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951.
David O. Lambeth Gwen R. Ericson Mark A. Yorek Paul D. Ray 《Biochimica et Biophysica Acta (BBA)/General Subjects》1982,719(3):501-508
The influences of buffers and iron chelators on the rate of autoxidation of Fe2+ were examined in the pH range 6.0–7.4. The catalysis by Fe2+ and Fe3+ of the autoxidation of dithiothreitol was also investigated. In buffers which are non- or poor chelators of iron, 0.25 mM Fe2+, and 0.3 mM dithiothreitol when present with iron, oxidize within minutes at pH 7.4 and 30°C. The stability of each increases as the pH is decreased and more than 90% of each remains after 1 h at pH 6.0. In the presence of buffers or oxy-ligands which preferentially and strongly chelate Fe3+ over Fe2+, Fe2+ autoxidizes rapidly in the pH range 6.0–7.4 while dithiothreitol is protected. Ligands which preferentially bind strongly to Fe2+ stabilize both Fe2+ and dithiothreitol at pH 7.4. Dithiothreitol readily reduces Fe3+ in non-chelating buffers or in the presence of strong chelators of Fe2+, however, the ferrous ions produced are prone to reoxidation at higher pH values. These results show that Fe2+ and dithiothreitol are very susceptible to autoxidation in the neutral pH range, and that the rates are strongly influenced by the presence of chelators of Fe2+ and Fe3+. The rapid autoxidations of these species need to be taken into account when designing and interpreting experiments involving Fe2+ or both dithiothreitol and iron. 相似文献
952.
Levels of ammonia-assimilating enzymes (glutamate dehydrogenase, glutamine synthetase, glutamate synthase) were determined in extracts of Sporotrichum pulverulentum grown under different conditions with respect to both nitrogen source and concentration. Evolution of 14CO2 from 14C-synthetic lignin by fungal cultures grown under parallel conditions was also determined as a measure of lignin decomposition and the suppressive effect of nitrogen on ligninolysis confirmed. Under low nitrogen conditions, fungal extracts exhibited relatively high levels of NADP-dependent glutamate dehydrogenase and glutamine synthetase dehydrogenase. Conversely, in high nitrogen extracts, lower levels of NADP-dependent glutamate dehydrogenase and glutamine synthetase activity, and higher levels of NAD-dependent glutamate dehydrogenase, were recorded. Possible effects of enzyme activities on intracellular pool concentrations of glutamate/glutamine, and the implications for the regulation of lignin metabolism, are discussed.A preliminary report was presented at The Ekman Days 1981, International Symposium on Wood and Pulping Chemistry, Stockholm, Sweden, June 9–12, 1981. 相似文献
953.
Timothy J. Eberlein Maury Rosenstein Paul Spiess Robert Wesley Steven A. Rosenberg 《Cancer immunology, immunotherapy : CII》1982,13(1):5-13
Summary Recently techniques have been developed for the long-term growth of cytotoxic T-lymphoid cells in vitro with T cell growth factor (TCGF). We have investigated the use of these in vitro-expanded T cells for the immunotherapy of a disseminated syngeneic murine FBL-3 lymphoma. In this model, mice with disseminated tumor were treated on day 5 with 180 mg cytoxan/kg and then 5 h later were given lymphoid cells IP. In vivo-immunized lymphocytes resulted in significantly improved survival in three of three experiments, curing 52% of 38 animals, compared with treatment with cytoxan alone (0 of 31 cured) or cytoxan plus unimmunized cells (0 of 40 cured) (P<0.0005). In vivo-immunized lymphocytes were re-exposed to FBL-3 tumor in vitro for 5 days in complete medium (CM) or lectin-free TCGF (LF-TCGF). Both groups showed significantly improved survival in six of six experiments. Cytoxan cured 17% of 66 animals, while cytoxan plus normal lymphocytes after IVS cured 6% of 47 animals. In vivo-immunized cells resensitized in vitro to FBL-3 in CM or LF-TCGF cured 82% of 50 animals (P<0.001) and 72% of 61 animals (P<0.001), respectively. Cells from in vivo- and in vitro-sensitized lymphocytes exhibited no cytotoxicity in our in vitro 51Cr-release assay; expansion of these cells resulted in significant specific lysis of fresh FBL-3 targets. Adoptive transfer of immune lymphocytes resensitized to FBL-3 tumor in vitro and expanded in LF-TCGF conferred a significant survival benefit (P<0.001, curing 7 of 27 animals) compared with all controls. These expanded cells were then continuously grown in LF-TCGF for 2 1/2 months. Again, in vivo-immunized lymphocytes resensitized to FBL-3 tumor and expanded in LF-TCGF for 2 1/2 months cured 56% of the animals with disseminated tumor, significantly prolonging survival over that recorded in any control group (P<0.0002). Irradiation of these same cells totally abolished their efficacy. Clones were generated from IVS and continuously grown in LF-TCGF. Two of these clones were very cytotoxic for fresh FBL-3 (>4,000 lytic units/106 cells). When adoptively transferred to mice in this chemoimmunotherapy model these cytotoxic clones significantly enhanced survival over that recorded following treatment with cytoxan alone (P<0.00001), though prolongation of survival was small. Implications of these results for application of these techniques to other less antigenic tumors and human cancers are discussed. 相似文献
954.
Genetic homology and crossing over in the X and Y chromosomes of mammals 总被引:51,自引:4,他引:47
Paul S. Burgoyne 《Human genetics》1982,61(2):85-90
Summary The X-Y crossover model described in this paper postulates that (1) the pairing observed between the X and the Y chromosome at zygotene is a consequence of genetic homology, (2) there is a single obligatory crossover between the X and Y pairing segments, and (3) the segment of the X which pairs with the Y is protected from subsequent X inactivation. Genes distal to the proposed crossover (pseudoautosomal genes) will appear to be autosomally inherited because they will be transmitted to both male and female offspring. Some criteria for identifying pseudoautosomal genes are outlined.The existence of a single obligatory crossover between the X and Y of the mouse is strongly supported by a recent demonstration that the sex-reversing mutation Sxr, which is passed equally to XX and XY offspring by male carriers, is transmitted on the sex chromosomes. Pseudoautosomally inherited genes may also be responsible for XX sex reversal in goats and familial XX sex reversal in man. 相似文献
955.
956.
Pseudomonas aeruginosa strain PAO formed a mannitol-binding protein that was coinducible with mannitol uptake activity. One species of mannitol-binding protein was isolated from disrupted cell suspensions and the protein also was released from mannitol-grown cells by osmotic shock treatment. The mannitol-binding protein )molecular weight 37,000) was purified 49-fold and resolved from the enzyme mannitol dehydrogenase (molecular weight 85,000), which did not exhibit mannitol-binding activity. Mannitol-binding protein had an isoelectric point (pI) of 8.3 and an apparent dissociation constant (K
D
) of 2.3 M for mannitol. Mannitol binding was unaffected by glucose and glycerol in competitive inhibition studies, although mannose, fructose, and sorbitol caused 5 to 20% inhibition of binding at concentrations equimolar with mannitol. 相似文献
957.
Carl R. Woese Paul Blanz Robert B. Hespell Christine M. Hahn 《Current microbiology》1982,7(2):119-124
Helical bacteria from the generaSpirillum, Oceanospirillum, Aquaspirillum, andAzospirillum—as well asSerpens flexibilis—were characterized by oligonucleotide cataloging of 16S rRNA in order to establish their phylogenetic relationships to one another and to Gramnegative bacteria in general. The various genera of helical bacteria are not specifically related to one another (to the exclusion of nonhelical bacteria) and, where tested, the individual genera as presently constituted are not phylogenetically coherent (with the possible exception ofOceanospirillum, which may form a deep grouping). 相似文献
958.
Synopsis The most important factor affecting the potential range of 14 non-native fishes in Florida appears to be their lack of tolerance to low temperatures. In this study, temperatures associated with reduction in feeding, cessation of feeding, loss of equilibrium and death were identified by decreasing water temperature 1°C day–1. Fishes tested and their mean lower lethal temperatures were: Astronotus ocellatus (12.9°C), Belonesox belizanus (9.7°C), Cichlasoma bimaculatum (8.9°C), C. cyanoguttatum (5.0°C), C. meeki (10.3°C), C. octofasciatum (8.0°C), C. trimaculatum (10.9°C), Clarias batrachus (9.8°C), Hemichromis bimaculatus (9.5°C), Hypostomus sp. (11.2°C), Tilapia aurea (6.2°C), T. mariae (11.2°C), T. melanotheron (10.3°C) and T. mossambica (9.5°C). These data indicate that temperature is less limiting for these fishes in Florida than was previously recognized.Contribution Number 18, Non-Native Fish Research Laboratory, Florida Game and Fresh Water Fish Commmission, 801 N. W. 40th Street, Boca Raton, FL 33431, U.S.A. 相似文献
959.
A quantitative autoradiographic method for the measurement of local rates of brain protein synthesis
We have developed a new method for measuring local rates of brain protein synthesis in vivo. It combines the intraperitoneal injection of a large dose of low specific activity amino acid with quantitative autoradiography. This method has several advantages: 1) It is ideally suited for young or small animals or where immobilizing an animal is undesirable. 2) The amino acid injection floods amino acid pools so that errors in estimating precursor specific activity, which is especially important in pathological conditions, are minimized. 3) The method provides for the use of a radioautographic internal standard in which valine incorporation is measured directly. Internal standards from experimental animals correct for tissue protein content and self-absorption of radiation in tissue sections which could vary under experimental conditions.A preliminary report of this work was presented at the 11th annual meeting of the Society for Neuroscience, Los Angeles, California, October 18–23, 1981. 相似文献
960.
Leon Milewich Terry S. Hendricks Bettie Sue Masters Rene A. Frenkel Paul C. Mac Donald 《Archives of biochemistry and biophysics》1981,211(2):530-536
The estrogen synthetase present in human placental microsomes appears to be dependent on the cooperative interaction of the reduced cofactors NADPH and NADH for optimal activity. Using steady-state concentrations of either cofactor, it was found that while the estrogen synthetase activity followed hyperbolic saturation kinetics with NADPH (Kmapp = 14 μM), the enzyme followed sigmoidal saturation kinetics when the cofactor was NADH, with the half-maximum velocity attained at a cofactor concentration of 1.1 mm. The maximum velocity obtained with NADPH as the cofactor was greater than with corresponding concentrations of NADH. Estrogen synthetase activity in the presence of NADH was not due to NADPH contamination. NADH, in the presence of small concentrations of NADPH (0.5 to 5 μm), stimulated significantly the rate of estrogen formation from androstenedione by placental microsomes and, in addition, the enzyme saturation kinetics changed from sigmoidal to hyperbolic, thus mimicking the effect of NADPH. Estrogen synthetase activity, measured in the presence of 1 mm NADH, was stimulated in a dose-dependent manner by NADPH (Kmapp = 0.4 μM NADPH) and, when the enzyme was measured in the presence of 5 μm NADPH, the activity was stimulated in a dose-dependent manner by NADH (Kmapp = 45 μM NADH). Estrogen synthetase activity measured in the presence of NADH, without and with NADPH (1 μm) remained linear both with time of incubation for approximately 15 min and with microsomal protein concentration up to 3 mg/ml. The apparent Km of estrogen synthetase for androstenedione, when measured in the presence of NADH, was 1 μm. The synergistic interaction between NADH and NADPH in stimulating placental estrogen synthetase activity observed in vitro may, conceivably, take place in vivo in the intact placenta. 相似文献