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排序方式: 共有190条查询结果,搜索用时 15 毫秒
1.
Nonadditive interactive effects of polychlorinated biphenyl congeners in rats: role of the 2,3,7,8-tetrachlorodibenzo-p-dioxin receptor 总被引:1,自引:0,他引:1
B Leece M A Denomme R Towner A Li J Landers S Safe 《Canadian journal of physiology and pharmacology》1987,65(9):1908-1912
Administration of 3,3',4,4',5,5'-hexa-,3,3',4,4',5-penta-, and 2,3,3'4,4'5-hexa-chlorobiphenyl to immature male Wistar rats caused a thymic atrophy at high dose levels (1.25, 1.0, and 100 mumol/kg, respectively) and induced the hepatic cytochrome P-448 dependent monooxygenases (benzo[a]pyrene hydroxylase and ethoxyresorufin O-deethylase) at both high and low (0.25, 0.01, and 5 mumol/kg, respectively) doses. In contrast, 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP) (300 mumol/kg) did not elicit any of these effects but elevated hepatic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) cytosolic receptor protein levels (threefold) as previously reported. The effects of hepatic receptor modulation by 2,2',4,4',5,5'-HCBP (300 mumol/kg) on the enzyme induction activities of 3,3'4,4',5-penta-, 3,3'4,4',5,5'-hexa-, and 2,3,3',4,4',5-hexa-chlorobiphenyl were dose-dependent; no interactive effects were observed at high (toxic) doses of these compounds, whereas apparent synergistically increased hepatic microsomal monooxygenase induction activities were noted at the lower submaximal induction doses. It was concluded that the increased responsiveness of the rats was due to elevated hepatic 2,3,7,8-TCDD receptor levels. 相似文献
2.
Foodstuffs were artificially contaminated with Escherichia coli carrying plasmid pBR322, dot blotted onto nylon membranes and briefly subjected to microwaves in the presence of 1·5 mol/l NaC1/0·5 mol/l NaOH. Subsequent hybridization with a biotin-labelled probe specific for pBR322 enabled the detection of cell concentrations > 104 cells/dot blot, equivalent to 2 × 107 cells/g food tested. This shortened and simplified method was effective for all ten foods tested, generated low background levels and should be applicable to a wide range of bacteria. 相似文献
3.
Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes 总被引:8,自引:0,他引:8
Delarbre C; Kashi Y; Boursot P; Beckmann JS; Kourilsky P; Bonhomme F; Gachelin G 《Molecular biology and evolution》1988,5(2):120-133
We have examined the phylogenetic distribution of two t-specific markers
among representatives of various taxa belonging to the genus Mus. The
centromeric TCP-1a marker (a testicular protein variant specific for all
t-haplotypes so far studied) has also been apparently detected in several
non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor
species. By contrast, a t-specific restriction- fragment-length
polymorphism allele (RFLP) of the telomeric alpha- globin pseudogene DNA
marker alpha-psi-4 was found only in animals belonging to the M.
musculus-complex species either bearing genuine t- haplotypes or, like the
M. m. bactrianus specimen studied here, likely to do so. This t-specific
alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles
of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or
M. spretus ones. These results suggest the presence of t-haplotypes and of
t-specific markers in populations other than those belonging to the M. m.
domesticus and M. m. musculus subspecies, implying a possible origin for
t-haplotypes prior to the radiation of the most recent offshoot of the Mus
genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.
相似文献
4.
At least one plasmid from each of the incompatibility groups B, C, FIV, H2/S, I alpha, I delta, P, W and X was shown to be capable of transfer from Escherichia coli K12 to Acinetobacter calcoaceticus EBF65/65. Transfer was influenced by the presence of pAV2 (thought to encode a restriction-modification system) in the recipient strain; however, not all plasmids belonging to a particular incompatibility group behaved identically. All plasmids were unstable to varying degrees in A. calcoaceticus EBF65/65, but under suitable conditions were capable of transfer to further strains of EBF65/65 and re-transfer to E. coli K12. Of 40 recently isolated trimethoprim R plasmids 31 transferred successfully from E. coli K12 to A. calcoaceticus EBF65/65, but 17 of these 31 required the introduction of a second mobilizing plasmid for re-transfer to occur. 相似文献
5.
Acid -glucosidase in amniotic fluid 总被引:2,自引:0,他引:2
A L Fluharty M L Scott M T Porter H Kihara M G Wilson J W Towner 《Biochemical medicine》1973,7(1):39-51
6.
Replication-competent picornaviruses with complete genomic RNA 3' noncoding region deletions. 总被引:1,自引:0,他引:1
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The genomic RNA 3' noncoding region is believed to be a major cis-acting molecular genetic determinant for regulating picornavirus negative-strand RNA synthesis by promoting replication complex recognition. We report the replication of two picornavirus RNAs harboring complete deletions of the genomic RNA 3' noncoding regions. Our results suggest that while specific 3'-terminal RNA sequences and/or secondary structures may have evolved to promote or regulate negative-strand RNA synthesis, the basic mechanism of replication initiation is not strictly template specific and may rely primarily upon the proximity of newly translated viral replication proteins to the 3' terminus of template RNAs within tight membranous replication complexes. 相似文献
7.
The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum 总被引:29,自引:22,他引:7
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Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature. 相似文献
8.
Summary A 1730-g male infant, born at 37 weeks gestation, had multiple congenital anomalies, consisting of microcephaly, hypertelorism, bilateral cleft lip and palate, micrognathia, lowset ears, and cryptorchidism. Chromosome analysis showed a recombinant 22 derived from the paternal inversion (22) (p13q12.2). The proband's karyotype is 46,XY,rec(22),dup q,inv(22)(p13q12.2)pat, which has a duplication of q12.2qter. An identical recombinant has been reported in a female infant in Mexico whose mother was a carrier of the inversion. Similar congenital anomalies present in these two patients demonstrate the phenotype of duplication of the distal long arm 22. This report also documents the occurrence of an identical inversion in two apparently unrelated Mexican families. 相似文献
9.
Transposon Tn916 was shown to be capable of direct conjugative transfer in broth and membrane matings between strains of Escherichia coli K12 and between E. coli K12 and Haemophilus influenzae type b. Only Tn916 was transferred, but Tn916 donor ability was not itself inheritable by the recipients and seemed to be associated with the presence of Tn916 on a non-conjugative pBR322-derived vector in the original donor strain. Transfer of Tn916 by conjugation was found to be an efficient method for producing insertion mutations in the chromosome of recipient cells. Although such insertions were unstable when the cells were grown under non-selective conditions, it was possible to show that over 40% of the isolated Tn916 insertions in the chromosome of E. coli K12 were in gene(s) concerned with histidine biosynthesis, implying that there is a partial hot-spot for Tn916 insertion on the E. coli K12 chromosome. When a strain of H. influenzae type b was used as a recipient, out of approximately 1500 transconjugants tested, two mutants were isolated with insertions in genes controlling the expression of iron-regulated transferrin-binding proteins. These mutants constitutively produced major 76 kDa and minor 90 kDa proteins which bound transferrin, even when grown under iron-sufficient conditions. Tn916 insertion mutagenesis, following transfer by conjugation, is a convenient method for isolating mutations in genes concerned with iron acquisition by this important human pathogen. 相似文献
10.
The observation that increased muscular activity leads to muscle hypertrophy is well known, but identification of the biochemical and physiological mechanisms by which this occurs remains an important problem. Experiments have been described (5, 6) which suggest that creatine, an end product of contraction, is involved in the control of contractile protein synthesis in differentiating skeletal muscle cells and may be the chemical signal coupling increased muscular activity and the increased muscular mass. During contraction, the creatine concentration in muscle transiently increases as creatine phosphate is hydrolyzed to regenerate ATP. In isometric contraction in skeletal muscle for example, Edwards and colleagues (3) have found that nearly all of the creatine phosphate is hydrolyzed. In this case, the creatine concentration is increased about twofold, and it is this transient change in creatine concentration which is postulated to lead to increased contractile protein synthesis. If creatine is found in several intracellular compartments, as suggested by Lee and Vissher (7), local changes in concentration may be greater then twofold. A specific effect on contractile protein synthesis seems reasonable in light of the work of Rabinowitz (13) and of Page et al. (11), among others, showing disproportionate accumulation of myofibrillar and mitochondrial proteins in response to work-induced hypertrophy and thyroxin-stimulated growth. Previous experiments (5, 6) have shown that skeletal muscles cells which have differentiated in vitro or in vivo synthesize myosin heavy-chain and actin, the major myofibrillar polypeptides, faster when supplied creatine in vitro. The stimulation is specific for contractile protein synthesis since neither the rate of myosin turnover nor the rates of synthesis of noncontractile protein and DNA are affected by creatine. The experiments reported in this communication were undertaken to test whether creatine selectively stimulates contractile protein synthesis in heart as it does in skeletal muscle. 相似文献