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11.
The liver plays a key role in removing harmful chemicals from the body and is therefore often the first tissue to suffer potentially adverse consequences. To protect public health it is necessary to quantitatively estimate the risk of long-term low dose exposure to environmental pollutants. Animal testing is the primary tool for extrapolating human risk but it is fraught with uncertainty, necessitating novel alternative approaches. Our goal is to integrate in vitro liver experiments with agent-based cellular models to simulate a spatially extended hepatic lobule. Here we describe a graphical model of the sinusoidal network that efficiently simulates portal to centrilobular mass transfer in the hepatic lobule. We analyzed the effects of vascular topology and metabolism on the cell-level distribution following oral exposure to chemicals. The spatial distribution of metabolically inactive chemicals was similar across different vascular networks and a baseline well-mixed compartment. When chemicals were rapidly metabolized, concentration heterogeneity of the parent compound increased across the vascular network. As a result, our spatially extended lobule generated greater variability in dose-dependent cellular responses, in this case apoptosis, than were observed in the classical well-mixed liver or in a parallel tubes model. The mass-balanced graphical approach to modeling the hepatic lobule is computationally efficient for simulating long-term exposure, modular for incorporating complex cellular interactions, and flexible for dealing with evolving tissues. 相似文献
12.
Antikinetochore immunofluorescence staining has been used in several studies to determine whether a second kinetochore is present, active, or both, in multicentric chromosomes. All of these studies have used tissue culture cells, and contended with the problem of obtaining well spread, banded metaphase chromosomes without affecting the kinetochore staining. We have adapted hypotonic, centrifugation and chromosome staining techniques to obtain simultaneous Q-banding and bright kinetochore staining of chromosomes from human lymphocytes. 相似文献
13.
Iron-molybdenum cofactor synthesis in Azotobacter vinelandii Nif- mutants. 总被引:1,自引:0,他引:1
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Nif- mutants of Azotobacter vinelandii defective in dinitrogenase activity synthesized iron-molybdenum cofactor (FeMo-co) and accumulated it in two protein-bound forms: inactive dinitrogenase and a possible intermediate involved in the FeMo-co biosynthetic pathway. FeMo-co from both these proteins could activate apo-dinitrogenase from FeMo-co-deficient mutants. 相似文献
14.
Detection of human papillomavirus in cervical smears. A comparison of in situ hybridization, immunocytochemistry and cytopathology 总被引:3,自引:0,他引:3
A comparison of different methods for the detection of cervical human papillomavirus (HPV) infection was made on patients attending the cervical dysplasia clinic. Cytomorphology, immunocytochemistry and in situ hybridization were compared for their ability to detect HPV. Separate cervicovaginal smears from 50 patients were tested for HPV types 6/11, 16 and 18 by in situ hybridization using 35S-labeled DNA probes. Duplicate smears from the same patients were Papanicolaou stained and evaluated for evidence of condylomatous and dysplastic changes. Twenty-five matching cervical biopsies were immunostained for HPV capsid antigen and tested by in situ hybridization for HPV DNA. The cytologic smears of 20 patients (40%) were positive for HPV DNA. Six patients had HPV 6/11, ten had HPV 16, three had HPV 18, and one had both HPV 6/11 and HPV 16. There was a high correlation between condylomatous cytopathology and antigen and DNA detection. One-third of the specimens with condylomatous changes were DNA negative by the tested probes, suggesting the presence of other HPV types in the genital tract. 相似文献
15.
The solution conformation of model compounds for the tri'-antennary and tetraantennary (six-arm) branch point of N-linked glycans has been determined through the use of chemical shift, relaxation, and nuclear Overhauser enhancement data. The object was to establish the conformation about the glycosidic linkages in the N-linked substructure GlcNAc(beta 1,6) [GlcNAc(beta 1,2)] Man(alpha)- by estimation of values for the appropriate glycosidic torsional angles. The GlcNAc(beta 1,6) linkage in a trisaccharide model compound was found to be constrained to a narrow rotameric subpopulation about the substituted Man C5-C6 bond (omega = -60 degrees) and a narrow range of possible phi - psi values. Free rotation about the Man C5-C6 bond was obstructed by unfavorable steric interactions between the GlcNAc(beta 1,6) and GlcNAc(beta 1,2) residues. A phi, psi value of 55 degrees, 190 degrees was found to be consistent with the NMR data for the GlcNAc(beta 1,6) linkage. However, the value of psi appears to be "virtual" in that the molecule is in equilibrium between two different values (90 degrees and 252 degrees). For the GlcNAc(beta 1,2) linkage, complete agreement between all the observed NMR parameters and all the calculated ensemble average values could only be obtained with a set of potential energy functions which included hydrogen bonding. Other choices of potentials yielded calculated values that disagreed with at least two of the observed quantities. As a result, we infer that an interresidue hydrogen bond is formed, and we find it to be between the GlcNAc(beta 1,2) ring oxygen and the Man C3 hydroxyl.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
16.
David T. Osuga Milton S. Feather Mena J. Shah Robert E. Feeney 《Journal of Protein Chemistry》1989,8(4):519-528
Amino acids and peptides have been attached to the C-6 hydroxyls of the galactose and the N-acetylgalactosamine by first oxidizing the C-6 hydroxyls to the aldehydes by galactose oxidase in the presence of small amounts of catalase, followed by reductive amination (-amino group) in the presence of cyanoborohydride. The activity of oxidized antifreeze glycoprotein was >70% of the original, and considerable activity has been retained with some substitutions on reductive amination using cyanoborohydride. The following were some activities retained (as compared with the oxidized antifreeze glycoprotein): Gly, 64; (Gly)2, 88; (Gly)3, 82; (Gly)4, 70; Gly-Gly-NH2, 44, Gly-Glu, 13; Gly-Leu, 40; Gly-Tyr, 57; Gly-Gly-Leu, 50; Gly-Gly-Phe, 30; and Gly-Gly-Val, 35. On amino acid analysis of acid hydrolysates, some release of the amino acid attached by amination occurred; e.g., Gly-Tyr gave 0.26 Gly and 0.49 Tyr per disaccharide. 相似文献
17.
(R)-2-Hydroxy-1,2,4-butanetricarboxylic acid [(R)-homocitrate] has been has been recently reported to be an integral constituent of the otherwise thought to be inorganic iron-molybdenum cofactor of dinitrogenase [Hoover, T.R., Imperial, J., Ludden, P.W., & Shah, V.K. (1989) Biochemistry 28,2768-2771]. Different organic acids can substitute for homocitrate in an in vitro system for iron-molybdenum cofactor synthesis and incorporation into dinitrogenase [Hoover, T.R., Imperial, J., Ludden, P.W., & Shah, V. K. (1988) Biochemistry 27, 3647-3652]. Dinitrogenase activated with homocitrate-FeMo-co was able to reduce dinitrogen, acetylene, and protons efficiently. Homoisocitrate and isocitrate dinitrogenases did not reduce dinitrogen or acetylene, but showed very high proton reduction activities. Citrate and citramalate dinitrogenases had very low dinitrogen reduction activities and intermediate acetylene and proton reduction activities. CO inhibited proton reduction in both these cases but not in the case of dinitrogenases activated with other homocitrate analogues. By use of these and other commercially available homocitrate analogues in the in vitro system, the structural features of the homocitrate molecule absolutely required for the synthesis of a catalytically competent iron-molybdenum cofactor were determined to be the hydroxyl group, the 1- and 2-carboxyl groups, and the R configuration of the chiral center. The stringency of the structural requirements was dependent on the nitrogenase substrate used for the assay, with dinitrogen having the most stringent requirements followed by acetylene and protons. 相似文献
18.
Glucose uptake was measured in the supernatants of 18 strains ofFusobacterium species cultured in BM medium. Some species, such asF. nucleatum andF. necrophorum, used between 25% and 48% of the glucose in the medium, but the terminal pH remained near neutral. By contrast, strains ofF. mortiferum andF. necrogenes used on average over 90% of the available glucose in the medium and produced a predictably low acidic pH. Strains ofF. varium used between 86% and 91% of the glucose present but produced a near neutral pH of between 5.8 and 5.9. The metabolic fate of glucose inF. varium was, therefore, examined in more detail. Glucose stimulated the growth of this species, and [14C]glucose was incorporated into the metabolic end products and various cellular components. Protein hydrolysates, tested for their growth-promoting effects onFusobacterium species, produced two general growth response patterns. Most species grew prolifically on trypticase, proteose peptone, and yeast extract, but poorly in casamino acids and vitamin-free casamino acids. Growth in bactocasitone was poor, but for three species,F. necrophorum, F. varium, andF. nucleatum, there was an approximately linear growth response up to 0.5%. These results suggest a major role for nitrogen metabolism but do not preclude glucose as an energy source in at least some species ofFusobacterium. 相似文献
19.
20.
Characteristics of glutamate dehydrogenase, a new diagnostic marker for the genus Fusobacterium 总被引:3,自引:0,他引:3
Enzymes representative of carbohydrate and nitrogen metabolism were screened for their presence and activity amongst species of the genus Fusobacterium. Glutamate dehydrogenase (GDH) was reliably detected in all 25 strains studied. The pH profile of this enzyme and the DNA base composition of selected strains were also determined. DNA base composition of selected strains ranged between 28-32.9 mol% G + C. GDH was active between pH 7.5-11.5 but two pH profiles of activity, with optima at 9.5 and 10.5, were discernible among species. Apart from Fusobacterium nucleatum, which had a heterogeneous enzyme pattern, the GDH electrophoretic mobility was constant within a species but in a few cases the enzyme bands overlapped. A combination of the pH profile, the GDH electrophoretic pattern and the DNA base composition provided clear separation of the test organisms into discrete groups; however, a larger number of strains must be examined before the full potential of these tests can be evaluated. 相似文献