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81.
Allosteric Modulation of Flunitrazepam Binding to Rat Brain Benzodiazepine Receptors by Methyl β-Carboline-3-Carboxylate 总被引:4,自引:3,他引:1
The inhibition of flunitrazepam (FNP) binding to rat brain benzodiazepine (BZ) receptors by methyl beta-carboline-3-carboxylate (MCC) was studied. Biphasic dissociation was observed for [3H]FNP and [3H]MCC in cerebral cortex, cerebellum, and hippocampus, although the dissociation of [3H]MCC was much faster. The dissociation rate of [3H]FNP was increased by MCC in the cerebellum, but was not altered in cerebral cortex or hippocampus. [3H]FNP binding stimulated by gamma-aminobutyric acid was enhanced in the presence of MCC in all three regions examined. These results indicate that MCC exerts these effects by interacting with allosteric sites that are different from the FNP recognition sites on the BZ receptors. 相似文献
82.
Ethanol extracts of Myxococcus xanthus contained several substances, referred to as autocides, which were bactericidal to the producing strain but showed no activity against other bacteria. The autocides were produced by growing cells and remained largely cell bound throughout the growth cycle; ca. 5% of the autocidal activity was found in the supernatant fluid at the time cell lysis began. The autocides were separated by sequential-column and thin-layer chromatography into five active fractions (AM I through AM V). Each of the fractions was at least 20 times more active against M. xanthus than against the other gram-negative or gram-positive bacteria tested. AM I, AM IV, and AM V were inactive against yeasts, whereas a mixture of fractions AM II and AM III was active against Rhodotorula sp. At low concentrations, AM I reversibly inhibited the growth of M. xanthus; at higher concentrations of AM I, the cells lysed within 1 h. The lowest concentration of AM IV that showed any activity caused rapid cell death and lysis. The mode of action of the major autocide, AM V, was different from that of AM I and AM IV. During the initial 2 h of treatment, the viable count of M. xanthus cells remained constant; during the next few hours killing occurred without lysis; within 24 h lysis was complete. The autocidal activity of each of the fractions was expressed when the cells were suspended in buffer, as well as in growth medium. The possible role of autocides in developmental lysis of M. xanthus is discussed. 相似文献
83.
Transfer of Rhizobium meliloti pSym genes into Agrobacterium tumefaciens: host-specific nodulation by atypical infection 总被引:27,自引:18,他引:9 下载免费PDF全文
G Truchet C Rosenberg J Vasse J S Julliot S Camut J Denarie 《Journal of bacteriology》1984,157(1):134-142
The pSym megaplasmid of Rhizobium meliloti 2011 mobilized by plasmid RP4, or plasmid pGMI42, an RP4-prime derivative which carries a 290-kilobase pSym fragment including nitrogenase and nod genes, was introduced into Agrobacterium tumefaciens. The resulting transconjugants induced root deformations specifically on the homologous hosts Medicago sativa and Melilotus alba and not on the heterologous hosts Trifolium pratense and Trifolium repens. The root deformations were shown to be genuine nodules by physiological and cytological studies. Thus, host specificity nodulation genes are located on the pSym megaplasmid. Host nodulation specificity did not seem to require recognition at the root hair level since no infection threads could be detected in the root hairs. Cytological observations indicated that bacteria penetrated only the superficial layers of the host root tissue by an atypical infection process. The submeristematic zone and the central tissue of the nodules were bacteria free. Thus, nodule organogenesis was probably triggered from a distance by the bacteria. Agrobacterium transconjugants carrying pSym induced the formation of more numerous and larger nodules than those carrying the RP4-prime plasmid pGMI42, suggesting that some genes influencing nodule organogenesis are located in a pSym region(s) outside that which has been cloned into pGMI42. 相似文献
84.
The phosphate moiety of D-mannitol-1-phosphate in Escherichia coli is subject to rapid turnover and is in close equilibrium with Pi and the phosphorus of fructose-1,6-bisphosphate. These three compounds account for the bulk of 32P label found in cells after several minutes of uptake of 32Pi and mannitol-1-phosphate represents some 30% of this label. Mannitol-1-phosphate occurs in E. coli grown on a variety of carbon sources, in the absence of D-mannitol, and is synthesized de novo even in mutants lacking mannitol-1-phosphate dehydrogenase. The mannitol moiety of mannitol-1-phosphate was not affected during the total chase of the P moiety, which exchanged with a half-life of about 30 s. These findings suggest that the rapid equilibration of the phosphorus is a function of an enzyme, possibly a component of the phosphotransferase system, capable of forming a complex that allows the exchange of the phosphate without the equilibration of the mannitol moiety with free mannitol. 相似文献
85.
Q Q Zhuang S Rosenberg J Lawrence A Stracher 《Biochemical and biophysical research communications》1984,118(2):508-513
Actin binding protein from human blood platelets is shown to exist in the resting platelet as a phosphorylated protein and contains two residues of phosphate per 260,000 kd. Removal of one-half of these residues with E. coli alkaline phosphatase results in the loss of its ability to crosslink F-actin into a low speed sedimentable complex (its cytoskeleton) and to bind to an F-actin affinity column. Thus, phosphorylation-dephosphorylation of ABP may be an important regulatory mechanism by which the platelet regulates its shape via its cytoskeletal structure. 相似文献
86.
Only site-directed antibodies reactive with the highly conserved src-homologous region of the v-abl protein neutralize kinase activity 总被引:37,自引:9,他引:28 下载免费PDF全文
J B Konopka R L Davis S M Watanabe A S Ponticelli L Schiff-Maker N Rosenberg O N Witte 《Journal of virology》1984,51(1):223-232
Antisera specific for six regions of the v- abl protein were used to serologically characterize the Abelson murine leukemia virus tyrosine kinase. Chemically synthesized peptides corresponding to the predicted v- abl protein sequence and larger regions of the v- abl protein expressed as fusion proteins in bacteria were used as immunogens. The specificity of each antiserum was confirmed by immunoprecipitation analysis with defined deletion mutants of Abelson murine leukemia virus. Several of these v- abl -specific antisera display much higher titers and avidities than serum harvested from mice bearing Abelson murine leukemia virus-induced tumors, previously the only source of anti- abl -specific serum. Two antisera were found to block the in vitro autophosphorylation of the v- abl protein as well as its ability to phosphorylate a peptide substrate. Examination of the sites against which the kinase-blocking antisera were prepared revealed that both are in close proximity to the in vivo sites of tyrosine phosphorylation, which fall within the region of high homology with v-src and other tyrosine kinases. Antisera directed against other regions of v- abl did not inhibit kinase activity. 相似文献
87.
William H. Karasov Edwin Petrossian Laura Rosenberg Jared M. Diamond 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1986,156(4):599-609
Summary What digestive adaptations permit herbivorous nonruminant mammals to sustain much higher metabolic rates than herbivorous lizards, despite gross similarity in digestive anatomy and physiology? We approached this question by comparing four herbivorous species eating the same diet of alfalfa pellets: two lizards (chuckwalla and desert iugana) and two mammals (desert woodrat and laboratory mouse). The mammals had longer small and large intestines, greater intestinal surface area, much higher (by an order of magnitude) food intake normalized to metabolic live mass, and much faster food passage times (a few hours instead of a few days). Among both reptiles and mammals, passage times increase with body size and are longer for herbivores than for carnivores. The herbivorous lizards, despite these much slower passage times, had slightly lower apparent digestive efficiencies than the mammals. At least for chuckwallas, this difference from mammals was not due to differences in body temperature regime. Comparisons of chuckwallas and woodrats in their assimilation of various dietary components showed that the woodrat's main advantage lay in greater assimilation of the dietary fiber fraction. Woodrats achieved greater fiber digestion despite shorter residence time, but possibly because of a larger fermentation chamber, coprophagy, and/or different conditions for microbial fermentation. We conclude with a comparative overview of digestive function in herbivorous lizards and mammals, and with a list of four major unsolved questions. 相似文献
88.
Lillian Recant Nancy R. Voyles Kim I. Timmers Carla Zalenski Meira Fields S. J. Bhathena 《Peptides》1986,7(6):1061-1069
Free enkephalins (enk) and higher molecular weight enkephalin-containing peptides (enk-c-p) are present in the endocrine pancreas of rats, presumably in B cells. To determine whether these opioid peptides show dynamic alterations as insulin content of pancreas changes, we utilized a copper deficient rat model, in which the exocrine pancreas atrophies and the endocrine pancreas is “intact” and insulin (IRI) content increases. Dietary copper deficiency (−C) was produced in weanling male rats for 4 and 7 weeks. The deficient and copper supplemented (+C) groups were further subdivided to receive all dietary carbohydrate as either 62% fructose (F) or 62% starch (S). −CF rats showed the most severe deficiency. After 7 weeks, total units of pancreatic IRI in −CF were 7.5, +CF 2.1, −CS 7.9 and in +CS 2.8 (p<0.001). Pancreatic content of Met5- and Leu5-enk was measured in extracts which were purified on C-18 Seppaks with and without prior treatment with trypsin and carboxypeptidase B. −C animals showed progressive, significant increases in pancreatic content of Leu-enk-c-p, with a decrease in free Leu- and Met-enk (p<0.02-0.01). The pancreatic findings are compatible with a co-localization of enkephalins and insulin in the endocrine pancreas and are suggestive of co-regulation. 相似文献
89.
Abelson murine leukemia virus (A-MuLV) infection of mouse bone marrow cells usually leads to transformation of pre-B cells. However, when the environment is modified by the continuous presence of lipopolysaccharide (LPS), two novel types of membrane immunoglobulin (mIg)-positive B cell lines are generated. Because the cells which give rise to these cell lines copurify with mIg-positive bone marrow cells, the cell lines arise as a result of A-MuLV interaction with a new type of in vitro target cell. The cell lines generated fall into two groups which differ in several phenotypic characteristics. Group 1 cells are more differentiated than the typical pre-B cell transformant in that they synthesize mIgM and appear to resemble virgin B cells. The group 1 cells do not secrete immunoglobulin and are independent of LPS for growth. In addition, these cell lines synthesize the Abelson P160 protein, contain integrated abl proviral DNA, and are highly tumorigenic in syngeneic animals. The group 2 cell lines differ markedly from both the group 1 cells and from typical, pre-B cell A-MuLV transformants. These cells are mIgG positive and secrete large amounts of immunoglobulin into the culture medium. The cell lines are comprised of both adherent and nonadherent cells and do not synthesize P160 or contain integrated v-abl sequences. The group 2 cells are nontumorigenic in syngeneic animals and require LPS for growth and viability. Both types of cells have remained in culture for over 2 years with no changes in their phenotypic characteristics. This A-MuLV infection system and the novel mIg-positive cell lines may serve as useful models for studying biochemical and molecular properties of mature B cells. 相似文献
90.
Regulation of the yeast metallothionein gene 总被引:3,自引:0,他引:3
To study regulation of the yeast CUP1 gene, we have employed plasmids containing the CUP1 regulatory sequences fused to the Escherichia coli galK gene. A comparison of galK expression from low- and high-copy-number CUP1/galK fusion plasmids demonstrated that both basal and induced levels of galactokinase (GalK) increase proportionately with plasmid copy number. Host strains with an amplified, single or deleted CUP1 locus were compared to look for effects of chromosomal CUP1 gene dosage on expression from the episomal CUP1 promoter. Basal GalK levels are similar in CUP1R and cupls hosts, but can be induced to higher levels in the cup1s than the CUP1R host. In contrast, in a strain deleted for the chromosomal copy of CUP1, synthesis of GalK is constitutive but can be induced to yet higher levels by copper. A hybrid vector, placing the CUP1 coding sequence under the control of a constitutive promoter, was constructed. Introduction of this hybrid CUP1 gene into the deletion host containing the CUP1/galK plasmid restores regulation. Thus, metallothionein, in trans, can effect repression of the CUP1 promoter. The possible roles of metallothionein and free copper in CUP1 regulation are discussed. 相似文献