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101.
Effects of second order photobleaching on recovered diffusion parameters from fluorescence photobleaching recovery 下载免费PDF全文
In the original theoretical development of fluorescence photobleaching recovery with circular or Gaussian laser intensity profiles (Axelrod et al., 1976, Biophys. J.) the bleaching process is assumed to obey first order kinetics in the fluorescent probe. While this is reasonable in most cases where oxygen participates in the photolysis reaction, some processes may obey second order kinetics in the fluorophore concentration due to dimerization. Accordingly, we present here an analysis of the fluorescence recovery when the photobleaching process is taken to be second order in the probe. Analytical solutions for small bleaching levels indicate that the fluorescence recovery curve is very similar to that measured following a bleaching process first order in the probe. Numerical solutions for moderate bleaching levels show that the recovery is qualitatively similar, but quantitatively different. Because the shape of the recovery curve provides no evidence as to the order of photobleaching, we recommend continued use of the previous theoretical analysis. However, it must be borne in mind that the diffusion coefficient is increasingly underestimated as the extent of photobleaching is increased. The true diffusion coefficient is obtained in the limit of small levels of photobleaching. Estimates of the fractional recovery are not affected by this approach. 相似文献
102.
Sren Kragh Moestrup Keld Kaltoft Claus Munck Petersen Sren Pedersen Jrgen Gliemann Erik Ils Christensen 《Experimental cell research》1990,190(2)
The α2-macroglobulin receptor was recently purified from rat liver and human placenta. Three different monoclonal antibodies have now been raised against the human receptor and expression of the 440-kDa receptor protein is demonstrated in human placenta, fibroblasts, liver, and monocytes by immunoblot analysis. Flow cytometric studies showed that anti-α2-macroglobulin receptor monoclonal antibodies bind to 90–100% of the blood monocyte population and not to other blood cells. This defines the α2-macroglobulin receptor as a monocyte differentiation antigen, different from any of the classified leucocyte cluster determinants. Electron microscopic gold immunocytochemistry revealed the subcellular distribution of the receptor in human cultured monocytes and fibroblasts. In these cells, 18–33% of the gold particles were found on the outside of the plasma membrane, and in fibroblasts, especially, in coated invaginations. The intracellular receptors were mainly distributed in vesicles and tubular structures. 相似文献
103.
The in vivo capacity of urea nitrogen synthesis (CUNS) during alanine stimulation was measured within the blood amino acid concentration interval 7.3-11.6 mmol/l, where urea synthesis is at maximum and independent of substrate concentration. Three groups of rats were fed for 14 days, either a low protein diet (8%), a normal diet (17%), or a high protein diet (53%). Diet protein modified both CUNS and plasma glucagon concentration. CUNS was 5.86 +/- 2.93, 7.43 +/- 2.16, and 19.31 +/- 4.32 mumol/(min.100 g BW) (mean +/- SD, N = 6), respectively. The corresponding plasma glucagon concentrations after alanine stimulation were 222 +/- 400, 633 +/- 229, and 1700 +/- 627 ng/l, respectively. The in vivo kinetics of urea production is regulated by dietary protein, possibly via glucagon. This implies that the liver plays an active part in adaptation of whole body nitrogen homeostasis to dietary changes. 相似文献
104.
Quenching of the amidolytic activity of one-chain tissue-type plasminogen activator by mutation of lysine-416 总被引:1,自引:0,他引:1
In contrast to most other serine proteases, tissue-type plasminogen activator (t-PA) possesses enzymatic activity as the one-chain zymogen form. The hypothesis that lysine residues 277 or 416 may be involved in stabilization of an active conformation of one-chain t-PA via salt-bridge formation with aspartic acid residue 477 was tested by site-directed mutagenesis. Four recombinant t-PA mutants were constructed. The amidolytic activities of these analogues were compared to that of authentic t-PA. Substitution of arginine-275 provided an analogue [( R275G]t-PA) resistant to plasmin cleavage. The amidolytic activity of [R275G]t-PA was comparable to that of authentic one-chain t-PA, and so was the activity of [R275L,K277L]t-PA, in which additional substitution of lysine residue 277 was carried out. This suggested that its presence was nonessential for obtaining one-chain t-PA activity. In contrast, substitution of lysine residue 416 to obtain [K416S]t-PA and [K416S,H417T]t-PA resulted in substantial quenching of amidolytic one-chain activity. As expected, the amidolytic activities of the two-chain forms were less affected by the substitution. Involvement of lysine residue 416 in one-chain t-PA activity was also indicated by decreased activities of [K416S]t-PA and [K416S,H417T]t-PA with plasminogen as the substrate. The one-chain activity of the lysine residue 416 substitution analogues was partially restored in the presence of fibrin. This could indicate that strong ligands such as fibrin might provide an alternative stabilization of the active conformation of one-chain t-PA. 相似文献
105.
Purification of acetoacetate decarboxylase from Clostridium acetobutylicum ATCC 824 and cloning of the acetoacetate decarboxylase gene in Escherichia coli. 总被引:7,自引:1,他引:6 下载免费PDF全文
In Clostridium acetobutylicum ATCC 824, acetoacetate decarboxylase (EC 4.1.1.4) is essential for solvent production, catalyzing the decarboxylation of acetoacetate to acetone. We report here the purification of the enzyme from C. acetobutylicum ATCC 824 and the cloning and expression of the gene encoding the acetoacetate decarboxylase enzyme in Escherichia coli. A bacteriophage lambda EMBL3 library of C. acetobutylicum DNA was screened by plaque hybridization, using oligodeoxynucleotide probes derived from the N-terminal amino acid sequence obtained from the purified protein. Phage DNA from positive plaques was analyzed by Southern hybridization. Restriction mapping and subsequent subcloning of DNA fragments hybridizing to the probes localized the gene within an approximately 2.1 kb EcoRI/Bg/II fragment. A polypeptide with a molecular weight of approximately 28,000 corresponding to that of the purified acetoacetate decarboxylase was observed in both Western blots (immunoblots) and maxicell analysis of whole-cell extracts of E. coli harboring the clostridial gene. Although the expression of the gene is tightly regulated in C. acetobutylicum, it was well expressed in E. coli, although from a promoter sequence of clostridial origin. 相似文献
106.
We have used RNases T1, T2 and A to digest two aminoacyl-tRNAs, Escherichia coli Phe-tRNAPhe and E. coli Met- tRNAMetm both in the naked forms and in ternary complexes with E. coli elongation factor Tu (EF-Tu) and GTP. An analysis of the 'footprinting' results has led to an interpretation that has localized the part of the three-dimensional structure of aminoacyl-tRNA covered by the protein in the ternary complex. In terms of the three-dimensional structure of tRNA established for yeast tRNAPhe, EF-Tu covers the aa-end, aa-stem, T-stem, and extra loop on the side of the L-shaped tRNA that exposes the extra loop. 相似文献
107.
Elongation factor EF-Tu from Escherichia coli was labelled with N-[14C]tosyl-L-phenylalanylchloromethane, digested with trypsin and the peptides obtained separated by HPLC. The only radioactive peak recovered corresponded to tryptic peptide containing residues 75–98. Sequencing of the peptide by automated Edman degradation identified cysteine 81 as the site of N-tosyl-L-phenylalanylchloromethane modification. These results confirm the importance of this residue for the interaction with aminoacyl-tRNAs. 相似文献
108.
E A Petersen L E Greenberg T Manzara C H Kirkpatrick 《Journal of immunology (Baltimore, Md. : 1950)》1981,126(6):2480-2484
A model for studying transfer of delayed-type sensitivity to mice with cellfree materials is described. The results with a particulate antigen (Candida) and 4 soluble protein antigens (PPD, ferritin, cytochrome c, and horseradish peroxidase) suggest that the phenomenon is antigen specific. Identical preparations from the spleens of insensitive donors were not active. This murine model should facilitate characterization of the immunologic and chemical properties of transfer factor. 相似文献
109.
James J. Petersen 《Journal of nematology》1980,12(1):45-48
When numbers of Romanomermis culicivorax Ross and Smith were varied in containers with a constant surface area and depth of sand, densities of 12-24 nematodes per cm² yielded significantly more preparasites than higher densities. When container surface area and numbers of nematodes were constant and sand volume and depth were varied, yields did not differ significantly. When numbers of nematodes and sand volume were constant and surface area and sand depths were varied, yields were significantly higher for a density of 24 nematodes per cm². Yields of preparasites were tripled by simply setting up three cultures, each containing 5 g of nematodes, instead of a single culture containing 15 g. 相似文献
110.