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21.
Maria Giovanna Riparbelli Romano Dallai Giuliano Callaini 《Biology of the cell / under the auspices of the European Cell Biology Organization》1993,78(3):223-227
Rhodamine phalloidin-staining was used to study the organization of the cortical actin cytoskeleton of the early Ceratitis capitata embryo. The dynamics of the actin aggregates and their changes in distribution during the formation of the syncytial blastoderm, were followed in detail. It was found that these aggregates formed a shell-like cluster around the interphase nuclei, and concentrated toward the poles of the mitotic apparatus when the nuclei divided. Laser scanning confocal microscopy revealed that aggregates not clustered at the poles of the mitotic apparatus were closely associated with fine fibers of a dense cytoplasmic network of actin filaments. 相似文献
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Giovanna Berruti 《Molecular reproduction and development》1994,38(4):386-392
The majority of cellular responses to changing environmental conditions is regulated by protein kinases. Spermatozoa have many special properties, including motility with demonstrated chemotaxis, the ability to undergo capacitation, and the acrosome reaction, which are in part controlled by extracellular signals and in which sperm kinases are considered to be involved. We have previously reported that there is a protein kinase activity, which phosphorylates the synthetic substrate poly-(Glu, Tyr) with a Km value of 2.3 μM, and is inhibited by the tyrosine kinase inhibitor tyrphostin, in the protein extract from boar spermatozoa (Berruti and Porzio, 1992: Biochim Biophys Acta 1118:149–154). Now we have demonstrated that the enzyme is cytosolic, is active as a monomer of Mr 42,000, is stimulated by Mg2+ > Mn2+ but not by Ca2+, is renaturable, and can phosphorylate native protein substrates such as microtubule-associated protein 2 (MAP2) and histone H2B both on the tyrosine and serine residues. N-terminal sequence analysis suggests that it is a novel protein. These new findings imply that the boar sperm 42 kD kinase may be a novel member of the emerging class of dual-specificity protein kinases, and they raise the intriguing question of its function in the protein kinase network mediating signal transduction in mammalian spermatozoa. © 1994 Wiley-Liss, Inc. 相似文献
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Giovanna Belmonte Cecilia Pederzolli Peter Maček Gianfranco Menestrina 《The Journal of membrane biology》1993,131(1):11-22
Summary The interaction ofActinia equina equinatoxin II (EqT-II) with human red blood cells (HRBC) and with model lipid membranes was studied. It was found that HRBC hemolysis by EqT-II is the result of a colloid-osmotic shock caused by the opening of toxin-induced ionic pores. In fact, hemolysis can be prevented by osmotic protectants of adequate size. The functional radius of the lesion was estimated to be about 1.1 nm. EqT-II increased also the permeability of calcein-loaded lipid vesicles comprised of different phospholipids. The rate of permeabilization rised when sphingomyelin was introduced into the vesicles, but it was also a function of the pH of the medium, optimum activity being between pH 8 and 9; at pH 10 the toxin became markedly less potent. From the dose-dependence of the permeabilization it was inferred that EqT-II increases membrane permeability by forming oligomeric channels comprising several copies of the cytolysin monomer. The existence of such oligomers was directly demonstrated by chemical cross-linking. Addition of EqT-II to one side of a planar lipid membrane (PLM) increases the conductivity of the film in discrete steps of defined amplitude indicating the formation of cation-selective channels. The conductance of the channel is consistent with the estimated size of the lesion formed in HRBC. High pH and sphingomyelin promoted the interaction even in this system. Chemical modification of lysine residues or carboxyl groups of this protein changed the conductance, the ion selectivity and the current-voltage characteristic of the pore, suggesting that both these groups were present in its lumen. 相似文献
25.
Biometric Study of Acetoin Production in Hanseniaspora guilliermondii and Kloeckera apiculata 下载免费PDF全文
Patrizia Romano Giovanna Suzzi Roberto Zironi Giuseppe Comi 《Applied microbiology》1993,59(6):1838-1841
Gas chromatographic analysis by direct injection of samples yielded quantitative data on acetoin content. Ninety-six strains of Hanseniaspora guilliermondii and Kloeckera apiculata were investigated for the ability to produce acetoin in synthetic medium and in must. High-level production of acetoin was found to be a characteristic of both species. In synthetic medium, the two species were not significantly different with respect to sugar utilization and ethanol or acetoin production. In grape must, the two species were significantly different (P = 0.001) in acetoin production and K. apiculata exhibited a significantly negative correlation between acetoin production and either sugar consumption or ethanol production. Use of selected apiculate yeasts in mixed cultures with Saccharomyces cerevisiae seems promising for optimization of wine bouquet. 相似文献
26.
Giovanna Cacciapuoti Maria Angela Moretti Sabrina Forte Assunta Brio Laura Camardella Vincenzo Zappia Marina Porcelli 《European journal of biochemistry》2004,271(23-24):4834-4844
The extremely heat-stable 5'-methylthioadenosine phosphorylase from the hyperthermophilic archaeon Pyrococcus furiosus was cloned, expressed to high levels in Escherichia coli, and purified to homogeneity by heat precipitation and affinity chromatography. The recombinant enzyme was subjected to a kinetic analysis including initial velocity and product inhibition studies. The reaction follows an ordered Bi-Bi mechanism and phosphate binding precedes nucleoside binding in the phosphorolytic direction. 5'-Methylthioadenosine phosphorylase from Pyrococcus furiosus is a hexameric protein with five cysteine residues per subunit. Analysis of the fragments obtained after digestion of the protein alkylated without previous reduction identified two intrasubunit disulfide bridges. The enzyme is very resistant to chemical denaturation and the transition midpoint for guanidinium chloride-induced unfolding was determined to be 3.0 M after 22 h incubation. This value decreases to 2.0 M in the presence of 30 mM dithiothreitol, furnishing evidence that disulfide bonds are needed for protein stability. The guanidinium chloride-induced unfolding is completely reversible as demonstrated by the analysis of the refolding process by activity assays, fluorescence measurements and SDS/PAGE. The finding of multiple disulfide bridges in 5'-methylthioadenosine phosphorylase from Pyrococcus furiosus argues strongly that disulfide bond formation may be a significant molecular strategy for stabilizing intracellular hyperthermophilic proteins. 相似文献
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Leirla Salazar Hafida Fsihi Edda de Rossi Giovanna Riccardi Carmen Rios Stewart T. Cole Howard E. Takiff 《Molecular microbiology》1996,20(2):283-293
The genus Mycobacterium is composed of species with widely differing growth rates ranging from approximately three hours in Mycobacterium smegmatis to two weeks in Mycobacterium leprae. As DNA replication is coupled to cell duplication, it may be regulated by common mechanisms. The chromosomal regions surrounding the origins of DNA replication from M. smegmatis, M. tuberculosis, and M. leprae have been sequenced, and show very few differences. The gene order, rnpA-rpmH-dnaA-dnaN-recF-orf-gyrB-gyrA, is the same as in other Gram-positive organisms. Although the general organization in M. smegmatis is very similar to that of Streptomyces spp., a closely related genus, M. tuberculosis and M. leprae differ as they lack an open reading frame, between dnaN and recF, which is similar to the gnd gene of Escherichia coli. Within the three mycobacterial species, there is extensive sequence conservation in the intergenic regions flanking dnaA, but more variation from the consensus DnaA box sequence was seen than in other bacteria. By means of subcloning experiments, the putative chromosomal origin of replication of M. smegmatis, containing the dnaA-dnaN region, was shown to promote autonomous replication in M. smegmatis, unlike the corresponding regions from M. tuberculosis or M. leprae. 相似文献
29.
Early in development the precursors of germ cells in Drosophila migrate at the posterior pole of the embryo and translocate to the bottom of the developing posterior midgut primordium. At the end of germ band elongation the pole cells cross the gut wall to enter in association with the gonadal mesoderm. We used laser scanning confocal microscopy on whole-mount Rh-phalloidin-stained embryos and transmission electron microscopy to investigate how pole cells cross the epithelial wall of the posterior midgut primordium. Our results suggest that pole cells leave the midgut sac by traveling through the intercellular spaces of the epithelium. During this process the epithelial cells at the bottom of the posterior midgut primordium are greatly deformed, but their junctional complexes do not completely release, avoiding breaks in the epithelial wall. 相似文献
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