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1.
The cat hindlimb contains several long, biarticular strap muscles composed of parallel muscle fascicles that attach to short tendons. Three of these muscles--sartorius, tenuissimus, and semitendinosus--were studied by dissecting individual gold-stained fibers and determining the surface distribution of acetylcholinesterase-stained end-plate zones. In each muscle, fascicles were composed of muscle fibers that ran only part of the fascicle length and tapered to end as fine strands that interdigitated with other tapering fibers within the muscle mass. Most muscle fibers measured 2-3 cm in length. Fascicles of muscle fibers were crossed by short transverse bands of endplates (1 mm wide by 1-5 mm long) that were spaced at fairly regular intervals from the origin to the insertion of the muscle. The endplate pattern suggested that the fiber fascicles were organized into multiple longitudinal strips. In the sartorius, the temporospatial distribution of electromyographic (EMG) activity evoked by stimulating fine, longitudinal branches of the parent nerve confirmed that each strip was selectively innervated by a small subset of the motor axons. These axons appeared to distribute their endings throughout the entire length of the fascicles, providing for synchronous activation of their in-series fibers. 相似文献
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Using a modified postmodern perspective, Canada's policy of multiculturalism and the emphasis upon ‘unity within diversity’ are related to the theme of globalization and the development of ‘a new world order’. It is argued that Canada is not unique in its efforts to come to terms with the contradictions and conflicts generated by postindustrialism and the realignment of superpowers. Questions of identity, collective self‐determination and the problematic relation between universalism and particularism, in relation to sovereignty, legitimacy, human rights and participation are explored. 相似文献
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Melanoma growth stimulatory activity (MGSA) was originally described as an endogenous growth factor for human melanoma cells. To test the hypothesis that an MGSA autocrine loop is responsible for the partial freedom from growth control observed in nevocytes and melanoma cells, MGSA growth response and MGSA mRNA/protein levels were examined in these cells compared with normal melanocytes. As a single agent, or in combination with other factors, MGSA stimulated the growth of normal human epidermal melanocytes as well as other growth promoters for melanocytes. Nevocytes were not as responsive to exogenous MGSA as melanocytes. MGSA mRNA was minimal or not detected in cultured normal melanocytes, although the protein was present when the cells were cultured in the presence of serum/growth factors and absent when serum/growth factors were omitted. In contrast, MGSA mRNA was constitutively expressed in the absence of exogenous growth factors in cultures established from benign intradermal and dysplastic nevi and melanoma lesions in different stages of tumor progression. Nevus cultures contained immunoreactive MGSA protein in the presence of serum but were negative or only faintly positive in the absence of serum. Melanoma cell lines were positive for MGSA protein in both the presence and the absence of serum. Thus, continued expression of both MGSA mRNA and MGSA protein in the absence of exogenous hormones or serum factors may correlate with partial freedom from growth control exhibited by malignant melanocytes. 相似文献
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During a study of the effects of high concentrations of NaCl, NaNO3 and KC1 on the production of lysine bySaccharomyces cerevisiae during the fermentation of glucose (Richmond 1980) it was learned that amounts of salt greater than 0.6 M in the microbiological assay sample could change the apparent concentration of lysine in the sample. This could be corrected by adding to the lysine assay broth sufficient salt to match the concentration in the sample tube and then developing a revised standard curve. The additional salt, in turn, required that the microbiological assay time be lengthened. 相似文献
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The effects of sodium bicarbonate concentration, population density, and temperature on the maintenance of an outdoor monoculture of the cyanobacterium Spirulina platensis were studied. A clear response by Spirulina to the concentration of bicarbonate was evident, with 0.2M bicarbonate representing the lowest concentration in which a monoculture could be maintained. When the temperatures fell during the winter period to some 20-25 degrees C below the optimum for Spirulina, Chlorella sp. gradually increased and became the dominant species in the culture. Raising the temperature by covering the pond with transparent polyethylene resulted in a sharp decline in the population of Chlorella, and a gradual resumption of species dominance by Spirulina. In winter, there was an inverse relationship in the pond between the population density of Spirulina and the extent of contamination by Chlorella sp.; but no such effect was observed under field conditions at temperatures higher than 25 degrees C. 相似文献
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Substrate Effect on 2,3-Butylene Glycol Production by Rhizopus nigricans and Penicillium expansum 总被引:1,自引:1,他引:0 下载免费PDF全文
Rhizopus nigricans and Penicillium expansum produced 2,3-butylene glycol which accumulated in natural and artificial media with time. Mycelial mats of P. expansum decreased the quantity of a diacetyl substrate and converted part of this substrate into acetylmethylcarbinol (AMC) and 2,3-butylene glycol. Mycelial mats of P. expansum also decreased AMC substrate with the formation of 2,3-butylene glycol. 2,3-Butylene glycol decreased slightly during incubation with the fungal mat. The formation of AMC was suppressed significantly by cysteine and ascorbic acid. 相似文献
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M. H. Richmond 《The Biochemical journal》1965,94(3):584-593
1. Three variants of staphylococcal exopenicillinase (types A, B and C) can be distinguished on chemical, enzymological and immunological grounds. 2. Enzyme type A has a higher specific activity than that of type B, but has a similar combination affinity with anti-(exopenicillinase type A) serum. 3. Enzyme types A and C have a similar specific activity, but enzyme type C has a lower combination affinity for anti-(exopenicillinase type A) serum than has enzyme type A. 4. The sedimentation coefficients and amino acid analyses of the three enzyme types are similar. 5. All three enzyme types have small but significant differences in kinetics of action when hydrolysing benzylpenicillin, methicillin, cloxacillin and cephalosporin C. 6. Peptide maps, obtained from enzyme types A and C after digestion with trypsin, show that these two variants probably differ in the nature of only a very few amino acid residues. 7. Enzyme type B seems to be confined to staphylococci that are members of staphylococcal phage group II. Enzyme types A and C are produced by staphylococci that are members either of phage group I or III, but never group II. 8. The low specific enzyme activity and affinity of enzyme type B towards all penicillins tested suggest that this enzyme type has a lower `efficiency' in hydrolysing penicillin and therefore in protecting bacteria from the action of penicillin. This could account for the low incidence among `hospital staphylococci' of penicillin-resistant staphylococci that are members of phage group II. 相似文献