刺激中缝背核压抑大鼠小脑浦肯野细胞对苔状和爬行纤维传入的反应

本文在麻醉并制动的大鼠上观察了中缝背核(DR)条件刺激对由苔状和爬行纤维传入引起的小脑浦肯野细胞(PC)诱发反应的影响。主要结果有:(1)刺激大脑皮层感觉运动区可以引起苔状和爬行纤维向对侧小脑皮层第Ⅵ和Ⅶ小叶的传入,因而在该小叶上记录到 PC 的诱发简单锋电位(SS)和复杂锋电位(CS)反应,潜伏期分别是8—25和12—30ms。(2)以不影响PC 自发 SS 和 CS 活动的阈下强度刺激 DR,可显著地压抑 PC 对于刺激感觉运动皮层引起的苔状和爬行纤维兴奋所产生的诱发 SS 和 CS 反应,这种压抑作用可持续数百毫秒。(3)DR条件刺激对 PC 的诱发 SS 和 CS 反应的压抑作用可以被静脉注射5-HT 受体阻断剂羟甲丙基甲基麦角酰胺所减弱或阻断。上述结果表明 DR 的5-HT 能纤维传入可以降低苔状和爬行纤维对 PC 的突触作用效力,抑或降低 PC 对突触传入的反应敏感性,提示中缝-小脑5-HT,能纤维传入系统参与了小脑某些重要的神经活动过程。     

GABA对大鼠下丘脑正中隆起LHRH释放调节的研究

本研究应用大鼠下丘脑正中隆起(ME),观察 γ-氨基丁酸(GABA)和去甲肾上腺素(NA)对下丘脑促黄体生成激素释放激素(LHRH)神经元末梢分泌作用的影响。结果发现:GABA(10~(-6)mol/L)可显著促进 ME 的 LHRH 和 NA 的释放,即 LHRH 释放量由27.3±2.5pg/100ul 增加至150.4±27.9pg/100μl;NA 释放量由50.9±4.2pg/100μl 增加至105.5±19.1pg/100ul,两者与对照组相比有显著差异(P<0.01)。GABA 这些作用可被受体拮抗剂荷包牡丹碱(Bicuculline)所翻转。当荷包牡丹碱和 GABA(10~(-6)mol/L)同时存在于 ME 的培灌液中,LHRH 的分泌量下降为18.2±1.9pg/100μl,而 NA 分泌量下降为43.9±3.4pg/100μl。在内源性 NA 被利血平耗竭时,LHRH 的释放量仅增加26.5%,而 GABA 能使正常大鼠 LHRH 释放量增加451.9%。本研究提示:GABA 可促进下丘脑 ME 释放 LHRH,这一作用可能通过 NA 中介。     

无眼金线鲃及其性状演化

无眼金线鲃Sinocyclocheilus anophthalmus是继我国个旧盲条鳅、无眼平鳅、裸腹盲鲃之后发现的第四种盲鱼。与近似种小孔金线鲃相比,该新种侧线鳞较少。由于它长期生活在黑暗的石灰岩溶洞之中,引起某些性状的适应性变异:眼睛消失;体无色素;鳞片退化,感觉器官特别发达。形态比较结果表明,无眼金线鲃是类似小孔金线鲃的祖先进入地下伏流后,适应黑暗环境而形成的一个种,为本属鱼类进化过程中的一个特化分支。     

A single wheatgrass chromosome reduces the concentration of barley yellow dwarf virus in wheat

Seedlings of a series of addition or substitution lines of wheat containing different Thinopyrum intermedium chromosomes were inoculated with the PAV and RPV serotypes of barley yellow dwarf virus (BYDV). Reduced virus titres in infected plants were ascribed to a single pair of homoeologous group 7 chromosomes from Th. intermedium in the disomic addition lines L1 and TAF 2. The group 7 chromosome is associated with red pigmentation of coleoptiles, which was also observed in two lines ditelosomic for the α arm of the chromosome. However, when infected with the PAV serotype of BYDV, the ditelosomic lines had normal virus titres and it is concluded that potential determinants of BYDV resistance are located on the β arm of the Group 7 chromosome.     

Primary sequence mapping of human apolipoprotein B-100 epitopes. Comparisons of trypsin accessibility and immunoreactivity and implication for apoB conformation

Differential trypsin-accessibility and monoclonal antibodies (Mabs) to human apolipoprotein (apo) B-100 are both important tools for probing apoB structure and conformation on low-density lipoproteins (LDL). In this study, we have mapped greater than 80% of the C-terminal region (720 residues) of LDL apoB-100 using trypsin digestion. Our results extend our previous data [Yang et al. (1986) Nature (Lond.) 323, 738-742] confirming that the C-terminal region of about 420 residues of apoB-100 is largely inaccessible to trypsin, whereas the part just preceding this region has interspersed trypsin-accessible and inaccessible peptides. We have determined the amino acid sequence of specific apoB-100 peptides containing epitopes recognized by four separate Mabs: two epitopes have been mapped to within 20 residues, one has been mapped to 36 residues, and the last to 80 residues. We used polyclonal antisera to identify 16 overlapping clones of varying lengths of apoB-100 cDNAs extending from the C-terminus of apoB-100 cloned in the expression vector, lambda gt11. These clones were then tested against individual Mabs. By nucleotide sequence analysis of overlapping clones that show differential reactivities to different Mabs, we have mapped the individual epitopes of each Mab to within about 50-150 amino acid residues predicted from the DNA sequences. Confirmation and further fine mapping were accomplished by competition for LDL binding using partially purified fusion proteins and chemically synthesized oligopeptides. Two epitopes (Mabs 7 and 22) were mapped to the C-terminal 20 amino acids of apoB-100, one (Mab 16) to residues 4154-4189, and another (Mab 20) to residues 3926-4005. Mab 16 precipitates more than 80% of LDL particles. Mab 20 precipitates only denatured apoB but not native LDL apoB [Milne et al. (1987) Mol. Immunol. 24, 435]. Mabs 7 and 22 are unique in that they precipitate LDL apoB modified by storage much better than freshly isolated LDL-apoB. Although epitope expression and trypsin-accessibility represent two useful probes for the study of protein conformation, there was no obvious correlation between these two parameters when applied to LDL apoB for the antibodies we have examined.     

Identification of the products and nucleotide sequences of two regulatory genes involved in the exogenous induction of phosphoglycerate transport in Salmonella typhimurium.

We describe the determination of the nucleotide sequence of two genes (pgtB and pgtC) contained within the 3.4-kilobase DNA segment sandwiched between the transporter gene, pgtP, and the regulatory gene, pgtA. These two genes are involved in the regulation of expression of phosphoglycerate transport in Salmonella typhimurium. The sequence indicates the presence of two large open reading frames, potentially coding for two polypeptides of 397 and 593 amino acid residues. The two gene products were identified by using the bacteriophage T7 RNA polymerase-T7 promoter coupled system of Tabor and Richardson, and the observed apparent mass of 45 and 69 kilodaltons correlated well with the respective open reading frames. The cellular location of these two polypeptides was directly determined, and the polypeptides were found to be associated with the membrane. Although overall these polypeptides appear to be hydrophilic, there is one hydrophobic transmembrane segment in the smaller polypeptide and four such segments in the larger polypeptide which can account for their association with the membrane. In the accompanying paper, we present genetic evidence that pgtB and pgtC genes are involved in the induction of the pgtP expression by modulating derepressor activity.     

Protonmotive Q cycle pathway of electron transfer and energy transduction in the three-subunit ubiquinol-cytochrome c oxidoreductase complex of Paracoccus denitrificans

Ubiquinol-cytochrome c oxidoreductase (cytochrome bc1) complex from Paracoccus denitrificans consists of only three polypeptide subunits (Yang, X., and Trumpower, B. L. (1986) J. Biol. Chem. 261, 12282-12289), whereas the analogous complexes of eukaryotic mitochondria consist of nine or more polypeptides (Schagger, H., Link, T. A., Engel, W. D., and von Jagow, G. (1986) Methods Enzymol. 126, 224-237). Using the purified three-subunit Paracoccus complex we have tested whether this simple cytochrome bc1 complex has the same electron transfer pathway and proton translocation activity as the bc1 complexes of mitochondria. Under presteady state conditions, the effects of inhibitors on reduction of cytochromes b and c1 by quinol and oxidant-induced reduction of cytochrome b indicate a cyclic electron transfer pathway and two routes of cytochrome b reduction in the three-subunit Paracoccus cytochrome bc1 complex. A novel method was developed to incorporate the cytochrome bc1 complex into liposomes with the detergent dodecyl maltoside. The enzyme reconstituted into liposomes translocated protons with an H+/2e value of 3.9. Carbonyl cyanide m-chlorophenylhydrazone eliminated proton translocation, while permitting the scalar release of protons from quinol, and thus reduced the H+/2e ratio to 2. These values agree with the predicted stoichiometries for proton translocation by a protonmotive Q cycle pathway. No inhibition of proton translocation by N',N'-dicyclohexylcarbodiimide was detected when the Paracoccus cytochrome bc1 complex was incubated with N',N'-dicyclohexylcarbodiimide before or after reconstitution into liposomes. Electron transfer in the three-subunit complex thus appears to occur by a protonmotive Q cycle pathway identical to that in mitochondrial cytochrome bc1 complexes. Only three polypeptides, cytochromes b, c1, and the Rieske iron-sulfur protein, are required for respiration and energy transduction in the cytochrome bc1 complex. The function of the supernumerary polypeptides in mitochondrial bc1 complexes is thus unclear.     

Dephosphorylation of the beta 2-adrenergic receptor and rhodopsin by latent phosphatase 2

Recent evidence suggests that the function of receptors coupled to guanine nucleotide regulatory proteins may be controlled by highly specific protein kinases, e.g. rhodopsin kinase and the beta-adrenergic receptor kinase. In order to investigate the nature of the phosphatases which might be involved in controlling the state of receptor phosphorylation we studied the ability of four highly purified well characterized protein phosphatases to dephosphorylate preparations of rhodopsin or beta 2-adrenergic receptor which had been highly phosphorylated by beta-adrenergic receptor kinase. These included: type 1 phosphatase, calcineurin phosphatase, type 2A phosphatase, and the high molecular weight latent phosphatase 2. Under conditions in which all the phosphatases could dephosphorylate such common substrates as [32P]phosphorylase a and [32P]myelin basic protein at similar rates only the latent phosphatase 2 was active on the phosphorylated receptors. Moreover, a latent phosphatase activity was found predominantly in a sequestered membrane fraction of frog erythrocytes. This parallels the distribution of a beta-adrenergic receptor phosphatase activity recently described in these cells (Sibley, D. R., Strasser, R. H., Benovic, J. L., Daniel, K., and Lefkowitz, R. J. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 9408-9412). These data suggest a potential role for the latent phosphatase 2 as a specific receptor phosphatase.     

Insulin induces activation and translocation of protein kinase FA (a multifunctional protein phosphatase activator) in human platelet

Protein kinase FA (an activator of the ATP.Mg-dependent multifunctional protein phosphatase) has been identified in both cytosol and plasma membrane isolated from human platelets. The FA activity in the cytosol is active whereas the FA activity in the membrane is inactive. Quantitative analysis further indicates that approximately 90% of total FA is present in the membrane whereas only 10% of FA is localized in the cytosol, suggesting that the inactive membrane-associated FA might be regulated. This notion has subsequently been demonstrated that exposure of platelets to physiological concentrations of insulin for only 1 min resulted in an increase in cytosolic FA activity to about 300% of control values in the absence of insulin and in a corresponding decrease in FA activity in the membrane. It is concluded that the molecular basis for insulin action on cellular metabolism may partly be mediated through the activation and translocation of protein kinase FA in the membrane. It is suggested that redistribution of protein kinase FA may represent a transmembrane signal of insulin.