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61.
Ioannis Dragatsis Christine Zioudrou Kyriaki Gerozissis 《Cellular and molecular neurobiology》1995,15(4):389-400
Summary 1. Inin vitro studies with adult male rats we have recently shown that the delta-opioid agonist DTLET inhibits the release of the Gonadotropin-Releasing Hormone (GnRH) from hypothalamic fragments containing the arcuate nucleus and the median eminence. This effect is receptor mediated and eicosanoid dependent (Gerozissiset al., 1993).2. In the present study we report that the delta-opioid antagonists with negative intrinsic activity, Diallyl-G and ICI 174864, applied under the same experimental conditions (30 min static incubations at 37°C, in a potassium rich milieu), in the absence of the agonist DTLET, also exert a similar to the agonist inhibitory effect on the release of GnRH.3. The dose-dependent inhibitory effect of Diallyl-G on GnRH release is reversed by increasing concentrations of DTLET. The mu and delta opioid antagonist, naloxone is without effect in the absence of DTLET. However, naloxone acts as an antagonist on the Diallyl-G-induced inhibition of GnRH release.4. Diallyl-G also inhibits the release of prostaglandin E2 (PGE2). In the presence of indomethacin or nordihydroguaiaretic acid, Diallyl-G is ineffective to further inhibit the release of GnRH. These latter observations taken together with the results of eicosanoid estimation suggest that PGE2 but not leukotrienes participate in the agonist-independent effects of Diallyl-G on GnRH release.5. Therefore these results support the hypothesis that delta-opioid antagonists with negative intrinsic activity exert agonist-independent biological responses similar to those of the agonists. 相似文献
62.
Fabrice Cornille Loïc Martin Christine Lenoir Didier Cussac Bernard P. Roques Marie-Claude Fournié-Zaluski 《Letters in Peptide Science》1997,4(4-6):207-212
The light chain of tetanus neurotoxin (TeNT L chain)has been shown to be endowed with zinc endopeptidaseactivity, selectively directed towards theGln76–Phe77 bond of synaptobrevin, avesicle-associated membrane protein criticallyinvolved in neuroexocytosis. In previous reports,truncations at the NH2- and COOH-terminus ofsynaptobrevin have shown that the sequence 39–88 ofsynaptobrevin is the minimum substrate of TeNT,suggesting either the requirement of a well-definedthree-dimensional structure of synaptobrevin or a rolein the mechanism of substrate hydrolysis for residuesdistal from the cleavage site. In this study, theaddition of NH2- and COOH-terminal peptides ofsynaptobrevin, S 27–55 (S1) and S 82–93(S2), to the synaptobrevin fragment S 56–81allowed the cleavage of this latter peptide by TeNT tooccur. This appears to result from an activationprocess mediated by the simultaneous binding ofS1 and S2 with complementary sites presenton TeNT as shown by surface plasmon resonanceexperiments. All these results favor anexosite-controlled hydrolysis of synaptobrevin by TeNTprobably involving a conformational change of thetoxin. This could account for the high degree ofsubstrate specificity of TeNT and, probably, botulinumneurotoxins. 相似文献
63.
Florine Cavelier Christine Enjalbal Jérome Santolini Francis Haraux Claude Sigalat Jean Verducci François André 《Letters in Peptide Science》1997,4(4-6):283-288
Tentoxin[cyclo-(MeAla1-Leu2-MePhe3-Gly4] is a metabolite isolated from a phytopathogenic fungusAlternaria alternata, which induces chlorosis of many plants. This potentialnatural herbicide binds specifically to the soluble part CF1of the chloroplastic coupling factor, which is a proton ATP-synthase. Theeffect of the toxin is concentration dependent: at low concentration it is apowerful inhibitor, while at higher concentration, it stimulates the enzyme.We synthesized tentoxin and we designed new analogues in order to vary thehydrophobicity on the side chain and to study the structure activityrelationships. Comparative activities suggest that it is possible toseparate inhibitory and activating effects using tentoxin analogues, showingsome evidence for the existence of two binding sites with different affinityconstant. 相似文献
64.
65.
Christine K. Wagner Joan I. Morrell 《The Journal of steroid biochemistry and molecular biology》1997,61(3-6):307-314
Aromatase, the enzyme responsible for the conversion of testosterone to estradiol, is found in the rat brain and is present in regions of the preoptic area, hypothalamus, and limbic system. Gonadal steroid hormones regulate aromatase activity levels in many brain regions, but not all. Using in situ hybridization, we examined the distribution of aromatase mRNA in the adult male forebrain, as well as the levels of aromatase mRNA in the brains of males and females, and the regulation by gonadal steroid hormones. In the adult male, many heavily labelled cells were found in the encapsulated bed nucleus of the stria terminalis (BNST), the medial preoptic nucleus (MPN), the ventro-medial nucleus (VMN), the medial amygdala (mAMY) and the cortical amygdala (CoAMY). The regional distribution of aromatase mRNA was similar in males and females, but males tended to have a greater number of aromatase mRNA-expressing cells in each region compared to females. Aromatase mRNA levels in the BNST, MPN, VMN and mAMY tended to be lower in castrated males than in intact males, whereas aromatase mRNA levels were unaltered by castration in the CoAMY. Further analysis of individual cells expressing aromatase mRNA suggests that aromatase mRNA may be regulated by steroid hormones differentially in specific populations of cells in regions where enzyme activity levels are steroid-hormone-dependent. 相似文献
66.
Christian Biémont Cristina Vieira Christine Hoogland Géraldine Cizeron Catherine Lœvenbruck Claude Arnault Jean-Pierre Carante 《Genetica》1997,100(1-3):161-166
To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed
the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of
insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects
of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is
strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes,
which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted
by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural
populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra,
Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2
× 10-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations.
The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements
in this species could result from a low transposition rate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
67.
Active Site Mutations in Yeast Protein Disulfide Isomerase Cause Dithiothreitol Sensitivity and a Reduced Rate of Protein Folding in the Endoplasmic Reticulum 总被引:7,自引:0,他引:7 下载免费PDF全文
Aspects of protein disulfide isomerase (PDI) function have been studied in yeast in vivo. PDI contains two thioredoxin-like domains, a and a′, each of which contains an active-site CXXC motif. The relative importance of the two domains was analyzed by rendering each one inactive by mutation to SGAS. Such mutations had no significant effect on growth. The domains however, were not equivalent since the rate of folding of carboxypeptidase Y (CPY) in vivo was reduced by inactivation of the a domain but not the a′ domain. To investigate the relevance of PDI redox potential, the G and H positions of each CGHC active site were randomly mutagenized. The resulting mutant PDIs were ranked by their growth phenotype on medium containing increasing concentrations of DTT. The rate of CPY folding in the mutants showed the same ranking as the DTT sensitivity, suggesting that the oxidative power of PDI is an important factor in folding in vivo. Mutants with a PDI that cannot perform oxidation reactions on its own (CGHS) had a strongly reduced growth rate. The growth rates, however, did not correlate with CPY folding, suggesting that the protein(s) required for optimal growth are dependent on PDI for oxidation. pdi1-deleted strains overexpressing the yeast PDI homologue EUG1 are viable. Exchanging the wild-type Eug1p C(L/I)HS active site sequences for C(L/I)HC increased the growth rate significantly, however, further highlighting the importance of the oxidizing function for optimal growth. 相似文献
68.
Instantaneous scan sampling for mean distance and synchronous action patterns and all-occurrence sampling for unison call, dance, strut, and hoover-up behaviors were conducted for five potential whooping crane pairs at Patuxent Environmental Science Center, Laurel, Maryland. Dance, strut, and hoover-up differed among pairs, as did total frequency of social behaviors. It was unclear whether or not total frequency of social behaviors during pair formation can be used as an index for potential breeding success. The relative importance of different action patterns should be used as indices of pair compatibility in captive whooping cranes. © 1995 Wiley-Liss, Inc. 相似文献
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