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61.
Antonio Cupane Eugenio Vitrano Pal Ormos G.Ulrich Nienhaus 《Biophysical chemistry》1996,60(3):111-117
We have measured the Soret band of the photoproduct obtained by complete photolysis of sperm whale carbonmonoxymyoglobin at 10 K. The experimental spectrum has been modeled with an analytical expression that takes into account the homogeneous bandwidth, the coupling of the electronic transition with both high and low frequency vibrational modes, and the effects of static conformational heterogeneity. The comparison with deoxymyoglobin at low temperature reveals three main differences. In the photoproduct, the Soret band is shifted to red. The band is less asymmetric, and an enhanced coupling to the heme vibrational mode at 674 cm−1 is observed. These differences reflect incomplete relaxation of the active site after ligand dissociation. The smaller band asymmetry of the photoproduct can be explained by a smaller displacement of the iron atom from the mean porphyrin plane, in quantitative agreement with the X-ray structure analysis. The enhanced vibrational coupling is attributed to a subtle heme distortion from the planar geometry that is barely detectable in the X-ray structure. 相似文献
62.
Alessandro Stefani Antonio Pisani Nicola B. Mercuri Paolo Calabresi 《Molecular neurobiology》1996,13(1):81-95
Glutamatergic transmission in the central nervous system (CNS) is mediated by ionotropic, ligand-gated receptors (iGluRs), and metabotropic receptors (mGluRs). mGluRs are coupled to GTP-binding regulatory proteins (G-proteins) and modulate different second messenger pathways. Multiple effects have been described following their activation; among others, regulation of fast synaptic transmission, changes in synaptic plasticity, and modification of the threshold for seizure generation. Some of the major roles played by the activation of mGluRs might depend on the modulation of high-voltage-activated (HVA) calcium (Ca2+) currents. Some HVA Ca2+ channels (N-, P-, and Q-type channels) are signaling components at most presynaptic active zones. Their mGluR-mediated inhibition reduces synaptic transmission. The interference, by agonists at mGluRs, on L-type channels might affect the repetitive neuronal firing behavior and the integration of complex events at the somatic level. In addition, the mGluR-mediated effects on voltagegated Ca2+ signals have been suggested to strongly influence neurotoxicity. Rather different coupling mechanisms underlie the relation between mGluRs and Ca2+ currents: Together with a fast, membrane-delimited mechanism of action, much slower responses, involving intracellular second messengers, have also been postulated. In the recent past, the relative paucity of selective agonists and antagonists for the different subclasses of mGluRs had hampered the clear definition of the roles of mGluRs in brain function. However, the recent availability of new pharmacological tools is promising to provide a better understanding of the neuronal functions related to different mGluR subtypes. The analysis of the mGluR-mediated modulation of Ca2+ conductances will probably offer new insights into the characterization of synaptic transmission and the development of neuroprotective agents. 相似文献
63.
Eitel Pastor Cristina Otero Antonio Ballesteros 《Biocatalysis and Biotransformation》1995,12(2):147-157
Mixtures of 1(3)-monostearin and distearin were prepared by direct esterification of glycerol with stearic acid or transesterification using ethyl stearate as acyl donor in the presence of Candida antarctica lipase (Novozym 435) using a variety of solvents of differing polarity. In all cases, the transesterification resulted in higher product yields. In n-heptane as reaction medium the addition of water (3%) was essential for high product yields, with mono- and distearin being produced in almost equal amounts. Using more polar solvents as reaction media, such as acetonitrile or acetone, again the highest yields were obtained in the transesterification mode; employing these solvents the reactions were much more selective towards the formation of monostearin. 相似文献
64.
Dr. Federico Carbone Prof. Dr. Ruggero Matteucci Dr. Brian R. Rosen Prof. Dr. Antonio Russo 《Facies》1994,30(1):1-13
Summary From a study of two areas, Jesira and the Bajuni Archipelago, about 400 km apart, a general pattern can be established for
the Recent facies, together with the morphological and taxonomic features of the corals. Present day coral development is
characterized by true fringing reefs in the Bajuni Archipelago and by scattered patches and knolls in the Jesira area. The
coral fauna, consisting of 27 genera and 63 species so far (including all uncertainties, but not sight records), is rather
poor, though coral communities are locally well developed. These figures probably reflect incomplete study and sampling. Although
comparison with other areas may therefore be premature, a preliminary biogeographical analysis suggests that this fauna is
more closely related to that of the Red Sea than to East Africa and the Seychelles. This differs from other published biogeographical
work on Indian Ocean coral faunas, but further study of the corals in this and neighbouring areas of the Indian Ocean is needed
in order to resolve this apparent anomaly. 相似文献
65.
Giuliano Callaini Maria Giovanna Riparbelli Marcella Cintorino Sergio Antonio Tripodi Giorgio Bianciardi Piero Tosi Romano Dallai 《Biology of the cell / under the auspices of the European Cell Biology Organization》1994,81(1):39-45
Summary— Immunofluorescence and immunoelectron microscopy indicated that the antibody raised against the nuclear antigen Ki-67 of mammalian cells recognized antigenic determinants of early Drosophila embryos, localized on the outside of the nuclear envelope. Hence, the nuclear envelope of Drosophila appears to share a similar epitope with the chromosome scaffold of mitotic mammalian cells. With the progression of mitosis the antigen persisted around the mitotic spindle region and was also found in the pole regions at metaphase and anaphase. The antibody also stained the equatorial regions of the spindles from anaphase to late telophase. The antibody may therefore be used as a biochemical marker of the nuclear envelope for studying nuclear membrane biogenesis and behavior during the mitotic divisions of the Drosophila embryo. 相似文献
66.
In the former part of the review the principal available data aboutHox genes, their molecular organisation and their expression in vertebrate embryos, with particular emphasis for mammals, are briefly summarized.In the latter part we analysed the expression of four mouse homeobox genes related to twoDrosophila genes expressed in the developing head of the fly: Emx1 and Emx2, related toems, and Otx1 and Otx2, related tootd. 相似文献
67.
Antonio Cuadrado Wolfgang Issing Timothy P. Fleming Christopher J. Molloy 《Journal of cellular physiology》1994,159(3):434-440
Protein kinase C (PKC) represents a family of structurally related Ser/Tre kinases which are involved in mitogenic signalling and may contribute to human neoplasia. To address this issue, the messenger RNA and protein levels of PKC isoenzymes α and β were analyzed in several human sarcoma- and carcinoma-derived cell lines. Carcinomas contained low or undetectable levels of either PKC-α or PKC-β. Sarcomas exhibited similar or increased PKC expression compared to human diploid fibroblasts. Moreover, sarcoma cell lines expressing one PKC isoform did not contain detectable levels of the other. When PKC was depleted from the tumor cells, we observed that the PKC overexpressing sarcomas had reduced their malignant properties as determined by their ability to grow in semisolid medium. In addition, epidermal growth factor-stimulated and erbB2-transformed fibroblasts exhibited enhanced cell growth in the absence of PKC. We propose a model for the effect of PKC as a negative regulator of proliferation in epithelial cells and a growth promoter in fibroblasts. © 1994 wiley-Liss, Inc. 相似文献
68.
Gabriel Gutiérrez Josep Casadesús Jose L. Oliver Antonio Marine 《Journal of molecular evolution》1994,39(4):340-346
E. coli genes that contain a high frequency of the tetranucleotide CTAG are also rich in the tetramers CTTG, CCTA, CCAA, TTGG, TAGG, and CAAG (group-I tetramers). Conversely, E. coli genes lacking CTAG are rich in the tetranucleotides CCTG, CCAG, CTGG, and CAGG (group-II tetramers). These two gene samples differ also in codon usage, amino acid composition, frequency of Dcm sites, and contrast vocabularies. Group-I tetramers have in common that they are depleted by very-short-patch repair (VSP), while group-II tetramers are favored by VSP activity. The VSP system repairs G:T mismatches to G:C, thereby increasing the overall G+C content of the genome; for this reason the CTAG-rich sample has a lower G+C content than the CTAG-poor sample. This compositional heterogeneity can be tentatively explained by a low level of VSP activity on the CTAG-rich sample. A negative correlation is found between the frequency of group-I tetramers and the level of gene expression, as measured by the Codon Adaptation Index (CAI). A possible link between the rate of VSP activity and the level of gene expression is considered.Correspondence to: A. Marine 相似文献
69.
Villalba J. M. Navarro F. Roldán J. M. González-Reyes J. A. Navas P. 《Protoplasma》1994,178(3-4):87-96
Summary Expression of various sugar residues on the plasma membrane of frog (Rana perezi) epidermal cells at different stages of differentiation has been monitored with the use of a battery of HRP-conjugated lectins. In paraffin-embedded tissue, mannose residues (stained by Concanavalin A) were detected at the keratinocyte cell surface in all epidermal strata. However,Lens culinaris agglutinin (LCA), also specific for mannose, specifically stained the plasma membrane of cells from the stratum germinativum. Expression of N-acetyl-glucosamine (GlcNAc), labelled with wheat germ agglutinin (WGA), was maximum at the cell surface of basal cells and progressively decreased through the stratum spinosum. Galactose (Gal) and N-acetyl-galactosamine (GalNAc) residues, labelled withGriffonia simplicifolia I (GS I) andGlycine max (SBA) agglutinins, respectively, were expressed according to the degree of differentiation in amphibian epidermal cells. Sialic acid-containing glycoproteins, labelled withLimax flavus agglutinin (LFA), were found in the outermost plasma membrane of the replacement cell layer and stratum corneum. Glycoproteins responsible for the observed lectin-binding patterns have been identified by staining on nitrocellulose filters after electrophoresis of solubilized plasma membrane fractions and Western blotting. Changes at the level of glycosylation of plasma membrane glycoproteins as epidermal cells differentiate are discussed on the basis of a progressive addition of Gal residues. Integral membrane proteins have been solubilized with the non-denaturing detergent CHAPS and glycoproteins containing terminal Gal residues, that are expressed according to the degree of differentiation in frog epidermis, have been partially purified by affinity chromatography on a GS I-Sepharose 4 B column. The purified fraction was composed by four acidic glycoproteins with isoelectric points between 4.6 and 5.2 and, in SDS-gels gave five major protein bands with approximate molecular weights of 148, 140, 102, 60, and 52 kDa in SDS-gels. The 102 and 52 kDa bands correspond to the a and subunits of amphibian epidermal Na+,K+-ATPase as demonstrated by specific staining with a polyclonal antibody against the catalytic subunit of pig kidney proton pump and staining with lectins GS I, GS II, and WGA. Possible relationships between higher molecular weight proteins and the constituents of intramembranous particles from the outermost plasma membranes of the replacement cell layer and the stratum corneum are also discussed.Abbreviations BSA
bovine serum albumin
- CHAPS
(3-[(cholamidopropyl) dimethyl-ammonio] 1-propanesulfonate)
- Con A
Canavalia ensiformis agglutinin
- DTT
dithiothreitol
- Gal
galactose
- GalNAc
N-acetyl-D-galactosamine
- GlcNAc
N-acetyl-D-glucosamine
- GS I
Griffonia simplicifolia agglutinin I
- GS II
Griffonia simplicifolia agglutinin II
- HRP
horseradish peroxidase
- LFA
Limax flavus agglutinin
- LCA
Lens culinaris agglutinin
- NDPAGIF
non-denaturing polyacrylamide gel isoelectric focusing
- PAGE
polyacrylamide gel electrophoresis
- PAP
peroxidase-antiperoxidase
- PBS
phosphate buffered saline
- PMSF
phenyl methyl sulphonyl fluoride
- RCL
replacement cell layer
- SBA
soybean agglutinin (Glycine max)
- SB
stratum basal
- SDS
sodium dodecyl sulphate
- SG
stratum granulosum
- SS
stratum spinosum
- UEA I
Ulex europaeus agglutinin I
- WGA
wheat germ (Triticum vulgaris) agglutinin 相似文献
70.