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41.
Simon C. Andrews Madeleine C. Brady Amyra Treffry John M. Williams Stephen Manna Maud I. Cleton Wim de Bruijn Pauline M. Harrison 《Biometals》1988,1(1):33-42
Summary Haemosiderin has been isolated from siderosomes and ferritin from the cytosol of livers of rats iron-loaded by intraperitoneal injections of iron-dextran. Siderosomal haermosiderin, like ferritin, was shown by electron diffraction to contain iron mainly in the form of small particles of ferrihydrite (5Fe2O3 · 9H2O), with average particle diameter of 5.36±1.31 nm (SD), less than that of ferritin iron-cores (6.14±1.18 nm). Mössbauer spectra of both iron-storage complexes are also similar, except that the blocking temperature,T
B, for haemosiderin (23 K) is lower than that of ferritin (35 K). These values are consistent with their differences in particle volumes assuming identical magnetic anisotropy constants. Measurements of P/Fe ratios by electron probe microanalysis showed the presence of phosphorus in rat liver haemosiderin, but much of it was lost on extensive dialysis. The presence of peptides reacting with anti-ferritin antisera and the similarities in the structures of their iron components are consistent with the view that rat liver haemosiderin arises by degradation of ferritin polypeptides, but its peptide pattern is different from that found in human-thalassaemia haemosiderin. The blocking temperature, 35 K, for rat liver ferritin is near to that reported, 40 K, for human-thalassaemia spleen ferritin. However, the haemosiderin isolated from this tissue, in contrast to that from rat liver, had aT
B higher than that of ferritin. The iron availability of haemosiderins from rat liver and human-thalassaemic spleen to a hydroxypyridinone chelator also differed. That from rat liver was equal to or greater, and that from human spleen was markedly less, than the iron availability from either of the associated ferritins, which were equivalent. The differences in properties of the two types of haemosiderin may reflect their origins from primary or secondary iron overload and differences in the duration of the overload. 相似文献
42.
Flow cytometry and cell sorting techniques have been used together with repeated measurement in an attempt to define better the radiation survival response of asynchronously dividing Chinese hamster V79-171 cells under aerobic and hypoxic conditions. Although the first two decades of cell inactivation have been examined, particular attention has been given to the low-dose range of a few grays, as used in individual radiation therapy treatments. A single linear-quadratic dose-response function was consistently unable to fit both the low-dose and high-dose data satisfactorily, suggesting a two-component response. Separate fitting of the low-dose and high-dose portions of the response yielded alpha and beta values which differed significantly (P = 0.001 to 0.002). The data are consistent with the hypothesis that the observed substructure simply reflects the presence of subpopulations of sensitive (G1-, G2-phase) and resistant (late S-phase) cells, which are resolved in these measurements. These results may have significance for certain situations in radiation therapy and in biophysical modeling of the radiation response. 相似文献
43.
M P Czech B M Clancy A Pessino C W Woon S A Harrison 《Trends in biochemical sciences》1992,17(5):197-201
Facilitated sugar entry into mammalian cells is catalysed by multiple isoforms of the glucose transporter and regulated by hormonal stimuli, nutritional status and oncogenesis. A large reserve of latent glucose transport capacity must be maintained by muscle and adipose cells that are sensitive to insulin, the primary activator of sugar uptake after feeding. Intracellular sequestration of sugar transporters accounts for a large part of this latent capacity, but new findings suggest that there is also reversible suppression of intrinsic catalytic activity of those glucose transporters residing at the cell surface. The mechanism of this suppression appears to be occlusion or disruption of the exofacial sugar-binding sites on the glucose-transporter proteins. 相似文献
44.
Immunocytochemical localization of glucocorticoid receptors in cells, cytoplasts, and nucleoplasts 总被引:2,自引:0,他引:2
A monoclonal antibody has been used to assess the intracellular localization of the glucocorticoid receptor in rodent L-929 fibroblasts and GH3 pituitary tumor cells. Whole cells from both cell lines showed immunoreactivity in the cytoplasm and nucleus. However, when cytoplasts and nucleoplasts of these cells were examined, only L-cells showed strong antibody binding in both fractions; in contrast, GH3 cells exhibited nuclear staining and slight cytoplasmic staining. These results are discussed in terms of the current findings regarding the intracellular location of steroid hormone receptors. 相似文献
45.
Esterification by rat liver microsomes of retinol bound to cellular retinol-binding protein 总被引:1,自引:0,他引:1
We have investigated the esterification by liver membranes of retinol bound to cellular retinol-binding protein (CRBP). When CRBP carrying [3H]retinol as its ligand was purified from rat liver cytosol and incubated with rat liver microsomes, a significant fraction of the [3H]retinol was converted to [3H]retinyl ester. Esterification of the CRBP-bound [3H]retinol, which was maximal at pH 6-7, did not require the addition of an exogenous fatty acyl group. Indeed, when additional palmitoyl-CoA or coenzyme A was provided, the rate of esterification increased either very slightly or not at all. The esterification reaction had a Km for [3H]retinol-CRBP of 4 +/- 0.6 microM and a maximum velocity of 145 +/- 52 pmol/min/mg of microsomal protein (n = 4). The major products were retinyl palmitate/oleate and retinyl stearate in a ratio of approximately 2 to 1 over a range of [3H]retinol-CRBP concentrations from 1 to 8 microM. The addition of progesterone, a known inhibitor of the acyl-CoA:retinol acyltransferase reaction, consistently increased the rate of retinyl ester formation when [3H]retinol was delivered bound to CRBP. These experiments indicate that retinol presented to liver microsomal membranes by CRBP can be converted to retinyl ester and that this process, in contrast to the esterification of dispersed retinol, is independent of the addition of an activated fatty acid and produces a pattern of retinyl ester species similar to that observed in intact liver. A possible role of phospholipids as endogenous acyl donors in the esterification of retinol bound to CRBP is supported by our observations that depletion of microsomal phospholipid with phospholipase A2 prior to addition of retinol-CRBP decreased the retinol-esterifying activity almost 50%. Conversely, incubating microsomes with a lipid-generating system containing choline, CDP-choline, glycerol 3-phosphate, and an acyl-CoA-generating system prior to addition of retinol-CRBP increased retinol esterification significantly as compared to buffer-treated controls. 相似文献
46.
T Harrison 《American journal of physical anthropology》1986,71(3):265-284
Recent paleontological collections at the middle Miocene locality of Maboko Island in Kenya, dated at 15-16 million years, have yielded numerous new specimens belonging to at least five species of fossil anthropoids. The most common species of ape at the site, a medium-sized primate with a very distinctive dental morphology, clearly represents a previously undescribed taxon. When compared with other Miocene anthropoids from East Africa, it has its closest affinities with the poorly known species Rangwapithecus vancouveringi from the early Miocene locality of Rusinga Island. The species from Maboko Island is described here as belonging to a new genus of fossil anthropoid, to which "Rangwapithecus" vancouveringi is also referred. The new genus has a highly distinctive suite of derived characters of its molars and premolars, which it shares with Oreopithecus bambolii from the late Miocene of Europe. These synapomorphies indicate a close phyletic relationship between the East African species and Oreopithecus and form the basis for the inclusion of these taxa in a single family, the Oreopithecidae Schwalbe, 1915. In many respects, however, the East African forms are more conservative than Oreopithecus, and in a general sense they can be regarded as an intermediate grade between Oreopithecus and the more generalized early Miocene catarrhines, the proconsuloids. There is, therefore, good fossil evidence to indicate that the origins of the Oreopithecidae can be traced back to the early Miocene of Africa. 相似文献
47.
Structure of turnip crinkle virus. III. Identification of a unique coat protein dimer 总被引:1,自引:0,他引:1
P G Stockley A L Kirsh E P Chow J E Smart S C Harrison 《Journal of molecular biology》1986,191(4):721-725
The minor structural protein (p80), found in about one copy per virion in turnip crinkle virus (TCV), is shown by amino acid analysis and peptide mapping to be a covalent dimer of the major coat protein (p40). The covalent linkage occurs near the N termini of the crosslinked chains. These data suggest that TGV and related viruses contain 178 copies of p40 (89 non-covalent dimers) and one copy of p80 (covalent dimer of two additional p40 chains). The presence of p80 in the salt-stable RNA-protein complex formed when TCV dissociates, as described in an accompanying paper, indicates that the covalent modification affects binding to RNA. We suggest that p80 might be the final dimer to be incorporated into the shell and that it might also be the site for initiation of uncoating. 相似文献
48.
When grown in the presence of serum with added insulin, Chinese hamster embryonic fibroblasts (CHEF/18) cells can be induced to become preadipocytes that are committed to the adipocyte pathway of terminal differentiation (Sager, R., and P. Kovac, 1982, Proc. Natl. Acad. Sci. USA, 79:480-484). We found that commitment to the adipocyte pathway, as well as terminal differentiation to form mature adipocytes, can occur in a defined serum-free medium containing insulin. When CHEF/18 cells are plated in serum-containing medium, only 5-10% of cells in each colony undergo terminal differentiation, whereas in serum-free medium, greater than 90% of the cells became adipocytes. These and other results show that CHEF/18 cells require no adipogenic factors in addition to insulin and the other components of the serum-free medium (transferrin, epithelial growth factor, thrombin) to form adipocytes, and furthermore, that serum inhibits the rate of terminal adipocyte differentiation of these cells. As little as 10 ng/ml insulin added to serum-containing medium can induce adipogenesis, suggesting that insulin rather than an insulinlike growth factor is the active agent. The results further demonstrate that virtually every CHEF/18 cell can be induced into the adipocyte pathway. 相似文献
49.
Summary A lectin, which may be involved in cell to cell adhesion during erythropoiesis in rabbit bone marrow, has been isolated and characterized. Several electron microscopical techniques have been used to investigate the cell surface distribution of this lectin in bone marrow utilizing colloidal gold conjugates of anti-lectin IgG or protein A. The lectin is present at the surface of erythroid cells at all stages of development but no lectin was detected on the surface of myeloid cells. The limitations and complementary nature of the techniques used are discussed. 相似文献
50.
The human placenta contains two distinct binding and immunoreactive species of insulin-like growth factor-I receptors 总被引:6,自引:0,他引:6
Two species of insulin-like growth factor-I (IGF-I) receptors in human placenta have been delineated on the basis of their immunoreactivity with an autoantiserum (B-2) to the insulin receptor. When all the IGF-I binding sites in solubilized human placenta were assayed by polyethylene glycol precipitation, a curvilinear Scatchard plot was obtained which could be resolved into two single classes of binding sites: one immunoprecipitable by B-2 IgG and the other, nonimmunoprecipitable. The B-2 reactive sites bound IGF-I with lower affinity (Kd = 7.1 X 10(-10) M) than the B-2 nonreactive sites (Kd = 2.1 X 10(-10) M) and cross-reacted more readily with insulin, the IGF-I/insulin-binding potencies being congruent to 120 and congruent to 1100, respectively. Both receptor subtypes bound IGF-I with congruent to 30-fold higher affinity than multiplication-stimulating activity, and, after affinity cross-linking with 125I-IGF-I, migrated as specific reduced bands of Mr = 138,000 during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The subunit sizes of the B-2 reactive IGF-I receptor were similar to those of the insulin receptor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 125I-labeled receptors immunoprecipitated by autoantiserum B-2 or autoantiserum B-10 (which recognizes only insulin receptors) revealed, in both cases, specific reduced bands of Mr = 130,000 and 90,000; the same bands were also seen after sequential precipitation with B-10 and B-2 antisera to enrich the proportion of IGF-I receptors recovered. The presence of two distinct binding and immunoreactive species of IGF-I receptors in human placenta raises the possibility that cell- or tissue-specific isotypes of the IGF-I receptor could mediate the different biological actions of IGF-I. 相似文献