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81.
82.
R Hsu S J Singer P Keim T F Deuel R L Heinrikson 《Archives of biochemistry and biophysics》1977,178(2):644-651
A new procedure for the isolation of Bacillus subtilis glutamine synthetase in a high state of purity is described. Automated Edman degradation of the reduced and carboxy-methylated protein revealed a single NH2-terminal amino acid sequence: H2N-Ala-Lys- Tyr-Thr-Arg5-Glu-Asp-Ile-Gln-Lys10-Leu-Val-Ser-Glu-Ser15-CM-Cys-Val-Thr- Tyr-Ile20-Ser-Leu-Gly-Phe-Ser25-Asn-Ser-Leu-Gly- -. The recovery of phenylthiohydantoin(PTH)-amino acids and the single sequence obtained are consistent with the view that the dodecameric enzyme of molecular weight 600,000 is composed of identical subunits. Earlier observations of multiple sequences (80% PTH-Ala and 20% PTH-Gly as NH2 terminal residues) appear to have been due to impurities removed by the final purification step described herein, which involves column chromatography on hydroxyapatite. Evidence for the existence of one disulfide bond and two free cysteine residues per subunit of dodecameric glutamine synthetase was obtained by alkylation of the denatured enzyme in the presence and absence of reducing agents. This distribution of the four cysteine residues in the enzyme monomer was confirmed by titration of the enzyme denatured in sodium dodecyl sulfate with 5,5′-dithiobis(2-nitrobenzoic acid). 相似文献
83.
D J McCance P G Walker J L Dyson D V Coleman A Singer 《BMJ (Clinical research ed.)》1983,287(6395):784-788
Twenty two patients referred to a district colposcopy clinic because of an abnormal cervical cytology report or a suspicious cervix and found to have a cervical epithelial abnormality were studied. The techniques of cytology, histology, immunohistochemistry, and DNA-DNA hybridisation were used to detect infection by human papillomavirus. Using an indirect immunoalkaline phosphatase technique human papillomavirus antigen was found in biopsy specimens from six of the 22 patients and DNA of papillomavirus type 6 in biopsy specimens from 13 of these women, including four out of six whose histological diagnosis was cervical intraepithelial neoplasia grade 3. In eight cases where cytological, colposcopical, and histological investigations all indicated the presence of wart virus infection, papillomavirus type 6 DNA was found in seven. Papillomavirus type 6 DNA was found in more than half of the proved cases of cervical intraepithelial neoplasia. The presence of this viral DNA in women with no cervical abnormality is to be studied. 相似文献
84.
S T Ohnishi K Hashimoto T Sato M T Devlin M Singer 《Canadian journal of physiology and pharmacology》1982,60(2):148-153
Dichloroisoproterenol (DCI) and propranolol were found to inhibit sickling in vivo when they were added to red-cell suspensions prior to deoxygenation. The effectiveness was maximal between PO2's of 30 and 40 mmHg (1 mmHg = 133.322 Pa). When cells were sickled at a low oxygen tension (PO2 = 32 mmHg), and then DCI was added later, the drug decreased the degree of sickling while the suspension was maintained at the same oxygen tension. The antisickling effect of these drugs was not antagonized by isoproterenol, a beta-adrenergic stimulator, by the addition of cAMP or increase of the intracellular calcium concentration. Other beta-blockers, such as MJ1999 (sotalol) and timolol, did not show antisickling activity. It was also found that DCI, propranolol, and timolol had some effect on the delay time of gelation of sickle-cell hemoglobin (Hb S), as well as on the oxygen affinity of sickle cells. 相似文献
85.
86.
The complement binding-like domains of the murine homing receptor facilitate lectin activity
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S R Watson Y Imai C Fennie J Geoffrey M Singer S D Rosen L A Lasky 《The Journal of cell biology》1991,115(1):235-243
The leukocyte homing receptor (HR), the endothelial leukocyte adhesion molecule, and gmp140/platelet activation-dependent granule membrane protein are members of a family of adhesion molecules, termed the lectin cell adhesion molecules (LEC-CAMS) which are unified by a multi-domain structure containing a lectin motif, an epidermal growth factor-like (egf) motif, and variable numbers of a complement binding-like (CB) motif. Previous data have indicated a predominant role for the lectin motif in cell adhesion directed by the LEC-CAMS, although the egf-like domain of the HR may also play a potential role in cell binding. While the role(s) of the CB domains in the LEC-CAMS is currently not understood, they have been hypothesized to act as rigid spacers or stalks for lectin and perhaps, egf domain presentation. In this paper, we analyze the functional characteristics of murine HR-IgG chimeras containing the lectin, lectin plus egf, and lectin plus egf plus CB domains. The Mel 14 mAb, an adhesion blocking antibody which recognizes a conformational determinant in the N-terminus of the HR lectin domain, shows a significantly decreased affinity for a HR construct which lacks the CB motifs, consistent with the possibility that the CB domains are involved with lectin domain structure. In agreement with this conjecture, HR mutants lacking the CB domains show a profound decrease in lectin-specific interaction with the carbohydrate polyphosphomannan ester, suggesting that the changes in Mel 14 affinity for the lectin domain are reflected in lectin functionality. Various assays investigating the interactions between the HR deletion mutants and the peripheral lymph node high endothelium, including cell blocking, immunohistochemical staining, and radioactively labeled ligand binding, all showed that removal of the CB domains results in a lack of HR adhesive function. These results imply that the CB domains of the HR, and, by analogy, the other members of the LEC-CAM family, may play important structural roles involving induction of lectin domain conformation and resultant functionality. 相似文献
87.
Y Takahama S O Sharrow A Singer 《Journal of immunology (Baltimore, Md. : 1950)》1991,147(9):2883-2891
A novel thymocyte subpopulation expressing an unusual TCR repertoire was identified by high surface expression of the Ly-6C Ag. Ly-6C+ thymocytes were distributed among all four CD4/CD8 thymocyte subsets, and represented a readily identifiable subpopulation within each one. Ly-6C+ thymocytes express TCR-alpha beta, arise late in ontogeny, and appear in the CD4/CD8 developmental pathway after birth in a sequence that resembles that followed by conventional Ly-6C- cells during fetal ontogeny. Most interestingly, adult Ly-6C+ thymocytes express an unusual TCR-V beta repertoire that is identical to that expressed by CD4-CD8-TCR-alpha beta+ thymocytes in its overexpression of TCR-V beta 8 and in its expression of some potentially autoreactive TCR-V beta specificities. This unusual TCR-V beta repertoire was even expressed by Ly-6C+ thymocytes contained within the CD4+ CD8- 'single positive' thymocyte subset. Thus, expression of this unusual TCR-V beta repertoire is not limited to CD4-CD8-thymocytes, and is unlikely to be a consequence of their double negative phenotype. Rather, we think that Ly-6C+TCR-alpha beta+ thymocytes and CD4-CD8-TCR-alpha beta+ are developmentally interrelated, a conclusion supported by several lines of evidence including the selective failure of both Ly-6C+ and CD4-CD8-TCR-alpha beta+ thymocyte subsets to appear in TCR-beta transgenic mice. In contrast, peripheral Ly-6C+ T cells are developmentally distinct from Ly-6C+ thymocytes in that peripheral Ly-6C+ T cells expressed a conventional TCR-V beta repertoire and developed normally in TCR-beta transgenic mice in which Ly-6C+ thymocytes failed to arise. We conclude that: 1) expression of a skewed TCR-V beta repertoire is a characteristic of Ly-6C+TCR-alpha beta+ thymocytes as well as CD4-CD8-TCR-alpha beta+ thymocytes, and is not unique to thymocytes expressing neither CD4 nor CD8 accessory molecules; and 2) Ly-6C+ thymocytes are developmentally linked to CD4-CD8-TCR-alpha beta+ thymocytes, but not to Ly-6C+ peripheral T cells. We suggest that Ly-6C+TCR-alpha beta+ thymocytes are not the developmental precursors of Ly-6C+ peripheral T cells, but rather may be the developmental precursors of CD4-CD8-TCR-alpha beta+ thymocytes. 相似文献
88.
Duplicate DNA sequences in the genome of Neurospora crassa can be detected and mutated in the sexual phase of the life cycle by a process termed RIP (repeat-induced point mutation). RIP occurs in the haploid nuclei of fertilized, premeiotic cells before fusion of the parental nuclei. Both copies of duplications of gene-sized sequences are affected in the first generation at frequencies of approximately 50-100%. We investigated the extent to which sequences altered by RIP remain susceptible to this process in subsequent generations. Duplications continued to be sensitive to RIP, even after six generations. The fraction of progeny showing evidence of RIP decreased rapidly, however, apparently as a function of the extent of divergence of the duplicated sequences. Analysis of the stability of heteroduplexes of DNA altered by RIP and their native counterpart indicated that linked duplications diverged further than did unlinked duplications. DNA methylation, a common feature of sequences altered by RIP, did not seem to inhibit the process. A sequence that had become resistant to RIP was cloned and reintroduced into Neurospora in one or more copies to investigate the basis of the resistance. The altered sequence regained its methylation in vegetative cells, indicating that the methylation of sequences altered by RIP observed in vegetative cells is a consequence of the mutations. Duplication of the sequence restored its sensitivity to RIP suggesting that resistance to the process was due to loss of similarity between the duplicated sequences. Consistent with this, we found that the resistant sequence did not trigger RIP of the native homologous sequences of the host, even when no other partner was available. High frequency intrachromatid recombination, which is temporally associated with RIP, was more sensitive than RIP to alterations in the interacting sequences. 相似文献
89.
Sara Brosh Oded Sperling Esther Dantziger Yechezkel Sidi 《Journal of neurochemistry》1992,58(4):1485-1490
The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
90.
E Corvera O G Mouritsen M A Singer M J Zuckermann 《Biochimica et biophysica acta》1992,1107(2):261-270
The model of Cruzeiro-Hansson et al. (Biochim. Biophys. Acta (1989) 979, 166-1176) for lipid-cholesterol bilayers at low cholesterol concentrations is used to predict the thermodynamic properties and the passive ion permeability of lipid bilayers as a function of acyl-chain length and cholesterol concentration. Numerical simulations based on the Monte Carlo method are used to determine the equilibrium state of the system near the main gel-fluid phase transition. The permeability is calculated using an ansatz which relates the passive permeability to the amount of interfaces formed in the bilayer when cholesterol is present. The model predicts at low cholesterol contents an increase in the membrane permeability in the transition region both for increasing cholesterol concentration and for decreasing chain length at a given value of the reduced temperature. This is in contrast to the case of lipid bilayers containing high cholesterol concentrations where the cholesterol strongly suppresses the permeability. Experimental results for the Na+ permeability of C15PC and DPPC (C16PC) bilayers containing cholesterol are presented which confirm the theoretical predictions at low cholesterol concentrations. 相似文献