrelationship of tooth and bone. In addition, microdensitometry offers precise information on the fine structure of bone as regards the trabecular elements. This technique is applicable in determining the size and quantity of trabeculae, their persistence over long periods of time, and the factors responsible for change or lack of change in trabeculae during growth and aging. 相似文献
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D E Feltner M Cooper J Weber M A Israel C J Thiele 《Journal of immunology (Baltimore, Md. : 1950)》1989,143(12):4292-4299
We have evaluated the relationship between the neuronal myc gene (NMYC) and class I major histocompatibility complex (MHC) expression in human neuroblastoma (NB) tumor cell lines. Class I MHC surface Ag expression in NB cell lines varied from nearly undetectable to levels nearly as high as in a lymphoblastoid cell line. Class I MHC mRNA levels in NMYC-amplified NB cell lines were lower than levels observed in single copy NMYC NB cell lines. However, considerable variation in class I MHC surface Ag and mRNA expression was evident in NMYC-amplified cell lines. To determine directly whether NMYC might modulate class I MHC expression in NB, we transfected a plasmid containing a recombinant NMYC gene into two tumor cell lines derived from a NB and a related neuroepithelioma tumor. Constitutive overexpression of the recombinant NMYC gene produced no consistent change in class I MHC surface Ag or mRNA levels. To determine whether class I MHC expression might be developmentally regulated in adrenal medullary cells, the precursor cells of adrenal NB tumors, beta 2-microglobulin expression was measured in fetal and adult adrenal glands. beta 2-Microglobulin expression was not evident in the neuroblasts of a 24-wk-old fetal adrenal gland, whereas beta 2-microglobulin expression was present in the adult adrenal medulla. These data suggest that variation in class I MHC expression among NB cells may reflect the developmental stage at which neuroblasts were arrested during tumorigenesis. 相似文献
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