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61.
62.
P J Martin J A Ledbetter E A Clark P G Beatty J A Hansen 《Journal of immunology (Baltimore, Md. : 1950)》1984,132(2):759-765
The complexity of the suppressor/cytotoxic subset marker of human T lymphocytes was demonstrated by biochemical analysis, cross-blocking experiments, phylogenetic comparisons, and functional studies. At the biochemical level, the antigen was shown to be a heteromultimer of at least three polypeptide chains covalently associated into four different higher m.w. species. Sixteen different murine monoclonal antibodies were used to map epitopes of this heteromultimeric complex. Cross-blocking experiments undertaken with six directly labeled reference antibodies identified at least seven spacially distinct epitopes. Flow microfluorometric analysis of peripheral blood lymphocytes showed two distinct subpopulations of bright and dull-stained cells that differed approximately 10-fold in antigen density. The distribution of epitopes on bright and dull cells was not uniform because in several combinations, blocking was observed on bright cells only. Studies with nonhuman primate T cells demonstrated a high degree of phylogenetic heterogeneity in the antigen. The combined cross-blocking and primate data divided the 17 antibodies into 15 groups. Each of the antibodies was capable of blocking lysis by alloreactive cytotoxic T lymphocytes, indicating that the mechanism of inhibition may not necessarily involve hindrance of an active site. 相似文献
63.
Medium-chain fatty acid synthesis 总被引:1,自引:0,他引:1
64.
Interspecies hydrogen transfer in co-cultures of methanol-utilizing acidogens and sulfate-reducing or methanogenic bacteria 总被引:2,自引:0,他引:2
Abstract The metabolism of methanol by acidogenic bacteria ( Butyribacterium methylotrophicum, Sporomusa ovata and Acetobacterium woodii ) was studied in pure culture and in defined mixed cultures with sulfate-reducing bacteria ( Desulfovibrio vulgaris ) or methanogenic bacteria ( Methanobrevibacter arboriphilus strain AZ). In the mixed cultures, less acids (acetate and/or butyrate) were formed per unit methanol converted than in pure cultures. In these mixed cultures, a significant production of sulfide or methane was observed despite the inability of the sulfate reducer and the methanogen to use methanol as an energy substrate. These results are explained in terms of interspecies hydrogen transfer between the acidogens (converting part of the methanol to 1 CO2 and 3 H2 ) and the Desulfovibrio or Methanobrevibacter species. The bioenergetic aspects of this process and its ecological implications are discussed. 相似文献
65.
Formation of (4R)- and (4S)-4-hydroxyochratoxin A and 10-hydroxyochratoxin A from Ochratoxin A by rabbit liver microsomes. 总被引:3,自引:3,他引:0 下载免费PDF全文
Three metabolites were formed from ochratoxin A in the presence of rabbit liver microsomal fractions and NADPH. They were isolated by extraction, thin-layer chromatography, and high-pressure liquid chromatography. Two of them were identified as (4R)- and (4S)-4-hydroxyochratoxin A. It is suggested on the basis of mass and nuclear magnetic resonance spectroscopy that the third metabolite is 10-hydroxyochratoxin A. The formation of the metabolites was inhibited by carbon monoxide and metyrapone and was stimulated when microsomes from phenobarbital-treated animals were used. The results suggest that cytochrome P-450 catalyzes the formation of these metabolites. 相似文献
66.
67.
Abortive Infection of F-Plasmid-Containing Escherichia coli Cells by Bacterial Virus T7 Is Determined by the Right End of T7 Gene 1 总被引:1,自引:0,他引:1 下载免费PDF全文
Phage T7 infects male (F-plasmid-carrying) Escherichia coli cells abortively, whereas the closely related phage T3 grows normally. The inability or ability of phage to replicate in male host cells depends on whether the right end of gene 1 (coding for the phage-specific RNA polymerase) consists of T7 or T3 DNA base sequences. 相似文献
68.
Summary Reaction kinetic analysis of the electrical properties of the electrogenic Cl– pump inAcetabularia has been extended from steady-state to nonsteady-state conditions: electrical frequency responses of theAcetabularia membrane have been measured over the range from 1 Hz to 10 kHz at transmembrane potential differences across the plasmalemma (V
m
) between –70 and –240 mV using voltage-clamp techniques. The results are well described by an electrical equivalent circuit with three parallel limbs: a conventional membrane capacitancec
m
, a steadystate conductanceg
o
(predominantly of the pump pathway plus a minor passive ion conductance) and a conductanceg
s
in series with a capacitancec
p
which are peculiar to the temporal behavior of the pump. The absolute values and voltage sensitivities of these four elements have been determined:c
m
of about 8 mF m–2 turned out to be voltage insensitive; it is considered to be normal.g
o
is voltage sensitive and displays a peak of about 80 S m–2 around –180 mV. Voltage sensitivity ofg
s
could not be documented due to large scatter ofg
s
(around 80 S m–2).c
p
behaved voltage sensitive with a notch of about 20 mF m–2 around –180 mV, a peak of about 40 mF m–2 at –120 mV and vanishing at –70 mV. When these data are compared with the predictions of nonsteady-state electrical properties of charge transport systems (U.-P. Hansen, J. Tittor, D. Gradmann, 1983,J. Membrane Biol. in press), model A (redistribution of states within the reaction cycle) consistently provides magnitude and voltage sensitivity of the elementsg
o
,g
s
andc
p
of the equivalent circuit, when known kinetic parameters of the pump are used for the calculations. This analysis results in a density of pump elements in theAcetabularia plasmalemma of about 50 nmol m–2. The dominating rate constants for the redistribution of the individual states of the pump in the electric field turn out to be in the range of 500 sec–1, under normal conditions. 相似文献
69.
Alloantigen-specific cytotoxic and suppressor T lymphocytes are derived from phenotypically distinct precursors 总被引:19,自引:0,他引:19
N K Damle N Mohagheghpour J A Hansen E G Engleman 《Journal of immunology (Baltimore, Md. : 1950)》1983,131(5):2296-2300
Although Leu-2+ (OKT8+) T cells activated in the mixed lymphocyte reaction (MLR) mediate both alloantigen-specific cytotoxicity and suppression of alloantigen-induced proliferation, it is not known whether these functions derive from a single cell type or phenotypically distinct cells. This study was undertaken to examine the alloantigen-specific cytolytic and suppressor potential of two subpopulations of Leu-2+ cells distinguishable from one another on the basis of their binding to the monoclonal antibody 9.3. Leu-2+, 9.3+ and Leu-2+, 9.3- populations were purified from peripheral blood, cultured for 7 days with autologous helper/inducer (Leu-3+) cells and allogeneic non-T cells, and reisolated before testing for cytotoxicity and suppression. All detectable alloantigen-specific cytolytic activity was confined to the Leu-2+, 9.3+ subpopulation. Killing by this subset was specific for the HLA-A and B (class I) major histocompatibility complex (MHC) antigens of the priming cell. By contrast, suppression of proliferation was mediated predominantly by the Leu-2+, 9.3- cells, and suppression by this subpopulation was specific for the HLA-DR (class II) MHC antigens of the priming cell. The development of suppression by Leu-2+, 9.3- cells was unaffected by cyclosporin A (CsA), an agent shown previously to block the development of cytolytic but not suppressor cells in MLR. Alloactivated Leu-2+, 9.3+ cells were slightly inhibitory of fresh MLR, but this effect as well as the development of cytolytic cells was completely abrogated by CsA. These results indicate that suppressor and cytolytic Leu-2+ T cells activated in MLR are derived from distinct precursors separable by antibody 9.3. 相似文献
70.
Evolution of epitopes on human and nonhuman primate lymphocyte cell surface antigens 总被引:4,自引:0,他引:4
Edward A. Clark Paul J. Martin John A. Hansen Jeffrey A. Ledbetter 《Immunogenetics》1983,18(6):599-615
The T- and B-cell surface polypeptides detected by an international workshop panel of 100 mouse monoclonal antibodies (M.Ab) were biochemically defined by radioimmunoprecipitation. Eight T-cell-associated molecules and eight B-cell-associated molecules were identified by multiple antibodies in the panel. Clusters of antibodies specific for the same polypeptide were then compared for their reactivity against peripheral blood mononuclear cells (PBMC) from 11 nonhuman primate species. All the major T- and B-cell antigens present in humans were also expressed in some nonhuman primates. M.Ab to the same antigen were found to react with distinct epitope groups that differed in their phylogenetic distribution. Some epitopes were highly conserved, while other epitopes on the same molecule were only expressed in hominoids and were not detected in old world and new world monkeys. Our detailed analysis of the phylogeny of 37 T-cell antigen epitopes on ten different molecules revealed there was no clear correspondence between the number of epitopes shared and evolutionary distance. Rather the data suggest that parallelism with back mutation may be a common mechanism in the evolution of T-cell antigens. The data also show that the tissue distribution of T-cell antigens can differ between primate species; for example, M.Ab to human Tp45 Tla-Qa-like antigens that did not react with human PBMC did react with PBMC from new world monkeys. 相似文献