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31.
K C Chou 《The Biochemical journal》1983,215(3):465-469
It is demonstrated that the observed low-frequency motions with wave numbers of 22 cm-1 and 25 cm-1 for insulin and lysozyme respectively originate from the accordion-like motions of the principal helices therein. The calculated results based on such a model are in good agreement with the observed values. During calculations the role of the internal microenvironment upon the low-frequency motion is naturally revealed, so as to elucidate as well why this kind of low-frequency motion is so sensitive to the conformations of proteins observed. 相似文献
32.
The process of osmotic shock, which has been used to release degradative enzymes from Escherichia coli, can be applied successfully to other members of the Enterobacteriaceae. Cyclic phosphodiesterase (3'-nucleotidase), 5'-nucleotidase (diphosphate sugar hydrolase), acid hexose phosphatase, and acid phenyl phosphatase are released from Shigella, Enterobacter, Citrobacter, and Serratia strains. Some strains of Salmonella also release these enzymes. Members of Proteus and Providencia groups fail to release enzymes when subjected to osmotic shock and do not show a lag in regrowth, although they do release their acid-soluble nucleotide pools. In contrast to E. coli, release of enzymes from other members of the Enterobacteriaceae studied is affected by growth conditions and strain of organism. None of the organisms was as stable to osmotic shock in exponential phase of growth as was E. coli. Exponential-phase cells of Shigella, Enterobacter, and Citrobacter could be shocked only with 0.5 mm MgCl(2) to prevent irreparable damage to the cells. These observations suggest that this group of degradative enzymes is probably loosely bound to the cytoplasmic membrane through the mediation of divalent cations. 相似文献
33.
Expression of insulin-like growth factor-I and its receptor by SV40-transformed rat granulosa cells 总被引:2,自引:0,他引:2
M Zilberstein J Y Chou W L Lowe Z Shen-Orr C T Roberts D LeRoith K J Catt 《Molecular endocrinology (Baltimore, Md.)》1989,3(9):1488-1497
Cellular proliferation is a dominant aspect of ovarian follicular development in the rat, and insulin-like growth factor I (IGF-I) has been proposed as a mediator of cellular growth and differentiation in the ovary. An SV40-transformed rat granulosa cell line (RGA-41S) has been established as a model for studies on dividing cells of granulosa origin. Granulosa cells from the ovaries of immature diethylstilbestrol-treated rats were infected with the tsA255 mutant of SV40, followed by cloning in serum-free medium to select transformed cell lines which were serum independent. At the permissive temperature (33 C), RGA-41S cells exhibited a transformed phenotype and rapidly formed high density multilayers of compact cells that readily overgrew nontransformed cells. At the nonpermissive temperature (40 C) cell replication declined and division ceased after 4 days. Furthermore, at 40 C the cells grew as a monolayer and assumed a tetrahedral shape with a high cytoplasm-to-nucleus ratio, and displayed reduced ability to overgrow nontransformed cells. The transformed ovarian cells did not express detectable gonadotropin receptors and steroidogenic activity but retained their epithelial phenotype as demonstrated by cytokeratin staining of the cytoskeleton, the presence of microvilli, and the formation of tight junctions between cells. In support of the proposed autocrine-paracrine actions of IGF-I in the ovary, assay of conditioned serum-free culture medium revealed secretion of IGF-I-immunoreactive material by RGA-41S cells. HPLC-purified IGF-I immunoreactivity from these cells eluted with the same retention time as recombinant human IGF-I. When hybridized with a 32P-labeled rat IGF-I cDNA probe, poly(A)+ mRNA prepared from RGA-41S cells grown at both temperatures showed the typical three size classes of IGF-I mRNA on Northern blots (7.5, 1.7, and 0.8-1.2 kilobase kb), although the levels were somewhat higher at 33 C. The presence of IGF-I receptors in transformed cells was demonstrated by specific 125I-IGF-I binding to intact cells. Scatchard analysis indicated a single class of high affinity receptors at a density of 10(5) binding sites per cell and a dissociation constant (Kd) = 0.52 x 10(-9) M. Furthermore, hybridization of a 32P-labeled IGF-I receptor probe to Northern blots of poly(A+) RNA prepared from cells grown at 33 C and 40 C revealed an 11-kilobase rat IGF-I receptor mRNA. Physiological concentrations of IGF-I increased [3H]aminoisobutyric acid uptake by RGA-41S cells grown at either temperature, attesting to the retention of responsiveness to IGF-I in these transformed granulosa cells.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
34.
C F Yang Z C Zeng S C Chou F X Yu J D Taylor T T Tchen 《Pigment cell research / sponsored by the European Society for Pigment Cell Research and the International Pigment Cell Society》1989,2(5):408-413
We have previously shown that the dispersion and aggregation of carotenoid droplets in goldfish xanthophores are regulated, respectively, by phosphorylation and dephosphorylation of a carotenoid droplet protein p57. There is a basal level of p57 phosphorylation of p57 in unstimulated cells, which is greatly stimulated by adrenocorticotropic hormone (ACTH) or cyclic adenosine monophosphate (cAMP) acting via cAMP-dependent protein kinase. We have also observed that, in permeabilized xanthophores, pigment dispersion can be induced when cAMP is replaced by fluoride. Since p57 has multiple phosphorylation sites, there is the question of whether all p57 phosphorylation is by cAMP-dependent protein kinase or whether phosphorylation by cAMP-independent protein kinase coupled with inhibition of phosphatase activity by fluoride can replace cAMP-dependent protein kinase and that the ability of fluoride to replace cAMP for pigment dispersion in permeabilized cells is probably due to activation of adenylcyclase. We also show that ACTH causes an approximately threefold increase in the level of cAMP in these cells. 相似文献
35.
36.
C K Chou T S Su C M Chang C P Hu M Y Huang C S Suen N W Chou L P Ting 《The Journal of biological chemistry》1989,264(26):15304-15308
The human hepatoma Hep3B cells contain integrated hepatitis B viral genome and continually secret hepatitis B surface antigen (HBsAg). The production of HBsAg (but not alpha-fetoprotein) was suppressed by addition of low concentrations (0.1-1 nM) of insulin into serum-free medium. In addition, the suppression of HBsAg production by insulin was paralleled with the decrease in HBsAg mRNA abundance. Insulin also cause a rapid rate of disappearance of HBsAg mRNA (t 1/2, 2 h) in Hep3B cells. The Hep3B cells carry specific receptor with high affinity for insulin (Kd = 1.8 nM). The receptor showed an insulin-dependent protein tyrosine kinase activity. The half-maximal insulin concentration for the activation of the receptor kinase was about 5 nM. Only very high concentrations of insulin-like growth factor I and human proinsulin can compete for the insulin receptor binding and suppress HBsAg production, this suggests that insulin may act through its receptor binding to suppress HBsAg expression in human hepatoma Hep3B cells. 相似文献
37.
38.
亚洲薄荷的两个化学型 总被引:2,自引:0,他引:2
周荣汉 《植物资源与环境学报》1994,3(3):58-59
亚洲薄荷的两个化学型桂新,周荣汉(安徽中医学院中药系合肥230038)(中国药科大学植物化学分类研究室南京210038)TwochemotypesofMenthaasiaficaBoriss¥ChouGui-Xin(AnhuiCollegeofTra... 相似文献
39.
Murine monoclonal antibodies specific for conserved and non-conserved antigenic determinants of the human and murine Ku autoantigens 总被引:5,自引:0,他引:5
40.
The use of thidiazuron in tissue culture 总被引:15,自引:0,他引:15
Chin-Yi Lu 《In vitro cellular & developmental biology. Plant》1993,29(2):92-96
Summary Thidiazuron (N-phenyl-N’-1,2,3-thiadiazol-5-ylurea) was first reported to have cytokinin activity in 1982. Since then, thidiazuron has been used
successfully in vitro to induce adventitious shoot formation and to promote axillary shoot proliferation. Thidiazuron is especially
effective with recalcitrant woody species. Shoot numbers produced on medium containing thidiazuron are equivalent to or greater
than numbers initiated on medium with purine-type cytokinins. Low concentrations of thidiazuron (0.0022 to 0.088 mg/liter)
are effective for micropropagation. Prolonged exposure to thidiazuron should be avoided, as this may cause hyperhydricity,
abnormal shoot morphology, or problems in rooting.
Presented in the Session-in-Depth Novel Plant Growth Regulators at the 1992 World Congress on Cell and Tissue Culture, Washington,
D.C., June 20–25, 1992. 相似文献