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排序方式: 共有216条查询结果,搜索用时 297 毫秒
1.
2.
Abstract. Two opposite views have been proposed to explain the decline of the growth potential in cell populations with a limited life span: 1 variations in the probability of cycling and in cycling times or 2 a progressive increase in the nondividing cell fraction. Human brain-derived cells were studied with respect to their proliferative potential under the influence of different growth conditions, using haptotactic palladium islands on agarose. The results emphasize the need for cell co-operation, surface area and nutrients for cell division. These parameters also influence the final cell density. The results illustrate the multiple factors that can vary the probability of initiating the division cycle and stress the uncertainty of defining the irreversible non-dividing state. 相似文献
3.
Premjit P. Halarnkar Charles R. Heisler Gary J. Blomquist 《Archives of insect biochemistry and physiology》1987,5(3):189-199
The metabolism of succinate was examined in the housefly Musca domestica L. The labeled carbons from [2,3-14C]succinate were readily incorporated into cuticular hydrocarbon and internal lipid, whereas radioactivity from [1,4-14C]succinate was not incorporated into either fraction. Examination of the incorporation of [2,3-14C]succinate, [1-14C]acetate, and [U-14C]proline into hydrocarbon by radio-gas-liquid chromatography showed that each substrate gave a similar labeling pattern, which suggested that succinate and proline were converted to acetyl-CoA prior to incorporation into hydrocarbons. Carbon-13 nuclear magnetic resonance showed that the labeled carbons from [2,3-13C]succinate enriched carbons 1, 2, and 3 of hydrocarbons with carbon-carbon coupling showing that carbons 2 and 3 of succinate were incorporated as an intact unit. Radio-high-performance liquid chromatographic analysis of [2,3-14C]succinate metabolism by mitochondrial preparations showed that in addition to labeling fumarate, malate, and citrate, considerable radioactivity was also present in the acetate fraction. The data show that succinate was not converted to methylmalonate and did not label hydrocarbon via a methylmalonyl derivative. Malic enzyme was assayed in sonicated mitochondria prepared from the abdomens and thoraces of 1- and 4-day-old insects; higher activity was obtained with NAD+ in mitochondria prepared from thoraces, whereas NADP+ gave higher activity with abdomen preparations. These data document the metabolism of succinate to acetyl-CoA and not to a methylmalonyl unit prior to incorporation into lipid in the housefly and establish the role of the malic enzyme in this process. 相似文献
4.
Sami Ahmad Kenneth E. Kirkland Gary J. Blomquist 《Archives of insect biochemistry and physiology》1987,6(2):121-140
Direct evidence is presented for the role of a cytochrome P-450 monooxygenase (called mixed-function oxidase, or polysubstrate mono-oxygenase, PSMO) in the metabolism of the sex pheromone (Z)-9-tricosene to its corresponding epoxide and ketone in the housefly. A secondary alcohol, most likely an intermediate in the conversion of the alkene to the ketone, was also tentatively identified. The results of in vivo and in vitro experiments showed that the PSMO inhibitors, piperonyl butoxide (PB) and carbon monoxide, markedly inhibited the formation of epoxide and ketone from (9,10-3H) (Z)-9-tricosene. An examination of the relative rates of (Z)-9-tricosene metabolism showed that males exhibited a higher rate of metabolism than females with the antennae of males showing the highest activity of any tissue/organ examined. The major product from all tissues/organs was the epoxide. Data from experiments with subcellular fractions showed that the microsomal fraction had the majority of enzyme activity, which was strongly inhibited by PB and CO and required NADPH and O2 for activity. A carbon monoxide difference spectrum with reduced cytochrome showed maximal absorbance at 450 nm and allowed quantification of the cytochrome P-450 in the microsomal fraction of 0.410-nmol cytochrome P-450 mg?1 protein. Interaction of (Z)-9-tricosene with the cytochrome P-450 resulted in a type I spectrum, indicating that the pheromone binds to a hydrophobic site adjacent to the heme moiety of the oxidized cytochrome P-450. 相似文献
5.
The alpha-like globin gene cluster in rabbits contains embryonic zeta-
globin genes, an adult alpha-globin gene, and theta-globin genes of
undetermined function. The basic arrangement of genes, deduced from
analysis of cloned DNA fragments, is 5'-zeta 0-zeta 1-alpha 1-theta 1- zeta
2-zeta 3-theta 2-3'. However, the pattern of restriction fragments
containing zeta- and theta-globin genes varies among individual rabbits.
Analysis of BamHI fragments of genomic DNA from 24 New Zealand white
rabbits revealed eight different patterns of fragments containing
zeta-globin genes. The large BamHI fragments containing genes zeta 0 and
zeta 1 are polymorphic in length, whereas a 1.9-kb fragment containing the
zeta 2 gene and the 3.5-kb fragment containing the zeta 3 gene do not vary
in size. In contrast to this constancy in the size of the restriction
fragments, the copy number of the zeta 2 and zeta 3 genes does vary among
different rabbits. No length polymorphism was detected in the BamHI
fragments containing the theta-globin genes, but again the copy number
varies for restriction fragments containing the theta 2 gene. The alpha 1-
and theta 1-globin genes are located in a nonpolymorphic 7.2-kb BamHI
fragment. The combined data from hybridization with both zeta and theta
probes shows that the BamHI cleavage pattern does not vary within the
region 5'-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3', but the pattern
genomic blot-hybridization patterns for the progeny of parental rabbits
with different zeta-globin gene patterns shows that the polymorphic
patterns are inherited in a Mendelian fashion. Two different haplotypes
have been mapped based on the genomic blot-hybridization data. The
variation in the alpha-like globin gene cluster in the rabbit population
results both from differences in the copy number of the duplication block
containing the zeta-zeta-theta gene set and from the presence or absence of
polymorphic BamHI sites.
相似文献
6.
Selective partitioning of conidia of some Penicillium and Aspergillus species in aqueous two-phase systems. 总被引:2,自引:1,他引:1
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Conidia of Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger, Penicillium brevi-compactum, Penicillium frequentans, Penicillium spinulosum, and Penicillium verrucosum var. cyclopium were subjected to partition at varying pH values in an aqueous two-phase system containing charged polyethylene glycol. In the system, the partition behavior of the conidia of the Penicillium species varied when the pH was raised, while the conidia of the Aspergillus species seemed unaffected. P. brevi-compactum was separated from P. verrucosum var. cyclopium after only 10 transfers when subjected to stepwise partitioning. In the same way, 10 transfers were needed to separate P. verrucosum var. cyclopium from a mixture of conidia of three Aspergillus species. The partition behavior was influenced by the culture media used. 相似文献
7.
Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium 总被引:13,自引:9,他引:4
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Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel. 相似文献
8.
C H Blomquist N J Lindemann E Y Hakanson 《Archives of biochemistry and biophysics》1985,239(1):206-215
During storage at 4 degrees C, the 17 beta-hydroxysteroid dehydrogenase activity of human placental microsomes with estradiol-17 beta was more stable than that with testosterone. In order to evaluate the basis for this difference, kinetics with C18-, C19-, and C21- steroids as substrates and/or inhibitors was studied in conjunction with an analysis of the effects of detergents. Both 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) and 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD) activities were detected. At pH 9.0, apparent Michaelis constants were 0.8, 1.3, and 2.3 microM for estradiol-17 beta, testosterone, and 20 alpha-dihydroprogesterone, respectively, 17 beta-HSD activity with testosterone was inhibited by estradiol-17 beta, 5 alpha-dihydrotestosterone, 5 beta-dihydrotestosterone, 20 alpha-dihydroprogesterone, and progesterone. In each case 90 to 100% inhibition was observed at 50 to 200 microM steroid. Activity with 20 alpha-dihydroprogesterone was similarly sensitive to inhibition by C19-steroids. By contrast, 25 to 45% of the activity with estradiol-17 beta was not inhibited by high concentrations of C19- or C21-steroids and differed from the 17 beta-HSD activity with testosterone and the major fraction of that with estradiol-17 beta by being insensitive to solubilization by detergent. These results are consistent with an association of two dehydrogenase activities with human placental microsomes. One recognizes C18-, C19-, and C21-steroids as substrates with comparable affinities. The second appears to be highly specific for estradiol-17 beta. The former activity may account for most if not all of the oxidation-reduction at C-17 of C19-steroids and at C-20 of C21-compounds at physiological concentrations by term placental tissue. 相似文献
9.
10.
Tupa Basuroy Megan Dreier Caitlin Baum Thomas Blomquist Robert Trumbly Fabian V. Filipp Ivana L. de la Serna 《Pigment cell & melanoma research》2023,36(1):19-32
Lineage-specific differentiation programs are activated by epigenetic changes in chromatin structure. Melanin-producing melanocytes maintain a gene expression program ensuring appropriate enzymatic conversion of metabolites into the pigment, melanin, and transfer to surrounding cells. During neuroectodermal development, SMARCA4 (BRG1), the catalytic subunit of SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complexes, is essential for lineage specification. SMARCA4 is also required for development of multipotent neural crest precursors into melanoblasts, which differentiate into pigment-producing melanocytes. In addition to the catalytic domain, SMARCA4 and several SWI/SNF subunits contain bromodomains which are amenable to pharmacological inhibition. We investigated the effects of pharmacological inhibitors of SWI/SNF bromodomains on melanocyte differentiation. Strikingly, treatment of murine melanoblasts and human neonatal epidermal melanocytes with selected bromodomain inhibitors abrogated melanin synthesis and visible pigmentation. Using functional genomics, iBRD9, a small molecule selective for the bromodomain of BRD9 was found to repress pigmentation-specific gene expression. Depletion of BRD9 confirmed a requirement for expression of pigmentation genes in the differentiation program from melanoblasts into pigmented melanocytes and in melanoma cells. Chromatin immunoprecipitation assays showed that iBRD9 disrupts the occupancy of BRD9 and the catalytic subunit SMARCA4 at melanocyte-specific loci. These data indicate that BRD9 promotes melanocyte pigmentation whereas pharmacological inhibition of BRD9 is repressive. 相似文献