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21.
The catalytic action of dopamine beta-hydroxylase on 1-phenyl-1-propyne results in concomitant loss of enzyme activity. At pH 5.5 and 25 degrees C, 1-phenyl-1-propyne inactivates dopamine beta-hydroxylase in a mechanism-based fashion. The inactivation rate is first-order, follows saturation kinetics, and is strictly dependent on catalysis (oxygen and ascorbate are essential). The inactivation rate of saturating 1-phenyl-1-propyne (kinact) increases from 0.08 to 0.22 min-1 when the oxygen saturation increases from 21 to 100%, respectively. Inactivation also requires a copper-containing catalytically competent enzyme. Tyramine and norepinephrine (respectively, substrate and product of the normal catalytic reaction) protect against inactivation, and no regain of enzyme activity occurs after prolonged dialysis. Experiments with ether-extracted incubation solutions (+/- enzyme) showed no difference in their gas chromatography-mass spectral patterns implying that inactivation of dopamine beta-hydroxylase by 1-phenyl-1-propyne occurs through a kinetic process with a partition ratio (kcat/kinact) equal to or near 1. Thus, this acetylenic substrate analog appears to be a very efficient mechanism-based inhibitor of dopamine beta-hydroxylase. We propose that inactivation of this enzyme by 1-phenyl-1-propyne proceeds by formation of a reactive intermediate that occurs prior to product formation and that alkylates an amino acid residue at the active site of the enzyme. 相似文献
22.
Two crystal forms of calcium carbonate were observed: calcite (utricle) and aragonite (saccule, lagena, endolymphatic sac). The first step in otolith formation is the appearance of organic structures in the macula. The subsequent step is characterized by fast growing primitive crystals with a prismatic habitus that successively transform into adult or mature crystals. With the metamorphosis, the aragonite crystals of the endolymphatic organ show clear signs of erosion that can be related to a process of CaCO3 mobilization from such deposits. 相似文献
23.
Cristina Rinaldi-Garaci Enrico Garaci Vera Del Gobbo Cartesio Favalli Teresa Jezzi Allan L. Goldstein 《Cellular immunology》1983,80(1):57-65
The effects of thymosin-α1 on the stimulation of specific release of prostaglandin E2 (PGE2) from splenic lymphocytes and thymocytes were studied. Experiments were also performed to study in parallel the absolute levels of thymosin-α1 in the blood and the induction of serum FTS activity and of azathioprine sensitivity of spleen cells from adult thymectomized (ATx) mice. A significant difference in the release of PGE2 between normal splenocytes and splenocytes from ATx mice was observed. Thymosin-α1 at certain concentrations was able to stimulate PGE2 release from lymphocytes of ATx mice while inhibiting release in lymphocytes of normal mice. Also, thymocytes were stimulated to release PGE2 after incubation with α1 in a manner similar to that seen in spleen cells of ATx mice. Approximately the same concentration of α1 was found to also correct the low azathioprine sensitivity of splenocytes from ATx mice. Determinations of FTS-like activity in the blood and the pharmacokinetics of α1 after administration of this synthetic molecule show a clear dissociation. A maximum peak of α1 activity was obtained after 1 hr, while maximal FTS-like activity was observed after 24 hr. The inhibition of the induction by α1 of FTS-like activity and of Thy 1.2 antigen by indomethacin suggests that the action of α1 requires prostaglandin biosynthesis. 相似文献
24.
GTP gamma S stimulation of endosome fusion suggests a role for a GTP-binding protein in the priming of vesicles before fusion. 总被引:7,自引:1,他引:6 下载免费PDF全文
Guanosine 5'-(3-O-thio)triphosphate (GTP gamma S), a non-hydrolyzable analogue of GTP, inhibits in vitro fusion among early endocytic vesicles in the presence of high concentrations of cytosol. In this report we show that fusion is remarkably stimulated by GTP gamma S under conditions where cytosolic components are the limiting factors for the process. The amount of cytosolic factors required for maximal fusion activity is several-fold decreased by the presence of GTP gamma S. Moreover, preincubation of vesicles in the presence of cytosol and GTP gamma S allows fusion to proceed even in the absence of cytosol. Our results indicate that a GTP-binding protein facilitates the binding of cytosolic factor(s) required for endosome fusion to the endosomal membrane and stabilizes a dilution-resistant intermediate of the fusion process. 相似文献
25.
26.
A case of hereditary persistence of fetal hemoglobin caused by a gene not linked to the β-globin cluster 总被引:2,自引:0,他引:2
Summary The pattern of inheritance of several polymorphic restriction sites associated with the -gene cluster, and spanning a region of 52 kb, demonstrates that a determinant for hereditary persistence of fetal hemoglobin (HPFH) segregates independently from the non- globin gene cluster, as we postulated several years ago on purely genetical grounds. This finding provides additional evidence for the existence of diffusible factors affecting -chain expression. Moreover, we have identified a private HinccII polymorphism, in the vicinity of the gene in the family studied. 相似文献
27.
Elisabeth Oppliger Leibundgut Bendicht Wermuth Jean-Pierre Colombo Sabina Liechti-Gallati 《Human genetics》1996,97(2):209-213
Ornithine transcarbamylase (OTC) deficiency, the most common inborn error of the urea cycle, shows X-linked inheritance with frequent new mutations. Using polymerase chain reaction (PCR) amplification of the individual exons including adjacent intron sequences followed by direct sequencing of the amplimers we identified four new mutations affecting donor splice sites of introns 2, 5, 6, and 8. The mutation at the first position of intron 2 was a G to A exchange associated with acute neonatal hyperammonemia in a male patient at the age of 5 months. A G to C substitution in intron 5 was detected in a boy who developed 2 days after birth hypotonia, and respiratory distress, followed by severe hyperammonemia and terminal coma. The intron 6 mutation, a G to T substitution, was detected in a girl presenting with first episodes of vomiting and agitation at the age of 2 months. The mutation in intron 8, also a G to T transition, caused fatal hyperammonemia and early death at the age of 15 days in a male patient. We present four donor splice site mutations resulting in severe neonatal or very early onset of the disease in three boys and in one female patient. As the GT dinucleotide of the 5 donor splice site is invariant and required for correct splicing the described mutations may lead to improperly spliced mRNAs and aberrant gene products. 相似文献
28.
Lucia Rosaria De Vitis Andrea Tedde Francesca Vitelli Franco Ammannati Pasquale Mennonna Umberto Bigozzi Enrico Montali Laura Papi 《Human genetics》1996,97(5):632-637
Meningiomas are benign tumors of the central nervous system. They are usually sporadic but can also occur associated with the neurofibromatosis type 2 (NF2) syndrome. The gene responsible for NF2, recently isolated from chromosome 22, encodes a membrane-organizing protein that shows high sequence homology to a protein family thought to link the cytoskeleton with membrane proteins. Mutations of the NF2 gene have been described in sporadic meningiomas, exclusively in tumors that show loss of heterozygosity (LOH) of 22q. These preliminary results indicate that the NF2 gene is involved in the pathogenesis of at least a subset of meningiomas, where it does indeed behave as a tumor suppressor gene. In order to characterize better the role of the NF2 gene in the genesis of meningiomas we have examined the entire coding sequence of the gene in 125 meningiomas by single-strand conformational polymorphism analysis; furthermore, LOH analysis for markers of 22q has been carried out. Inactivating mutations were identified in 30% of our samples, all of which also showed LOH of 22q. The majority of mutations identified were frameshifts and nonsense mutations, which are predicted to produce a truncated or non-functional protein. We also found two missense and three in-frame deletions that may pinpoint specific regions of the protein critical to its function. Furthermore, the distribution of mutations throughout the gene, suggested that exons 2, 3, 5, 11 and 13 are more frequently involved. Our results reconfirm the importance of the NF2 gene in the pathogenesis of meningiomas and also suggest that there may be a nonrandom clustering of mutations throughout the gene. 相似文献
29.
“Bacillus thermoantarcticus” sp. nov., from Mount Melbourne,Antarctica: a novel thermophilic species
B. Nicolaus Licia Lama Enrico Esposito Maria Cristina Manca Guido di Prisco Agata Gambacorta 《Polar Biology》1996,16(2):101-104
A novel thermophilic Gram-positive bacillus, “Bacillus thermoantarcticus”, isolated from geothermal soil near the crater of Mount Melbourne, is described. The organism grows at an optimal temperature
of 63°C at pH 6.0, is oxidase-positive, catalase-negative and produces an exopolysaccharide, an exocellular xylanase, an intracellular
alcohol dehydrogenase and exo- and endocellular α-glucosidase(s). The sequence of 16S rDNA is very similar to that of “Bacillus thermoglucosidasius”; however, the guanine-plus-cytosine (G+C) content is 8 mol% higher. The type strain is “Bacillus thermoantarcticus” (DSM 9572).
Received : 3 February 1995/Accepted : 12 May 1995 相似文献
30.
Giovanna Zolese Ileana Giambanco Giovanna Curatola Roberto Staffolani Enrico Gratton Rosario Donato 《Cell calcium》1996,20(6):465-474
Phase-modulation fluorescence lifetime measurements were used to study the single Trp residue of the Ca2+-binding protein S-100a both in the absence and in the presence of Ca2+ and/or Mg2+. Trp fluorescence decay for the protein was satisfactorily described by Lorentzian lifetime distributions centered around two components (approximately 4 ns and 0.5 ns). Lifetime values were unchanged by 2 mM Ca2+, but the fractional intensity associated with longer lifetime increased up to 75%. In the presence of Mg2+, the Ca2+ induced increase of the fractional intensity associated with longer lifetime was only 57%. For the protein in buffer, about the 85% of the recovered anisotropy was associated to a rotational correlation time of 6.7 ns. After the addition of Ca2+, this value was increased to 16.08 ns. In the presence of Mg2+, Ca+2 increased the rotational correlation time to 33.75 ns. Similar studies were performed with S-100a interacting with egg phosphatidylcholine vesicles (SUV). Our data suggest that the conformation of the protein may be influenced by structural features of the lipidic membrane. Moreover, data obtained in the presence of Mg2+ indicate some interaction between lipids and S-100, likely mediated by this ion. 相似文献