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991.
Three fluorescent dinucleoside phosphates containing 1,N6-ethenoadenosine (εA), εApεA, εApεC, and εApU were studied using fluorescence-detected circular dichroism (FDCD), circular dichroism (CD), and absorption measurements. The FDCD data indicate that εApεC and εApU can be described as two-state systems consisting of a fluorescent species and a stacked, nonfluorescent species. Thermodynamic stacking parameters are calculated for these molecules using the van't Hoff equation. εApεA is found to be a more complicated system with a fluorescent CD which is different in shape, but comparable in magnitude, to the conventional CD of the dimer. This molecule, unlike the other two dinucleoside phosphates, cannot be characterized as a two-state system; it is described as consisting of at least three states at temperatures above 35°C. The CD data were subjected to a linear analysis in order to determine the minimum number of states present. In agreement with the FDCD data, εApεC and εApU are found to consist of a minimum of two states, while εApεA is indicated to have at least three. The more complicated behavior of the latter dimer is also indicated by the values of the unstacked CD obtained in the van't Hoff analysis. 相似文献
992.
Calcitonin stimulates plasminogen activator in porcine renal tubular cells: LLC-PK1 总被引:5,自引:0,他引:5 下载免费PDF全文
J M Dayer J D Vassalli J L Bobbitt R N Hull E Reich S M Krane 《The Journal of cell biology》1981,91(1):195-200
Plasminogen activators are highly selective proteases that activate the proenzyme plasminogen to the general protease, plasmin. We studied a porcine kidney cell line, originally isolated as a high producer of plasminogen activator, in which activities of cellular adenylate cyclase and cAMP-dependent protein kinase are increased in response to calcitonin. We found that salmon calcitonin, in the concentration range 0.03-300 nM, increased plasminogen activator production up to approximately 1,000-fold and concurrently inhibited cell multiplication; both of these effects were reversible. Human calcitonin was approximately 0.01 times as potent as salmon calcitonin, corresponding to potency differences observed in other biological systems. Plasminogen activator production was also stimulated by other agents that raise cellular cAMP levels such as cholera toxin, phosphodiesterase inhibitors, and vasopressin, but not to the same extent as by calcitonins. The rapidity and sensitivity of the plasminogen activator determination and other cellular responses may make it possible in the future to use this cell stain in a convenient bioassay for calcitonins and their analogues. 相似文献
993.
Topical application of JHA to fifth instar nymphs of Oncopeltus fasciatus, immediately following ecdysis from the fourth instar, decreases the duration of the fifth instar by approximately 36 hr in addition to inducing a supernumerary larval moult. JHA appears to accelerate the time of subsequent ecdysis in two ways: first, the onset of ecdysone secretion is accelerated, and is accompanied by a similarly premature initiation of mitotic activity in epidermal cells. This is the classical prothoracicotropic action of JH. Second, the period between the onset of mitotic activity and the time of ecdysis itself is shortened. That is, once cellular activities associated with the moulting cycle are triggered by ecdysone, such activities are completed more rapidly in the presence of JHA. It appears that the larval-larval moult induced by JHA requires intrinsically less time to accomplish than a normal metamorphic moult. 相似文献
994.
Wendy Love Donna Millay James S. Huston 《Archives of biochemistry and biophysics》1981,207(2):300-310
This investigation pursued aspects of tubulin structure using limited tryptic digestion as a sensitive monitor of conformational state. A novel form of tubulin was analyzed that had been purified on hydroxyapatite in sodium phosphate buffer and exhibited interchain disulfide crosslinking. Circular dichroism spectra of this protein were highly reproducible and indicate it assumes a stable native state. Limited proteolysis of bovine brain microtubule protein in its assembled or disassembled states yielded a prominent 41,000-molecular-weight product as long as it was stabilized by GTP-containing buffers. Hydroxyapatite-purified tubulin yielded entirely different limited digestion products, with species having molecular weights of 48,000 and several between 35,000 and 19,000. Limited proteolysis was found to offer a useful probe of tubulin structure and to produce fragments which might prove valuable in analyzing its protein substructure. Discussion is given on the relevance of these results to the structural state assumed by tubulin and to the conformation of disulfide-linked tubulin reported to reside in the postsynaptic density. 相似文献
995.
996.
Evidence is presented that when E. coli B is mixedly infected with T4D wild type and rII deletion mutants, the excess DNA of the wild type allele is lost. No loss is seen in mixed infections with rII point mutants and wild type. In similar experiments with lysozyme addition mutants, the mutant allele is lost. We believe these results demonstrate a repair system which removes "loops" in heteroduplex DNA molecules. A number of phage and host functions have been tested for involvement in the repair of the excess DNA, and T4 genes x and v have been implicated in this process. 相似文献
997.
The acid and enzymic hydrolysis of O-acetylated sialic acid residues from rabbit Tamm–Horsfall glycoprotein 下载免费PDF全文
Rabbit Tamm-Horsfall glycoprotein and bovine submaxillary glycoprotein were both found to contain sialic acid residues which are released at a slow rate by the standard conditions of acid hydrolysis. These residues are also resistant to neuraminidases from Vibrio cholerae and Clostridium perfringens. This behaviour was attributed to the presence of O-acetylated sialic acid, since the removal of O-acetyl groups by mild alkaline treatment normalized the subsequent release of sialic acid from rabbit Tamm-Horsfall glycoprotein by acid and by enzymic hydrolysis. Determination of the O-acetyl residues in rabbit Tamm-Horsfall glycoprotein indicated that on average two hydroxyl groups of sialic acid are O-acetylated, and these were located on the polyhydroxy side-chain of sialic acid or on C-4 and C-8. These findings confirm the assumption that certain O-acetylated forms of sialic acid are not substrates for bacterial neuraminidases. Several explanations have been suggested to explain the effect of O-acetylation of the side-chain on the rate of acidcatalysed hydrolysis of sialic acid residues. 相似文献
998.
Rothe R. Kaplan A. Lein Harte H. Nachtscheim Sartorius H. Hirsch H. Marquardt A. Reitberger K. Egle Straub Schwanitz E. Siebs Nolte H. Reich 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1954,24(6):181-184
Ohne Zusammenfassung 相似文献
999.
Somerson, Norman L. (National Institutes of Health, Bethesda, Md.), Paul R. Reich, Barbara E. Walls, Robert M. Chanock, and Sherman M. Weissman. Genetic differentiation by nucleic acid homology. II. Genotypic variations within two Mycoplasma species. J. Bacteriol. 92:311-317. 1966.-A deoxyribonucleic-ribonucleic acid (DNA-RNA) homology technique was used to determine genetic relatedness among the nucleic acids of eight mycoplasmas which were serologically classified as Mycoplasma hominis type 1. The DNA preparations from these organisms were each found to be distinct. No subgrouping of the M. hominis type 1 strains could be demonstrated. In contrast, when the nucleic acids from six serologically related mycoplasmas which were isolated from tissue cultures were studied, the DNA from these species could not be distinguished. The DNA buoyant densities of the tissue culture isolates were similar. These isolates were closely related genetically to a porcine mycoplasma, M. hyorhinis. 相似文献
1000.
The pi form of glutathione-S-transferase (GST), previously found to be oligodendrocyte associated, has also been found in myelin. In the brains of adult mice, immunocytochemical staining for a pi form of GST was observed in myelinated fibers, as well as oligodendrocytes. In contrast, and as previously found in rats, positive immunostaining for mu forms occurred in astrocytes and not in oligodendrocytes or myelinated fibers. Double immunofluorescence staining strengthened the conclusion that pi was in oligodendrocytes and myelin in mouse brains. The results of enzyme assays performed on brain homogenates and purified myelin indicated that GST specific activities in mouse brain myelin were almost as high (0.8-fold) as those in mouse brain homogenates. Low, but reproducible, GST activities were also observed in myelin purified from rat brains, in which pi had been demonstrated in oligodendrocytes and mu in astrocytes. The pi form was also stained by the immunoblot technique in myelin purified from mouse brain. It was concluded that pi is a myelin associated, as well as oligodendrocyte associated, enzyme in mouse brain, and possibly also in rat brain. This is the first report of localization of GSTs in mouse brain and of GST in myelin. 相似文献