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The relationships between the mean rectified EMG from two muscle groups crossing the knee joint and the rotational stiffness and laxity about the longitudinal axis of the lower leg were investigated. The EMG signals from three of the quadricep muscle group and two of the hamstring muscle group were monitored using surface electrodes. Each subject sustained self-induced muscle activity from specific muscle combinations while the foot was twisted internally and externally by the researcher. Joint rotation was measured using an electrogoniometer. Analyses of the data showed increased joint stiffness with increased numbers of active muscles. The stiffness measurements ranged from 0.16 to 2.54 Nm degree-1 depending upon the combination of active muscles. The stiffness measured in different tests were very repeatable with standard deviations ranging from 0.02 to 0.25 Nm degree-1. Increases in joint stiffness of over 400% by activation of these muscles were measured. 相似文献
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Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin 总被引:2,自引:0,他引:2 下载免费PDF全文
RK Draper D Chin D Eurey-Owens IE Scheffler MI Simon 《The Journal of cell biology》1979,83(1):116-125
We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells. 相似文献
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B Halliwell M L Hu S Louie T R Duvall B K Tarkington P Motchnik C E Cross 《FEBS letters》1992,313(1):62-66
Nitrogen dioxide (NO2.) is often present in inhaled air and may be generated in vivo from nitric oxide. Exposure of human blood plasma to NO2. caused rapid losses of ascorbic acid, uric acid and protein thiol groups, as well as lipid peroxidation and depletions of alpha-tocopherol, bilirubin and ubiquinol-10. No increase in protein carbonyls was detected. Supplementation of plasma with ascorbate decreased the rates of lipid peroxidation, alpha-tocopherol depletion and loss of uric acid. Uric acid supplementation decreased rates of lipid peroxidation but not the loss of alpha-tocopherol. We conclude that ascorbic acid, protein -SH groups, uric acid and alpha-tocopherol may be important agents protecting against NO2. in vivo. If these antioxidants are depleted, peroxidation of lipids occurs and might contribute to the toxicity of NO2.. 相似文献
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P M Jordan M J Warren B I Mgbeje S P Wood J B Cooper G Louie P Brownlie R Lambert T L Blundell 《Journal of molecular biology》1992,224(1):269-271
Porphobilinogen deaminase, the polymerase that catalyses the synthesis of preuroporphyrinogen, the linear tetrapyrrole precursor of uroporphyrinogen III, has been crystallized from sodium acetate buffer with polyethylene glycol 6000 as precipitant. The crystals are orthorhombic and the space group is P2(1)2(1)2, with unit cell dimensions a = 88.01 A, b = 75.86 A, c = 50.53 A and alpha = beta = gamma = 90 degrees, indicating a single molecule of 34 kDa in the asymmetric unit. The crystals grow to dimensions of 1 mm x 2 mm x 0.5 mm within two weeks in the dark and are stable in the X-ray beam for at least 40 hours. Diffraction data beyond 1.7 A resolution, observed with a synchrotron radiation source, indicate that a high resolution structure analysis is feasible. 相似文献
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E Louie M Nemeti H Torfi L B Poskanzer F R Anderson J P Johnson 《Annales de génétique》1991,34(3-4):252-255
A 15.5-year-old female was referred for primary amenorrhea and slow development of secondary sex characteristics. The karyotype revealed 45,X/46,X,+mar (75%/25%). The small marker chromosome was C-band and Q-band negative. It appeared to be primarily centromeric with some light G-band staining material on either side. Females with Y-chromosomal material are at an increased risk for gonadal neoplasia and this patient was studied further to investigate the possibility that the marker was a deleted Y chromosome. Polymerase chain reaction (PCR) analysis of this patient's DNA revealed the presence of Y-chromosomal material presumably derived from the marker chromosome. These results indicate that the PCR technique, in conjunction with cytogenetic analysis, can identify possible Y-chromosomal material. This testing provides critical information necessary for correct medical followup of Turner syndrome mosaic patients. 相似文献
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