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排序方式: 共有159条查询结果,搜索用时 15 毫秒
1.
2.
A Vandermeers M C Vandermeers-Piret J Rathe J P Dehaye J Winand J Christophe 《Peptides》1984,5(2):359-365
Rat pancreatic acini were preincubated with 0.4 mM 32Pi for 45 min at 37 degrees C, then exposed for 15 min to VIP, secretin or CCK-8. The incubation was terminated with a stop solution and a fraction rich in mitochondria and zymogen granules was separated from a microsome-rich fraction by differential centrifugation. After heating in the presence of SDS, beta-mercaptoethanol was added and the pattern of equivalent amounts of 32P-labelled proteins was examined by autoradiography of SDS-PAGE gels. VIP, secretin, and CCK-8 stimulated the phosphorylation of a Mr=33 K microsomal protein and that of two proteins of Mr=21 K and Mr=25 K mostly present in a fraction rich in mitochondria and zymogen granules. Stimulations were dose-dependent, the highest stimulant concentrations tested allowing 2- to 3-fold increases of phosphorylation over basal. When 1 nM CCK-8 was used simultaneously with 1 microM VIP, the cyclic AMP levels attained and the pattern of protein phosphorylation were similar to those obtained with VIP alone, and there was a potentiation of amylase secretion; when a supra-maximal 0.1 microM CCK-8 concentration was added, the VIP-induced elevation in cyclic AMP levels and the phosphorylation of the Mr=21 K and Mr=25 K proteins were partially antagonized, and no potentiation any more of secretion occurred. To conclude the in vitro phosphorylation of three particulate proteins (Mr=33 K, 25 K, and 21 K) was similarly increased in rat pancreatic acini in response to secretin and VIP (acting through cyclic AMP) and to CCK-8 (acting mostly through Ca2+). 相似文献
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N. ChaÏb E. Kabré M. Métioui E. Alzola H. Amsallem A. Marino A. Moran J.P. Dehaye 《Peptides》1998,19(10):1759-1770
A cellular suspension from rat submandibular glands was prepared with collagenase. The intracellular pH (pHi) was estimated with 2′,7′-bis-(2-carboxy-ethyl)-5(6)-carboxyfluorescein (BCECF). After exposure to NH4Cl, the pHi transiently increased (diffusion of NH3) and then dropped (influx of NH4+). Isoproterenol increased 2.5-fold the rate of NH4+ influx; bumetanide, an inhibitor of the Na+-K+-2Cl−-cotransporter blocked the response to isoproterenol, confirming that the beta-adrenergic agonist stimulated the cotransporter. Forskolin (1 μmol/L) mimicked the response to isoproterenol. VIP (1 nmol/L-1 μmol/L) also increased the activity of the cotransporter. Cyclic AMP rather than calcium was the mediator of this activation since 1) carbachol which increased the [Ca2+]i fivefold increased the uptake of NH4+ by only 50%; 2) only high concentrations of VIP significantly increased the [Ca2+]i; 3) incubation in the presence of EGTA had no effect on the response to VIP; 4) low concentrations (nmol/L) of the neuropeptide increased the intracellular level of cAMP; and 5) the stimulation of the cotransporter by VIP, forskolin, and isoproterenol was inhibited by H8, an inhibitor of cAMP-dependent protein kinase. It is concluded that the Na+-K+-2Cl−-cotransporter of rat submandibular glands is activated by isoproterenol, forskolin, and neuropeptides of the VIP family by a mechanism involving cAMP-dependent processes. The activation of the cotransporter by VIP could partly explain the potentiating effect of VIP on the response to sialagogues like substance P or muscarinic agonists.1 相似文献
5.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
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van Dijken JP Bauer J Brambilla L Duboc P Francois JM Gancedo C Giuseppin ML Heijnen JJ Hoare M Lange HC Madden EA Niederberger P Nielsen J Parrou JL Petit T Porro D Reuss M van Riel N Rizzi M Steensma HY Verrips CT Vindeløv J Pronk JT 《Enzyme and microbial technology》2000,26(9-10):706-714
To select a Saccharomyces cerevisiae reference strain amenable to experimental techniques used in (molecular) genetic, physiological and biochemical engineering research, a variety of properties were studied in four diploid, prototrophic laboratory strains. The following parameters were investigated: 1) maximum specific growth rate in shake-flask cultures; 2) biomass yields on glucose during growth on defined media in batch cultures and steady-state chemostat cultures under controlled conditions with respect to pH and dissolved oxygen concentration; 3) the critical specific growth rate above which aerobic fermentation becomes apparent in glucose-limited accelerostat cultures; 4) sporulation and mating efficiency; and 5) transformation efficiency via the lithium-acetate, bicine, and electroporation methods. On the basis of physiological as well as genetic properties, strains from the CEN.PK family were selected as a platform for cell-factory research on the stoichiometry and kinetics of growth and product formation. 相似文献
8.
Lindström Irene Bontell Neil Hall Kevin E Ashelford JP Dubey Jon P Boyle Johan Lindh Judith E Smith 《Genome biology》2009,10(5):R53-17
Background
Toxoplasma gondii is a zoonotic parasite of global importance. In common with many protozoan parasites it has the capacity for sexual recombination, but current evidence suggests this is rarely employed. The global population structure is dominated by a small number of clonal genotypes, which exhibit biallelic variation and limited intralineage divergence. Little is known of the genotypes present in Africa despite the importance of AIDS-associated toxoplasmosis. 相似文献9.
Luaine Bandounas Nick JP Wierckx Johannes H de Winde Harald J Ruijssenaars 《BMC biotechnology》2011,11(1):1-11
Background
The number of biotransformations that use nicotinamide recycling systems is exponentially growing. For this reason one of the current challenges in biocatalysis is to develop and optimize more simple and efficient cofactor recycling systems. One promising approach to regenerate NAD+ pools is the use of NADH-oxidases that reduce oxygen to hydrogen peroxide while oxidizing NADH to NAD+. This class of enzymes may be applied to asymmetric reduction of prochiral substrates in order to obtain enantiopure compounds.Results
The NADH-oxidase (NOX) presented here is a flavoenzyme which needs exogenous FAD or FMN to reach its maximum velocity. Interestingly, this enzyme is 6-fold hyperactivated by incubation at high temperatures (80°C) under limiting concentrations of flavin cofactor, a change that remains stable even at low temperatures (37°C). The hyperactivated form presented a high specific activity (37.5 U/mg) at low temperatures despite isolation from a thermophile source. Immobilization of NOX onto agarose activated with glyoxyl groups yielded the most stable enzyme preparation (6-fold more stable than the hyperactivated soluble enzyme). The immobilized derivative was able to be reactivated under physiological conditions after inactivation by high solvent concentrations. The inactivation/reactivation cycle could be repeated at least three times, recovering full NOX activity in all cases after the reactivation step. This immobilized catalyst is presented as a recycling partner for a thermophile alcohol dehydrogenase in order to perform the kinetic resolution secondary alcohols.Conclusion
We have designed, developed and characterized a heterogeneous and robust biocatalyst which has been used as recycling partner in the kinetic resolution of rac-1-phenylethanol. The high stability along with its capability to be reactivated makes this biocatalyst highly re-useable for cofactor recycling in redox biotransformations. 相似文献10.
Margaret?O?Nwagwu Helen?Baines Jeffrey?B?Kerr Francis?JP?EblingEmail author 《Reproductive biology and endocrinology : RB&E》2005,3(1):48