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1.
A number of different membrane associated isoforms of the neural cell adhesion molecule (N-CAM) have previously been identified. Here the structure of a novel secreted isoform of N-CAM is established by analysis of a cDNA corresponding to an N-CAM mRNA from human skeletal muscle. The mRNA incorporates a novel sequence block into the extracellular domain, which introduces an in-frame stop codon and thus prematurely terminates the coding sequence, generating a truncated N-CAM polypeptide. Analysis of genomic clones indicates that the inserted sequence is present as a discrete exon within the human N-CAM gene, and Northern analysis shows it to be associated specifically with a 5.2 kb mRNA species from skeletal muscle and brain. Stable transfectants expressing the secreted isoform accumulate it in the cytoplasm and release it to the culture medium. In contrast, cells transfected with cDNA encoding lipid-tailed N-CAM express it predominantly at the cell surface. The existence of a secreted isoform may further expand the spectrum of N-CAM function beyond its known involvement in intercellular adhesion to extracellular matrix interactions. 相似文献
2.
The metabolism of pregnenolone in subcellular fractions of the testes of the macaque (Macaca fascicularis) has been studied using capillary gas chromatography to characterize and quantify the metabolites, after their conversion into the O-methyloxime and/or trimethylsilyl ether derivatives. The microsomal incubations yielded the greatest quantities of metabolites, with lesser amounts in the mitochondrial fraction. The cytosolic fraction contained no significant quantity of metabolites after incubation, except for 5alpha-androst-16-en-3 beta-ol. This, and other odorous androst-16-enes, found in the microsomal fraction, are of particular interest in the context of animal communication because of their possible pheromonal role. Pregnenolone was converted into androst-5-ene-3 beta,17 beta-diol, androst-4-ene-3,17-dione and testosterone, suggesting that both classical pathways for testosterone synthesis were operating. Testosterone was further converted into 5 alpha-reduced androstanediols, especially in the microsomal fraction. 相似文献
3.
We have isolated the delta-globin gene of the New-World spider monkey,
Ateles geoffroyi, and compared its nucleotide sequence with those of other
primate delta- and beta-globin genes. Among primate delta-globin genes, the
rate of nonsynonymous substitutions is much less than the rate of
synonymous substitutions. This suggests that primate delta- globin genes
may remain under evolutionary conservation, perhaps because hemoglobin A2
has an as yet unknown physiological importance.
相似文献
4.
5.
Biochemical pathways in prokaryotes can be traced backward through evolutionary time 总被引:10,自引:0,他引:10
For the first time, a credible prokaryotic phylogenetic tree is being
assembled by Woese and others using quantitative sequence analysis of
oligonucleotides in the highly conservative rRNA. This provides an
evolutionary scale against which the evolutionary steps that led to the
arrangement and regulation of contemporary biochemical pathways can be
measured. This paper presents an emerging evolutionary picture of aromatic
amino acid biosynthesis within a large superfamily assemblage of
prokaryotes that is sufficiently developed to illustrate a new perspective
that will be applicable to many other biochemical pathways.
相似文献
6.
7.
A method for the determination of desferrioxamine-available iron in tissue fractions is described which involves incubation with desferrioxamine, extraction of desferrioxamine and its iron-bound form, ferrioxamine, and quantitation of these two forms of the drug by reversed-phase hplc analysis. Chelatable iron levels in the 1-10µMolar region could be accurately and reproducibly measured using this technique.
The desferrioxamine-available iron levels in both the cortex and medulla of rabbit kidneys were significantly elevated (up to 2-fold) after the organs had been subjected to 2 hours warm ischaemia or 24 hours cold storage at 0°C In hypertonic citrate solution. There was no change in the total iron content of the tissues under these circumstances and thus a redistribution of intracellular iron to more available pools had presumably taken place as a result of ischaemia. This redistribution of iron may be an important factor in the initiation of peroxidative damage to cell membranes upon reperfusion of the organ with oxygen. 相似文献
The desferrioxamine-available iron levels in both the cortex and medulla of rabbit kidneys were significantly elevated (up to 2-fold) after the organs had been subjected to 2 hours warm ischaemia or 24 hours cold storage at 0°C In hypertonic citrate solution. There was no change in the total iron content of the tissues under these circumstances and thus a redistribution of intracellular iron to more available pools had presumably taken place as a result of ischaemia. This redistribution of iron may be an important factor in the initiation of peroxidative damage to cell membranes upon reperfusion of the organ with oxygen. 相似文献
8.
Neuronal process outgrowth of human sensory neurons on monolayers of cells transfected with cDNAs for five human N-CAM isoforms 总被引:14,自引:7,他引:7 下载免费PDF全文
P Doherty C H Barton G Dickson P Seaton L H Rowett S E Moore H J Gower F S Walsh 《The Journal of cell biology》1989,109(2):789-798
Full length cDNAs for a variety of human N-CAM isoforms have been transfected into mouse L-cells and/or 3T3 cells. Three independent clones of each cell line that were shown to express human N-CAM were tested for their ability to support the morphological differentiation of sensory neurons. The cell surface expression of N-CAM isoforms, linked to the membrane directly by an integral transmembrane spanning domain or indirectly via covalent attachment to a glycosyl-phosphatidylinositol moiety, were consistently found to be associated with a significant increase in the morphological differentiation of both human and rat dorsal root ganglion neurons. Modification of the extracellular structure of both classes of N-CAM, consequent to the expression of a glycosylated 37-amino acid sequence normally found expressed exclusively in muscle N-CAM isoforms did not obviously affect the ability of transfected cells to support increased neuronal differentiation. 3T3 cells that were transfected with a full length cDNA encoding a secreted N-CAM isoform, and that have previously been shown to secrete N-CAM into the growth media rather than link it to the membrane did not significantly differ from control cells in their ability to support neuronal differentiation. These data provide direct evidence for both transmembrane and lipid-linked N-CAM isoforms being components of the regulatory machinery that determines neuronal morphology and process outgrowth. 相似文献
9.
In Drosophila pseudoobscura, the amylase (Amy) multigene family is
contained within a series of inversions, or gene arrangements, on the third
chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL)
inversions are central to the phylogeny of arrangements, and have clusters
of other arrangements derived from them. The gene arrangements belonging to
each of these three clusters have a characteristic number of Amy genes,
ranging from three in ST to two in SC to one in TL. This distribution
pattern can reflect a history of either duplications or deletions, although
the data available in the past did not permit a decision between these
alternatives. We provide unambiguous evidence that three Amy genes were
present before the divergence of the ST, SC, and TL arrangements. Thus, the
current status of the Amy multigene family is the result of deletions in
the TL and SC arrangements, which created three new pseudogenes: TL
Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences
revealed that, in the SC and ST arrangements, pseudogene evolution has been
retarded, most likely due to the homogenization effect of gene conversion.
Finally, by determining the original copy number, we have reconstructed the
evolutionary history of the Amy multigene family and linked it with the
evolution of the central gene arrangements.
相似文献
10.
William R. Gower Jr. Robert M. Risch Constantine V. Godellas Peter J. Fabri 《In vitro cellular & developmental biology. Animal》1994,30(3):151-161
Summary A new human pancreatic cancer (HPAC) cell line was established from a nude mouse xenograft (CAP) of a primary human pancreatic
ductal adenocarcinoma. In culture, HPAC cells form monolayers of morphologically heterogenous, polar epithelial cells, which
synthesize carcinoembryonic antigen, CA 19-9, CA-125, cytokeratins, antigens for DU-PAN-2, HMFG1, and AUA1, but do not express
chromogranin A or vimentin indicative of their pancreatic ductal epithelial cell character. In the presence of serum, HPAC
cell DNA synthesis was stimulated by insulin, insulin growth factor-I, epidermal growth factor, and TGF-α but inhibited
by physiologic concentrations of hydrocortisone and dexamethasone. Dose-dependent inhibition of DNA synthesis was limited
to steroids with glucocorticoid activity. The inhibitory effect of dexamethasone was abolished by the glucocorticoid antagonist
RU 38486. Binding of [3H]dexamethasone to cytosolic proteins was specific and saturable at 4° C. Scatchard analysis of binding data demonstrated
a single class of high-affinity binding sites (Kd=3.8±0.9 nM; Bmax=523±128 fmol/mg protein). Western blot analysis revealed a major protein band that migrated at a Mr of 96 kDa. Northern blot analysis identified an mRNA of approximately 7 kilobases which hybridized with a specific glucocorticoid
receptor complementary DNA probe (OB7). These findings support a role for glucocorticoids in the regulation of human malignant
pancreatic cell function. 相似文献