酪氨酸对人离体滋养层细胞孕酮与hCG分泌的影响

本文观察三种剂量(2×10~(-5)mol/L,2×10~(-4)mol/L和2×10~(-3)mol/L)的酪氮酸对离体培养的滋养层细胞孕酮及hCG分泌的影响,并对其抑制效应的机理作了初步探讨。实验结果表明,三种剂量的酪氨酸均可抑制滋养层细胞孕酮分泌(P<0.01),但是,在孕酮分泌受酪氨酸抑制的同时,未见对hCG分泌发生影响(P>0.05),进一步观察了酪氨酸对滋养层细胞3β-羟甾脱氢酶活性的影响,结果表明,酪氨酸能显著抑制3β-羟甾脱氢酶活性,提示酪氨酸对滋养层细胞孕酮生成的抑制作用与抑制3β-羟甾脱氢酶活性有关。     

Interferon inhibits the accumulation of glycerol phosphate dehydrogenase mRNA in oligodendrocytes and C6 cells

We investigated the effect of rat interferon-/ (IFN) on the expression of glycerol phosphate dehydrogenase (E.C.1.1.1.8; GPDH), in both C6 cells and pure cultures of oligodendrocytes. IFNs are naturally produced inhibitors of cell growth that can also affect differentiated cell functions. GPDH is a biochemical marker for oligodendrocytes and is known to be developmentally regulated and steroid inducible. GPDH activity is induced by hydrocortisone (HC) 3.5 fold in C6 cells and 5 fold in oligodendrocytes compared to untreated cultures. A pretreatment of these cells with 75 U/ml of rat IFN-/ resulted in an inhibition of the HC induction of GPDH enzymatic activity by 50% and 40% in C6 cells and oligodendrocytes respectively. We also found that IFN impaired the accumulation of GPDH mRNA in both cell types. These results demonstrate that IFNs are capable of modifying the cellular response to hormones in cells of neuroepithelial origin, and suggest the possibility that IFNs may be able to influence the development and function of the brain.Special issue dedicated to Dr. Paola S. Timiras     

Structure of the bovine eye lens gamma s-crystallin gene (formerly beta s)

The organization of a number of crystallin genes has already been resolved. One of the remaining genes of which the structure was hitherto unknown is the gamma s gene (formerly beta s). We determined the complete sequence of the bovine gamma s-crystallin-coding gene, apart from the middle region of the first intron. Since it contains three exons and two introns, we conclude that the former beta s, also at the gene level is gamma-crystallin-like. However, it is located on chromosome 3, in contrast to other gamma genes which occur in tandem on the human chromosome 2.     

胄蝗属一新种及其染色体组型与带型分析(直翅目:蝗总科)

胄蝗属(Stolzia Willemse)的种类,已知分布于菲律宾、印度尼西亚、马来西亚及我国等地区。在我国已知仅一种,即海南胄蝗Stolzia hainanensis(Tinkham).作者等于1985年9月,在海南省尖峰岭地区采集时,采得胄蝗属一新种,我们同时对该种蝗虫的染色体组型和带型进行了观察,现记述如下。 模式标本保存于陕西师范大学生物系蝗虫研究室。 尖峰胄蝗Stolzia jianfengensis新种 雄性:体中小型,密具皱纹和刻点。头顶近平,狭三角形,突出于触角基节之前,眼间距极狭,其最狭处狭于触角基节的宽度;颜面侧观倾斜,在触角基部之间的下方略凹曲,颜     

Detection and identification of FaeC as a minor component of K88 fibriilae of Escherichia coli

A tribrid gene containing ompF, faeC, and lacZ sequences was constructed by subcloning a large central segment of the K88ab gene encoding the fibrillar subunit-like protein FaeC into the open reading frame expression vector pORF2. The resulting tribrid protein was isolated and used to raise antibodies against the FaeC protein. These antibodies were then used for the detection and subcellular localization of the FaeC protein in Escherichia coli harbouring the K88ab-encoding plasmid pFM205 or mutant derivatives. Immunoblotting of subcellular fractions and of purified fibrillae, and agglutination experiments using whole cells revealed that the FaeC protein is present in the periplasm and as a minor component in the K88ab fibrillae. FaeC was also detected in purified K88ac and K88ad fibrillae. Immunoelectron microscopy confirmed the presence of FaeC in K88ab fibrillae, particularly at the tips of the longer fibrillae.     

Mechanism of L-glutamate transport in membrane vesicles from Bacillus stearothermophilus.

In the presence of electrochemical energy, several branched-chain neutral and acidic amino acids were found to accumulate in membrane vesicles of Bacillus stearothermophilus. The membrane vesicles contained a stereo-specific transport system for the acidic amino acids L-glutamate and L-aspartate, which could not translocate their respective amines, L-glutamine and L-asparagine. The transport system was thermostable (Ti = 70 degrees C) and showed highest activities at elevated temperatures (60 to 65 degrees C). The membrane potential or pH gradient could act as the driving force for L-glutamate uptake, which indicated that the transport process of L-glutamate is electrogenic and that protons are involved in the translocation process. The electrogenic character implies that the anionic L-glutamate is cotransported with at least two monovalent cations. To determine the mechanistic stoichiometry of L-glutamate transport and the nature of the cotranslocated cations, the relationship between the components of the proton motive force and the chemical gradient of L-glutamate was investigated at different external pH values in the absence and presence of ionophores. In the presence of either a membrane potential or a pH gradient, the chemical gradient of L-glutamate was equivalent to that specific gradient at different pH values. These results cannot be explained by cotransport of L-glutamate with two protons, assuming thermodynamic equilibrium between the driving force for uptake and the chemical gradient of the substrate. To determine the character of the cotranslocated cations, L-glutamate uptake was monitored with artificial gradients. It was established that either the membrane potential, pH gradient, or chemical gradient of sodium ions could act as the driving force for L-glutamate uptake, which indicated that L-glutamate most likely is cotranslocated in symport with one proton and on sodium ion.     

The primary structure of human secretogranin II, a widespread tyrosine-sulfated secretory granule protein that exhibits low pH- and calcium-induced aggregation

Secretogranin II (previously also called chromogranin C) is a tyrosine-sulfated secretory protein found in secretory granules in a wide variety of endocrine cells and neurons. Here, we have determined the primary structure of human secretogranin II from a full length cDNA clone and have investigated its properties, predicted from the sequence, by studying the behavior of purified secretogranin II under conditions characteristic of the milieu of secretory granules. Analysis of a 2.35-kilobase cDNA clone isolated from a human pituitary library and identified as secretogranin II by various criteria showed that human presecretogranin II is a 617-residue polypeptide containing an NH2-terminal located signal peptide. Secretogranin II lacks the disulfide-bonded loop structure near the NH2 terminus which is conserved in chromogranin A and chromogranin B (secretogranin I), two other widespread constituents of neuroendocrine secretory granules, but like the latter two proteins contains (i) an -E-N/S-L-X-A/D-X-D/E-X-E-L- motif and (ii) multiple potential dibasic cleavage sites for the generation of smaller, perhaps biologically active peptides. Another structural feature that secretogranin II shares with chromogranin A and chromogranin B (secretogranin I) is the abundance of acidic residues all along the polypeptide chain whose negative charge must somehow be neutralized to allow condensation and packaging of the protein into secretory granules. Experiments with purified secretogranin II showed that in the presence of 10 mM calcium at pH 5.2, conditions characteristic of the milieu of neuroendocrine secretory granules, this protein formed aggregates. Immunoglobulin G, a secretory protein that in vivo is not packaged into secretory granules, did not form aggregates under these in vitro conditions and was excluded from the secretogranin II aggregates. Very little aggregation of secretogranin II was observed in the absence of calcium at pH 5.2 or in the presence of calcium at neutral pH. In vivo, ammonium chloride, which is known to neutralize the pH of acidic intracellular compartments, inhibited the packaging of newly synthesized secretogranin II into secretory granules. Our results suggest that the low pH- and calcium-induced aggregation of secretogranin II may be important for the organization of the secretory granule matrix and raise the possibility that aggregation of secretogranin II may be involved in its sorting to secretory granules.     

The acquisition of increased insulin-responsive hexose transport in 3T3-L1 adipocytes correlates with expression of a novel transporter gene

The expression of two genes encoding facilitated glucose transporter proteins was studied during the differentiation of the 3T3-L1 fibroblastic cell line into adipocytes. The mRNA encoding the widely expressed HepG2/brain glucose transporter (GTI) is detectable in fibroblasts and its abundance remains unchanged during differentiation. On the other hand, the mRNA encoding a glucose transporter protein (GTIII) localized exclusively to muscle and adipose tissue is undetectable in fibroblasts but present in adipocytes. GTIII mRNA is first expressed three days after differentiation of 3T3-L1 cells has begun. Similarly, it is not until 3 days following the initiation of differentiation that GTIII protein can be detected, as assayed either by Western immunoblot or indirect immunofluorescence. The latter technique localizes GTIII predominantly to the perinuclear region of the adipocyte. The appearance of GTIII in developing fat cells correlates temporally with the acquisition of an increased stimulation of hexose uptake by maximal concentrations of insulin. These data support the concept that the marked increase in hexose transport in adipocytes in response to insulin is dependent on the expression in these cells of a specific, hormone-regulatable transport protein.     

Decreased thermal denaturation temperature of osteogenesis imperfecta mutant collagen is independent of post-translational overmodifications of lysine and hydroxylysine

Fibroblasts from many patients with osteogenesis imperfecta (OI) synthesize and secrete Type I collagen which is both overmodified and exhibits a decreased thermal denaturation temperature. We have examined the relationship between overmodification and decreased melting temperature in several favorable OI mutants by selectively inhibiting lysyl hydroxylase activity with the drug Minoxidil and comparing the melting profiles of the resultant undermodified collagen with untreated control. Minoxidil treatment causes an appreciable decrease in hydroxylysine with compensatory increases in lysine content, and the delayed sodium dodecyl sulfate-polyacrylamide gel electrophoretic mobility of the overmodified collagen chains becomes normal. However, the decreased melting temperature was unchanged from untreated OI control. When unhydroxylated collagen produced by normal control and OI fibroblasts incubated with alpha,alpha'-dipyridyl was examined, mutant OI molecules melted at a lower temperature than control. These data indicate that the decreased thermal denaturation temperature of OI mutant collagen is independent of post-translational overmodification of lysine or hydroxylysine. Presumably, substitutions for glycine in the Gly-X-Y structural motif distort the helix and produce lower melting temperatures by presently unknown mechanisms.