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41.
The urea-degrading enzyme of Cyclotella cryptica was testedin crude cell-free extracts for effects from chemical reagentsknown to distinguish between urease and ATP:urea amidolyase.Inhibition of the enzyme by hydroxyurea and its indifferenceto added ATP, Mg2+ or K+ avidin or biotin clearly characterizedthe enzyme as urease (EC 3.5.1.5
[EC]
). The Cyclotella urease wasunaffected by thiourea addition, as was also the growth of thediatom in the presence of this substrate analogue. Indirectevidence was obtained from growth studies of the diatom andcorresponding urease production showing that the enzyme: (i)contains Ni2+ tightly bound to an apoprotein; (ii) is producedconstitutively even from growth on nitrate and does not requireextracellular urea for its synthesis, although quantitativelythe activity is greatest from growth on urea. It is concludedthat Cyclotella urease is a Ni2+ constitutive enzyme similarin many respects to those previously reported from Phaeodactylumtricornutwn and Tetraselmis maculata. 相似文献
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45.
Trypanosoma cruzi: 4-aminopyrazolopyrimidine in the treatment of experimental Chagas' disease 总被引:1,自引:0,他引:1
JoséLuis Avila Angela Avila Edgar Mun̄oz Héctor Monzón 《Experimental parasitology》1983,56(2):236-240
An allopurinol metabolite, 4-aminopyrazolopyrimidine, was tested on two different strains of mice (NMRI-IVIC and C57Bl/6J) that had been infected 4 days earlier with the virulent Ya strain of Trypanosoma cruzi. Low doses of 4-aminopyrazolopyrimidine (0.125-0.500 mg/kg body wt/day) for 10 days induced a significant reduction in parasitemia (direct counts and subinoculation experiments) and increased survival time (without any evidence of toxicity) compared with untreated animals. When tested in vitro, 4-aminopyrazolopyrimidine was sixfold more active than allopurinol as a trypanostatic drug. The low therapeutic doses of 4-aminopyrazolopyrimidine suggest that this drug may be useful in the treatment of acute Chagas' disease. 相似文献
46.
Luis A. Marky Kenneth S. Blumenfeld Sharon Kozlowski Kenneth J. Breslauer 《Biopolymers》1983,22(4):1247-1257
Differential scanning calorimetry (DSC), temperature-dependent uv-absorption spectroscopy, and temperature-dependent CD were used to monitor and characterize the salt-dependent, thermally induced structural transitions in the deoxydodecanucleotide d(CGCGAATTCGCG). At the high oligomer concentrations required for DSC, the calorimetric scans revealed a single, monophasic transition curve at all salt concentrations. Based on previous nmr melting studies under similar conditions, we conclude that these monophasic transitions correspond to the cooperative duplex-to-single-strand conversion of the dodecamer. By contrast, at the lower oligomer concentrations used for the spectroscopic studies, the shapes of the uv and CD melting curves were found to depend on the concentration of the added salt. At high salt (≥0.1M Na+), a single, monophasic transition curve was observed. At lower salt (?0.01M Na+), the CD and uv melting curves exhibit biphasic behavior. Based on the concentration dependence, the enthalpy, and the cooperativity of each transition in the biphasic curve, we conclude that at low salt and low oligomer concentrations, the dodecamer melts in a sequential manner involving initial disruption of a duplex structure and subsequent disruption of a hairpin structure. 相似文献
47.
Alicia Mimbrera Luis Rivas Faustino Mollinedo Emilio Muñoz Vicente Larraga 《Molecular and cellular biochemistry》1983,56(1):73-80
Summary The combined use of proteolytic digestion and lactoperoxidase catalyzed labelling with [125I] applied to membrane-bound or soluble pure F1-ATPase from Micrococcus lysodeikticus has allowed us to establish the topography of its , , and subunits within the protein molecule and with respect to the plane of the membrane.The subunit is most externally located to the membrane bilayer looking towards the cytoplasmic face, a position consistent with its proposed catalytic role. The and subunits lie in an intermediate layer between the subunits and the membrane, in which the subunit occupies a central position within the F1-ATPase molecule in contact with the subunit. The subunit appears to be tightly bound to the F0 component of the ATPase complex, probably buried in the membrane bilayer. A molecular arrangement of M. lysodeikticus ATPase is proposed that, taking into account the subunit stoichiometry 3 3 2 2 (MW 420 000), accommodates the role assigned to each subunit and most, if not all, the known properties of this bacterial energy-transducing protein. 相似文献
48.
Comparative DNA-RNA hybridization in differentiated cells 总被引:1,自引:0,他引:1
49.
Development of Competence in Thymine-starved Bacillus subtilis with Chromosomes Arrested at the Terminus 总被引:3,自引:2,他引:1
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Tryptophan- and thymine-requiring cells of Bacillus subtilis, emerging from an amino acid starvation treatment which causes arrest of the chromosomes at the terminus, were not transformable. During subsequent incubation in a thymineless medium supplemented with amino acids, the cultures developed competence while retaining chromosome arrest. The competent subpopulation apparently shares the synchronous chromosome arrest of the bulk population. This was shown by different methods. The principal method was marker frequency analysis of the deoxyribonucleic acid extracted from a population enriched for competent cells by a column-chromatographic method. It is concluded that development of the competent state can occur in nondividing cells, and that the presence of a replication fork actively engaged in synthesis of deoxyribonucleic acid is not required for the development of this state. 相似文献
50.
Endothelial and leukocyte forms of IL-8. Conversion by thrombin and interactions with neutrophils 总被引:22,自引:0,他引:22
C A Hébert F W Luscinskas J M Kiely E A Luis W C Darbonne G L Bennett C C Liu M S Obin M A Gimbrone J B Baker 《Journal of immunology (Baltimore, Md. : 1950)》1990,145(9):3033-3040
We have recently shown that endothelial cell-derived IL-8 inhibits neutrophil adhesion to IL1-beta-activated human umbilical vein endothelial cell monolayers. IL-8 secreted by T lymphocytes or monocytes has been characterized as a promoter of neutrophil degranulation and chemotaxis. The IL-8 isolated from each of these cell types is a mixture of two IL-8 polypeptides, one consisting of 72 amino acids (herein called [ser-IL-8]72) and the other 77 amino acids (an N-terminal extended form herein called [ala-IL-8]77). IL-8 derived from T lymphocytes and monocytes is predominantly [ser-IL-8]72, whereas endothelial-derived IL-8 is highly enriched (greater than 80%) in [ala-IL-8]77. We address the relationship and activities of these two forms of IL-8 using recombinant proteins expressed by both mammalian cells and Escherichia coli. Thrombin was found to efficiently convert [ala-IL-8]77 to [ser-IL-8]72. In contrast, urokinase and tissue-type plasminogen activator were unable to cleave [ala-IL-8]77, and trypsin generated multiple IL-8 cleavage fragments. In competitive binding assays using 125I[ala-IL-8]77 neutrophils exhibited a twofold preference for [ser-IL-8]72 over [ala-IL-8]77. Both forms of IL-8 inhibited neutrophil adhesion to IL-1-beta-activated HUVEC monolayers by up to 90%. However, [ser-IL-8]72 was approximately 10-fold more potent than [ala-IL-8]77 in these assays (ED50 approximately 0.3 nM for [ser-IL-8]72 vs approximately 3 nM for [ala-IL-8]77. Both forms of IL-8 promoted degranulation of cytochalasin B-treated neutrophils [[ser-IL-8]72 (ED50 greater than 10 nM) was two- to three-fold more potent than [ala-IL-8]77], although in this regard they were less active than FMLP. Our data suggest that [ala-IL-8]77 and [ser-IL-8]72 have qualitatively similar and potentially complex biological activities, and that full activation of IL-8 requires cleavage to the [ser-IL-8]72 form. In the case of inflamed endothelial cells this activation could be mediated by thrombin generated in the procoagulant environment associated with these cells. 相似文献