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1.
The method of limited tryptic proteolysis has been used to compare and contrast the substructure of bovine cardiac myosin subfragment 1 (S-1) to that of skeletal myosin S-1. While tryptic cleavage of cardiac S-1, like that of skeletal S-1, yields three fragments, the 25K, 50K, and 20K peptides, the digestion of cardiac S-1 proceeds at a 2-fold faster rate. The increased rate of cleavage is due entirely to an order of magnitude faster rate of cleavage at the 25K/50K junction of cardiac S-1 compared to that of skeletal, with approximately equal rates of cleavage at the 50K/20K junctions. Actin inhibits the tryptic attack at this latter junction, but its effect is an order of magnitude smaller for the cardiac than for the skeletal S-1. Furthermore, the tryptic susceptibility of the 50K/20K junction of cardiac S-1 in the acto-S-1 complex is increased in the presence of 2 mM MgADP. This effect is not due to partial dissociation of the cardiac acto-S-1 complex by MgADP. Our results indicate that in analogy to skeletal S-1, the cardiac myosin head is organized into three protease-resistant fragments connected by open linker peptides. However, the much faster rate of tryptic cleavage of the 25K/50K junction and also the greater accessibility of the 50K/20K junction in the cardiac acto-S-1 complex indicate substructural differences between cardiac and skeletal S-1. 相似文献
2.
Computer-based modeling of the conformation and packing properties of docosahexaenoic acid 总被引:10,自引:0,他引:10
We used a molecular modeling approach to search for a conformation of docosahexaenoic acid (DHA) that might uniquely influence acyl chain packing in cell membranes. Studies of DHA models containing six cis double bonds and five intervening methylene groups identified two conformations of special interest. Both had nearly straight chain axes formed by methylene carbon alignment. In one, the carbons of the six double bonds projected outward from the methylene axis in two nearly perpendicular planes to form an angle iron-shaped molecule. In the other, the double-bond carbons projected outward from the axis at nearly 90 degree-intervals to form a helix. Studies of packed arrays of these hexaenes with or without saturated hydrocarbons showed that tight intermolecular packing arrangements were possible, particularly in the case of the angle iron-shaped molecules. The planar surfaces of two or more such molecules could be brought into contact "back to back," while the interplanar "V groove" of each molecule could come into close apposition with a saturated chain. Because a similar mixed chain packing arrangement was found also for 1,2 diacylglycerols, these results raise the possibility that DHA may, in certain circumstances, promote tight, regular acyl chain packing arrays in DHA-rich membranes. 相似文献
3.
We have reported that tk-/- mutants recovered in the mouse L5178Y tk+/- 3.7.2C mutagen assay have often lost the tk+ allele. Allele loss in the tk-/- mutants is documented on Southern blots as the absence of a 6.3-kb Nco I fragment seen in both tk+/+ and tk+/- cell DNAs. For the routine screening of large- and small-colony tk-/- mutants DNAs for the absence of this genomic fragment, we have found that cells can be lysed in agarose plugs, and DNA of cells embedded in plugs can be purified, restricted with Nco I, electrophoresed, and analyzed on Southern blots without significant band distortion or diffusional loss of tk- specific fragments in the 2-7-kb range. Purification and restriction analysis of DNA in agarose plugs, originally developed to allow pulsed-field gel electrophoresis of very large DNA fragments, represents a convenient alternative to conventional DNA purification methods, allowing quantitative recovery of DNA from small numbers of cells, eliminating centrifugation, phenol extraction, and ethanol precipitation steps, and requiring smaller quantities of reagents. 相似文献
4.
Plasmid-mediated mineralization of naphthalene, phenanthrene, and anthracene. 总被引:12,自引:7,他引:5 下载免费PDF全文
The well-characterized plasmid-encoded naphthalene degradation pathway in Pseudomonas putida PpG7(NAH7) was used to investigate the role of the NAH plasmid-encoded pathway in mineralizing phenanthrene and anthracene. Three Pseudomonas strains, designated 5R, DFC49, and DFC50, were recovered from a polynuclear aromatic hydrocarbon-degrading inoculum developed from a manufactured gas plant soil slurry reactor. Plasmids pKA1, pKA2, and pKA3, approximately 100 kb in size, were isolated from these strains and characterized. These plasmids have homologous regions of upper and lower NAH7 plasmid catabolic genes. By conjugation experiments, these plasmids, including NAH7, have been shown to encode the genotype for mineralization of [9-14C]phenanthrene and [U-14C]anthracene, as well as [1-14C]naphthalene. One strain, Pseudomonas fluorescens 5RL, which has the complete lower pathway inactivated by transposon insertion in nahG, accumulated a metabolite from phenanthrene and anthracene degradation. This is the first direct evidence to indicate that the NAH plasmid-encoded catabolic genes are involved in degradation of polynuclear aromatic hydrocarbons other than naphthalene. 相似文献
5.
Relationships among the following taxa were examined based on 18S ribosomal RNA and DNA nucleotide sequences: Branchiopoda (Branchinecta packardi), Ostracoda (two podocopid species), Branchiura (Argulus nobilis), Pentastomida (Porocephalus crotali), Copepoda (Calanus pacificus, Macrocyclops albidus), Thoracica (Balanus eburneus, Calantica villosca), Acrothoracica (Trypetesa lampas), and Decapoda (Procambarus leonensis, Callinectes sapidus). Phylogenetic relationships were inferred by maximum parsimony and results evaluated by bootstrapping. With Branchinecta packardi as an outgroup, the following tree was inferred: the first branch leads to a node that joins a pentastome, a branchiuran and the two ostracodes; the second branch leads to a node that has the two copepods as a sister taxon to a clade that includes the acrothoracican and thoracicans; the last branch leads to a node joining the two decapods. The analyses suggest: (1) acrothoracicans diverged very early from the cirripede line and are not derived from a lepadomorph-like ancestor; (2) branchiurans are not related to either copepods or thecostracans but are closely allied with pentastomes; and (3) the Maxillopoda, broadly defined, is not a monophyletic taxon. These results differ from previous studies of these groups. 相似文献
6.
Stanley C. Deresinski Robert J. Applegate Hillel B. Levine David A. Stevens 《Cellular immunology》1977,32(1):110-119
In vitro stimulation of incorporation of tritiated thymidine by human peripheral lymphocytes in response to two soluble antigens and three different intact but nonviable fungal forms of Coccidioides immitis was studied. Lymphocytes were obtained from three groups of subjects: healthy skin test positive, healthy skin test negative, and disseminated disease. Dose-response relationships to the intact forms (endospores, arthrospores, and spherules) were determined. Responses of lymphocytes from healthy skin test-positive subjects and subjects with disseminated disease were similar. Ranking of antigens by “potency” gave the following results: endospores = spherulin > mycelial filtrate > arthrospores = spherules. Endospores were the most potent of the intact forms in 10 of 11 subjects. The clear superiority of endospores over spherules is not due to differences in the total particle surface area available for presentation to the leukocytes. All antigens tested except spherules could discriminate between skin test-positive and skin test-negative subjects in this in vitro system. A T-cell-enriched, B-cell- and mono-cyte-depleted cell population demonstrated an active response to spherulin and to endospores. The variance of these finding with animal studies demonstrating spherules to be immunogenically superior when compared to endospores is discussed. This may have importance in future studies in humans of vaccines to C. immitis. 相似文献
7.
Localization of the mouse thymidine kinase gene to the distal portion of chromosome 11 总被引:3,自引:0,他引:3
We report the cytogenetic mapping of the thymidine kinase (tk-1) gene in the mouse using two complementary and independent analyses: (1) investigation of chromosome aberrations associated with tk-1 gene inactivation in the L5178Y TK+/- -3.7.2C cell line, and (2) fluorescence in situ molecular hybridization of cloned tk-1 cDNA probes to mitotic chromosomes of this cell line. The consensus location from both analyses is 11E1-E2. Consideration of the mouse tk-1 gene localization, along with evidence that the homologous human TK1 gene is located distally on the large arm of chromosome 17, appears to extend the region of homology between MMU11 and HSA17 to the distal end of both chromosomes. 相似文献
8.
Kirsten M. Madsen C. William Applegate Dr. C. Craig Tisher 《Cell and tissue research》1982,226(2):363-374
Summary Morphological examination of kidney biopsies from patients with glomerulonephritis and hematuria has revealed the presence of erythrocytes within epithelial cells of the proximal tubule. This observation suggested that the proximal tubule might be capable of phagocytizing morphologically intact erythrocytes. To examine this possibility small quantities of heparinized autologous blood were injected into surface convolutions of proximal tubules of the rat kidney using standard micropuncture techniques. At time intervals ranging from 10 min to 120 h after injection, the kidneys were preserved for light and transmission electron microscopy by drip-fixation with a half-strength Karnovsky's glutaraldehyde-formaldehyde fixative.During the initial 6 h there was a flattening of the brush border and accumulation of electron-dense material representing hemoglobin in apical vacuoles and in lysosome-like structures. From 6 to 15 h after micropuncture, there was progressive loss of the brush border and the simultaneous formation of pseudopodia-like evaginations that extended from the apical plasma membrane and surrounded the individual erythrocytes. By 18 and 24 h, erythrocytes were observed in the proximal tubule cells. At later time intervals, edema, lymphocytic infiltration, and fibrosis were observed in the interstitium. In addition, crystalline structures were present in the lumen and the cells of both proximal and distal tubules. These findings suggest that in addition to their well-established ability to pinocytize hemoglobin and other proteins, the cells of the proximal tubule are capable of phagocytizing morphologically intact autologous erythrocytes. It is possible that phagocytosis by the proximal tubule cells may play a role in the disposal of erythrocytes from the tubular fluid in hematuric conditions. 相似文献
9.
A Chromosomally Based tod-luxCDABE Whole-Cell Reporter for Benzene, Toluene, Ethybenzene, and Xylene (BTEX) Sensing 总被引:2,自引:0,他引:2 下载免费PDF全文
A tod-luxCDABE fusion was constructed and introduced into the chromosome of Pseudomonas putida F1, yielding the strain TVA8. This strain was used to examine the induction of the tod operon when exposed to benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and aqueous solutions of JP-4 jet fuel constituents. Since this system contained the complete lux cassette (luxCDABE), bacterial bioluminescence in response to putative chemical inducers of the tod operon was measured on-line in whole cells without added aldehyde substrate. There was an increasing response to toluene concentrations from 30 μg/liter to 50 mg/liter, which began to saturate at higher concentrations. The detection limit was 30 μg/liter. There was a significant light response to benzene, m- and p-xylenes, phenol, and water-soluble JP-4 jet fuel components, but there was no bioluminescence response upon exposure to o-xylene. The transposon insertion was stable and had no negative effect on cell growth. 相似文献
10.