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排序方式: 共有106条查询结果,搜索用时 390 毫秒
1.
The kinetics of release of four intracellular enzymes from different yeast cell locations using the Differential Product Release
(DPR) method has been investigated. The method uses a combination of physical, chemical and biological agents such as lytic
enzymes, an osmotic support and a spheroplast stabilizer. Using the DPR technique a wall enzyme, invertase, was released with
a very high specific activity in the first step from a breadmaking strain ofS. cerevisiae. Maximum release could be obtained in this step when the incubation time was extended from 60 min to 100 min. Two cytosol
enzymes, α-D-glucosidase and alcohol dehydrogenase were released in the second step. Fumarase was released in the third step
almost instantaneously after disruption of the mitochondria which reduces considerably, by ca. 1 hour, the total incubation
time of DPR. This paper investigates the kinetics of enzyme release during the 3 steps of DPR. 相似文献
2.
WhileEscherichia coli is common as a commensal organism in the distal ileum and colon, the presence of colonization factors (CF) on pathogenic strains ofE. coli facilitates attachment of the organism to intestinal receptor molecules in a species- and tissue-specific fashion. After the initial adherence, colonization occurs, and the involvement of additional virulence determinants leads to illness. EnterotoxigenicE. coli (ETEC) is the most extensively studied of the five categories ofE. coli that cause diarrheal disease, and has the greatest impact on health worldwide. ETEC can be isolated from domestic animals and humans. The biochemistry, genetics, epidemiology, antigenic characteristics, and cell and receptor binding properties of ETEC have been extensively described. Another major category, enteropathogenicE. coli (EPEC), has virulence mechanisms, primarily effacement and cytoskeletal rearrangement of intestinal brush borders, that are distinct from ETEC. An EPEC CF receptor has been purified and characterized as a sialidated transmembrane glycoprotein complex directly attached to actin, thereby associating CF-binding with host-cell response. Three, additional categories ofE. coli diarrheal disease, their colonization factors and their host cell receptors are discussed. It appears that biofilms exist in the intestine in a manner similar to oral bacterial biofilms, and thatE. coli is part of these biofilms as both commensals and pathogens.Abbreviations CF
colonization factor
- CFA
Colonization Factor Antigen
- CS
coli-surface-associated antigen
- EAggEC
enteroaggregativeE. coli
- ECDD
E. coli diarrheal disease
- EHEC
enterohemorrhagicE. coli
- EIEC
enteroinvasiveE. coli
- EPEC
enteropathogenicE. coli
- ETEC
enterotoxigenicE. coli
- Gal
galactose
- GalNAc
N-acetyl galactosamine
- LT
heat-labile toxin
- NeuAc
N-acetyl neuraminic acid
- PCF
Putative colonization factor
- RBC
red blood cells
- SLT
Shiga-like toxin
- ST
heat-stable toxin 相似文献
3.
DNA sequences were determined for three to five alleles of the bride-of-
sevenless (boss) gene in each of four species of Drosophila. The product of
boss is a transmembrane receptor for a ligand coded by the sevenless gene
that triggers differentiation of the R7 photoreceptor cell in the compound
eye. Population parameters affecting the rate and pattern of molecular
evolution of boss were estimated from the multinomial configurations of
nucleotide polymorphisms of synonymous codons. The time of divergence
between D. melanogaster and D. simulans was estimated as approximately 1
Myr, that between D. teissieri and D. yakuba as approximately 0.75 Myr, and
that between the two pairs of sibling species as approximately 2 Myr. (The
boss genes themselves have estimated divergence times approximately 50%
greater than the species divergence times.) The effective size of the
species was estimated as approximately 5 x 10(6), and the average mutation
rate was estimated as 1-2 x 10(-9)/nucleotide/generation. The ratio of
amino acid polymorphisms within species to fixed differences between
species suggests that approximately 25% of all possible single-step amino
acid replacements in the boss gene product may be selectively neutral or
nearly neutral. The data also imply that random genetic drift has been
responsible for virtually all of the observed differences in the portion of
the boss gene analyzed among the four species.
相似文献
4.
Evolutionary origin of human and primate malarias: evidence from the circumsporozoite protein gene 总被引:8,自引:1,他引:7
We have analyzed the conserved regions of the gene coding for the
circumsporozoite protein (CSP) in 12 species of Plasmodium, the malaria
parasite. The closest evolutionary relative of P. falciparum, the agent of
malignant human malaria, is P. reichenowi, a chimpanzee parasite. This is
consistent with the hypothesis that P. falciparum is an ancient human
parasite, associated with humans since the divergence of the hominids from
their closest hominoid relatives. Three other human Plasmodium species are
each genetically indistinguishable from species parasitic to nonhuman
primates; that is, for the DNA sequences included in our analysis, the
differences between species are not greater than the differences between
strains of the human species. The human P. malariae is indistinguishable
from P. brasilianum, and P. vivax is indistinguishable from P. simium; P.
brasilianum and P. simium are parasitic to New World monkeys. The human P.
vivax-like is indistinguishable from P. simiovale, a parasite of Old World
macaques. We conjecture that P. malariae, P. vivax, and P. vivax-like are
evolutionarily recent human parasites, the first two at least acquired only
within the last several thousand years, and perhaps within the last few
hundred years, after the expansion of human populations in South America
following the European colonizations. We estimate the rate of evolution of
the conserved regions of the CSP gene as 2.46 x 10(-9) per site per year.
The divergence between the P. falciparum and P. reichenowi lineages is
accordingly dated 8.9 Myr ago. The divergence between the three lineages
leading to the human parasites is very ancient, about 100 Myr old between
P. malariae and P. vivax (and P. vivax-like) and about 165 Myr old between
P. falciparum and the other two.
相似文献
5.
T Sasaki N F Kassell D M Turner J C Torner H C Coester 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1984,177(3):422-427
The pharmacological properties of naloxone on vascular smooth muscle in vitro were examined using canine mesenteric arterial segments. Naloxone exerted two different effects on the artery: (A) naloxone at a high concentration (3 X 10(-4) M) produced a nonspecific vasodilation; and (B) naloxone at lower concentrations (3 X 10(-7), 3 X 10(-6), and 3 X 10(-5) M) augmented the vasoconstrictor effects of epinephrine and norepinephrine without altering KCl- or serotonin-induced constriction. Naloxone's augmenting effect on epinephrine-induced constriction was dose dependent. Even when the arterial strips were incubated in low calcium (0.8 mM) or calcium free Kreb's solution, naloxone (3 X 10(-5) M) still augmented epinephrine-induced constriction. With respect to naloxone's effect on another alpha-adrenoreceptor agonist, naloxone (3 X 10(-5) M) failed to alter phenylephrine-induced constriction. Naloxone's augmenting effect on norepinephrine-induced constriction was abolished when the specimens were incubated with 10(-5) M normetanephrine, while naloxone (3 X 10(-5) M) still augmented the constriction even when the specimens were incubated with 10(-5) M cocaine. These results suggest that naloxone at lower concentrations may augment the constrictor responses to catecholamines, at least in part, by inhibiting the extraneuronal uptake of those catecholamines. 相似文献
6.
Oligomeric forms of the membrane-bound acetylcholine receptor disclosed upon extraction of the M(r) 43,000 nonreceptor peptide
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FJ Barrantes 《The Journal of cell biology》1982,92(1):60-68
Oligomeric forms of the acetylcholine receptor are directly visualized by electron microscopy in receptor-rich membranes from torpedo marmorata. The receptor structures are quantitatively correlated with the molecular species so far identified only after detergent solubilization, and further related to the polypeptide composition of the membranes and changes thereof. The structural identification is made possibly by the increased fragility of the membranes after extraction of nonreceptor peptides and their subsequent disruption upon drying onto hydrophilic carbon supports. Receptor particles in native membranes depleted of nonreceptor peptides appear as single units of 7-8 nm, and double and multiple aggregates thereof. Particle doublets having a main-axis diameter of 19 +/- 3 nm predominate in these membranes. Linear aggregates of particles similar to those observed in rotary replicas of quick-frozen fresh electrolytes (Heuser, J.E. and S. R. Salpeter. 1979, J. Cell Biol. 82: 150-173) are also present in the alkaline-extracted membranes. Chemical modifications of the thiol groups shift the distribution of structural species. Dithiothreitol reduction, which renders almost exclusively the 9S, monomeric receptor form, results in the observation of the 7-8 nm particle in isolated form. The proportion of doublets increases in membranes alkylated with N-ethylmaleimide. Treatment with 5,5’-dithiobis-(nitrobenzoic acid) increases the proportion of higher oligomeric species, and particle aggregates (n=oligo) predominate. The nonreceptor v-peptide (doublet of M(r) 43,000) appears to play a role in the receptor monomer-polymer equilibria. Receptor protein and v-peptide co-aggregate upon reduction and reoxidation of native membranes. In membranes protected ab initio with N- ethylmaleimide, only the receptor appears to self-aggregate. The v-peptide cannot be extracted from these alkylated membranes, though it is easily released from normal, subsequently alkylated or reduced membranes. A stabilization of the dimeric species by the nonreceptor v-peptide is suggested by these experiments. Monospecific antibodies against the v-peptide are used in conjunction with rhodamine- labeled anti-bodies in an indirect immunoflourescence assay to map the vectorial exposure of the v-peptide. When intact membranes, v-peptide depleted and “holey” native membranes (treated with 0.3 percent saponin) are compared, maximal labeling is obtained with the latter type of membranes, suggesting a predominantly cytoplasmic exposure of the antigenic determinants of the v-peptide in the membrane. The influence of the v-peptide in the thiol-dependent interconversions of the receptor protein and the putative topography of the peptide are analyzed in the light of the present results. 相似文献
7.
Naima Lajud Rubén Gonzalez-Zapien Angélica Roque Eréndira Tinajero Juan José Valdez Carmen Clapp Luz Torner 《Hormones and behavior》2013
Tight regulation of hormone and neurochemical milieu during developmental periods is critical for adequate physiological functions. For instance, activation of peptide systems during early life stress induces morphological changes in the brain resulting in depression and anxiety disorders. Prolactin (PRL) exerts different actions within the brain; it regulates neurogenesis and modulates neuroendocrine functions in the adult. However, PRL effects during early postnatal life are hardly known. Therefore, we examined whether neonatal administration of PRL influences cell survival in the hippocampal dentate gyrus (DG) and in the olfactory bulb (OB) and whether such influence results in behavioral consequences in adulthood. PRL-treated rat pups (13 mg/kg; PND1 to PND14), injected with BrdU at postnatal day 5 (PND5), showed a decrease in the density of DG BrdU/DCX and BrdU/NeuN-positive cells that survive at PND15. Similarly, PRL treatment decreased the density of BrdU + cells in the OB compared with VEH. Fluorojade B analysis showed no significant changes in the amount of cell death in the DG between the groups. Postnatal PRL administration induced a passive coping strategy in the forced swimming test in male and female adult rats when compared with control and vehicle groups. Corticosterone endogenous levels at PND12 were not affected by PRL or VEH treatment. Altogether, these results suggest that opposed to its effects in the adult, postnatal PRL treatment affects neurogenesis and results in psychopathology later in life. High PRL levels, as observed in neonates under several pathological states, might contribute to detrimental effects on the developing brain. 相似文献
8.
Carlos Torner Luis Sánchez-Hurtado Raúl Aguilar-Roblero 《Biological Rhythm Research》2013,44(5):538-545
In spite of the clear evidences for the blockade of dopaminergic D2 receptors as the mechanism of action for haloperidol-induced catalepsy, the contribution of pharmacokinetic and pharmacodynamic aspects on the diurnal modulation of haloperidol-induced catalepsy is controversial. We studied the diurnal variations of striatal dopamine receptors and its relation with catalepsy diurnal variations. The [3 H]-spiperone binding to dopamine receptors had a clear rhythm with a peak at 00:00 to 03:00 h, and a trough at 12:00 to 18:00 h. Haloperidol-produced catalepsy measured with the four-cork test, also showed a clear rhythm, with a peak at 00:00 h and trough at 9:00 h. The dose-response curves at peak and trough of catalepsy had the same ED 50 (0.12 mg), with time-related changes in the maximal effect. Similar diurnal variations between catalepsy and dopamine receptor binding, indicate a relevant role of temporal pharmacodynamics of haloperidol on the modulation of its behavioral effects. 相似文献
9.
Tomek W Melo Sterza FA Kubelka M Wollenhaupt K Torner H Anger M Kanitz W 《Biology of reproduction》2002,66(5):1274-1282
Meiotic maturation of mammalian oocytes (transition from prophase I to metaphase II) is accompanied by complex changes in the protein phosphorylation pattern. At least two major protein kinases are involved in these events; namely, cdc2 kinase and mitogen-activated protein (MAP) kinase, because the inhibition of these kinases arrest mammalian oocytes in the germinal vesicle (GV) stage. We show that during meiotic maturation of bovine oocytes, the translation initiation factor, eIF4E (the cap binding protein), gradually becomes phosphorylated. This substantial phosphorylation begins at the time of germinal vesicle breakdown (GVBD) and continues to the metaphase II stage. The onset of eIF4E phosphorylation occurs in parallel with a significant increase in overall protein synthesis. However, although eIF4E is nearly fully phosphorylated in metaphase II oocytes, protein synthesis reaches only basal levels at this stage, similar to that of prophase I oocytes, in which the factor remains unphosphorylated. We present evidence that a specific repressor of eIF4E, the binding protein 4E-BP1, is present and could be involved in preventing eIF4E function in metaphase II stage oocytes. Recently, two protein kinases, called Mnk1 and Mnk2, have been identified in somatic cells as eIF4E kinases, both of which are substrates of MAP kinase in vivo. In bovine oocytes, a specific inhibitor of cdk kinases, butyrolactone I, arrests oocytes in GV stage and prevents activation of both cdc2 and MAP kinase. Under these conditions, the phosphorylation of eIF4E is also blocked, and its function in initiation of translation is impaired. In contrast, PD 098059, a specific inhibitor of the MAP kinase activation pathway, which inhibits the MAP kinase kinase, called MEK function, leads only to a postponed GVBD, and a delay in MAP kinase and eIF4E phosphorylation. These results indicate that in bovine oocytes, 1) MAP kinase activation is only partially dependent on MEK kinase, 2) MAP kinase is involved in eIF4E phosphorylation, and 3) the abundance of fully phosphorylated eIF4E does not necessarily directly stimulate protein synthesis. A possible MEK kinase-independent pathway of MAP kinase phosphorylation and the role of 4E-BP1 in repressing translation in metaphase II oocytes are discussed. 相似文献
10.
Martha L. Carvour Jerald P. Harms Charles F. Lynch Randall R. Mayer Jeffery L. Meier Dawei Liu James C. Torner 《PloS one》2015,10(6)