共查询到20条相似文献,搜索用时 15 毫秒
1.
Molecular Pharmacology of Organic Cation Transporters in Kidney 总被引:5,自引:0,他引:5
2.
3.
The permeation properties of KAT1, an inward rectifying potassium channel from plant cells, were investigated with different
ions in the external medium. With either K+, NH+
4 or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH+
4 but not to the slightly bigger, methylated analogue of NH+
4, MA. Substituting NH+
4 for K+ shifted the voltage dependency of channel activation further negative and hastened activation kinetics. This suggests that
channel operation depends on the transported substrate. In mixed solution (50 mm K+, 50 mm MA) MA inhibited K+ current in a voltage-independent manner. The maximum block did not exceed 50% of the K+ current. In contrast, when NH+
4 was the permeant ion (50 mm NH+
4, 50 mm MA) MA caused a voltage-dependent, slowly developing open channel block, achieving complete inhibition at very negative voltages.
The latter block could be partially overcome by the addition of K+ in the external solution. The data support a model in which ions, after entering the channel pore, compete with different
affinities for binding sites on their permeation pathway.
Received: 6 October 1997/Revised: 28 January 1998 相似文献
4.
Willett CS 《Journal of molecular evolution》2000,50(2):175-183
Convergence in amino acid sequences between proteins can be strong evidence for selection. Here, I look for evidence of convergence
in the amino acid sequences of pheromone binding protein (PBP) in response to convergence in pheromones. PBPs are involved
in sex pheromone reception by the antennae of male moths. In this role PBPs may selectively bind pheromone components and
experience convergent selection in response to convergence in pheromone components. However, examination of the PBPs of the
taxa that have converged upon the use of (E)- or (Z)-11-tetradecenyl acetate as their major pheromone component reveals little evidence for convergence in the PBPs identified
from these taxa. A few sites show a pattern consistent with convergence or parallelism; however, it cannot be ruled out that
these sites share the ancestral state. Two of these sites fall within the proposed binding region of PBPs. These results suggest
that PBPs either have not converged in sequence or have converged at very few sites in response to convergence on the same
pheromone component.
Received: 29 July 1999 / Accepted: 8 November 1999 相似文献
5.
Jak (Janus kinase) is a nonreceptor tyrosine kinase, which plays important roles in signal transduction pathways. The unique
feature of Jak is that, in addition to a fully functional tyrosine kinase domain (JH1), Jak possesses a pseudokinase domain
(JH2). Although JH2 lost its catalytic function, experimental evidence has shown that this domain may have acquired some new
but unknown functions. This apparent functional divergence after the (internal) domain duplication may result in dramatic
changes of selective constraints at some sites. We conducted a data analysis to test this hypothesis. Our result shows that
shifted selective constraints (or shifted evolutionary rates) between the JH1 and the JH2 domains are statistically significant.
Predicted amino acid sites by posterior analysis can be classified into two groups: very conserved in JH1 but highly variable
in JH2, and vice versa. Moreover, we have studied the evolutionary pattern of four tissue-specific genes, Jak1, Jak2, Jak3, and Tyk2, which were
generated in the early stages of vertebrates. We found that after the (first) gene duplication, site-specific rate shifts
between Jak2/Jak3 and Jak1/Tyk are significant, presumably as a consequence of functional divergence among these genes. The
implication of our study for functional genomics is discussed. 相似文献
6.
The potency and specificity of a novel organic I
h
current blocker DK-AH 268 (DK, Boehringer) was studied in cultured rat trigeminal ganglion neurons using whole-cell patch-clamp
recording techniques. In neurons current-clamped at the resting potential, the application of 10 μm DK caused a slight hyperpolarization of the membrane potential and a small increase in the threshold for action potential
discharge without any major change in the shape of the action potential. In voltage-clamped neurons, DK caused a reduction
of a hyperpolarization-activated current. Current subtraction protocols revealed that the time-dependent, hyperpolarization-activated
currents blocked by 10 μm DK or external Cs+ (3 mm) had virtually identical activation properties, suggesting that DK and Cs+ caused blockade of the same current, namely I
h
. The block of I
h
by DK was dose-dependent. At the intermediate and higher concentrations of DK (10 and 100 μm) a decrease in specificity was observed so that time-independent, inwardly rectifying and noninactivating, voltage-gated
outward potassium currents were also reduced by DK but to a much lesser extent than the time-dependent, hyperpolarization-activated
currents. Blockade of the time-dependent, hyperpolarization-activated currents by DK appeared to be use-dependent since it
required hyperpolarization for the effect to take place. Relief of DK block was also aided by membrane hyperpolarization.
Since both the time-dependent current blocked by DK and the Cs+-sensitive time-dependent current behaved as I
h
, we conclude that 10 μm DK can preferentially reduce I
h
without a major effect on other potassium currents. Thus, DK may be a useful agent in the investigation of the function of
I
h
in neurons.
Received: 3 March 1995/Revised: 8 July 1997 相似文献
7.
Juan Ausiö Manfred L. J. Van Veghel Raquel Gomez Daniel Barreda 《Journal of molecular evolution》1997,45(1):91-96
We have isolated and characterized for the first time, the SNBPs from an organism (Neofibularia nolitangere) of the phylum Porifera (Sponges). We have shown that these proteins consist of histones which, as expected, exhibit an amino
acid composition very similar to that of other eukaryotic histones. The finding of histones in the sperm of these primitive
organisms provides support to the notion that histones (SNBPs of the histone, H, type) were the proteins present at the onset
of SNBP evolution. In contrast, a discrete number of alternative SNBP types (protamine-like, PL; protamine, P, types) seem
to have appeared later on in the course of evolution and are found in both protostomes and deuterostomes, most likely as a
result of processes of parallel evolution.
Received: 5 March 1997 / Accepted: 6 March 1997 相似文献
8.
Evolution of Human Polyomavirus JC: Implications for the Population History of Humans 总被引:4,自引:0,他引:4
Sugimoto C Hasegawa M Kato A Zheng HY Ebihara H Taguchi F Kitamura T Yogo Y 《Journal of molecular evolution》2002,54(3):285-297
The polyomavirus JC virus (JCV), the etiological agent of progressive multifocal leukoencephalopathy, is ubiquitous in the
human population, infecting children asymptomatically, then persisting in the kidney. The main mode of transmission of JCV
is from parents to children through long-term cohabitation. Twelve JCV subtypes that occupy unique domains in Europe, Africa,
and Asia have been identified. Here, we attempted to elucidate the evolutionary relationships among JCV strains worldwide
using the whole-genome approach with which a highly reliable phylogeny of JCV strains can be reconstructed. Sixty-five complete
JCV DNA sequences, derived from various geographical regions and belonging to 11 of the 12 known subtypes, were subjected
to phylogenetic analysis using three independent methods: the neighbor-joining, maximum parsimony, and maximum likelihood
methods. The trees obtained with these methods consistently indicated that ancestral JCVs were divided into three superclusters,
designated as Types A, B, and C. A split in Type A generated two subtypes, EU-a and -b, mainly containing European and Mediterranean
strains. The first split in Type B generated Af2 (the major African subtype). Subsequent splits in Type B generated B1-c (a
minor European subtype) and all seven Asian subtypes (B1-a, -b, -d, B2, MY, CY, and SC). Type C generated a single subtype
(Af1), consisting of strains derived from western Africa. While the present findings provided a basis on which to classify
JCV into types or subtypes, they have several implications for the divergence and migration of human populations.
Received: 4 April 2001 / Accepted: 31 July 2001 相似文献
9.
Blue light effects on the acclimation of energy partitioningcharacteristics in PSII and CO2 assimilation capacity in spinachto high growth irradiance were investigated. Plants were grownhydroponically in different light treatments that were a combinationof two light qualities and two irradiances, i.e. white lightand blue-deficient light at photosynthetic photon flux densities(PPFDs) of 100 and 500 µmol m–2 s–1. The CO2assimilation rate, the quantum efficiency of PSII (PSII) andthermal dissipation activity / in young, fully expanded leaves were measured under 1,600 µmol m–2 s–1white light. The CO2 assimilation rate and PSII were higher,while / was lower in plants grown under high irradiancethan in plants grown under low irradiance. These responses wereobserved irrespective of the presence or absence of blue lightduring growth. The extent of the increase in the CO2 assimilationrate and PSII and the decrease in / by high growth irradiance was smaller under blue light-deficient conditions. These resultsindicate that blue light helps to boost the acclimation responsesof energy partitioning in PSII and CO2 assimilation to highirradiance. Similarly, leaf N, Cyt f and Chl contents per unitleaf area increased by high growth irradiance, and the extentof the increment in leaf N, Cyt f and Chl was smaller underblue light-deficient conditions. Regression analysis showedthat the differences in energy partitioning in PSII and CO2assimilation between plants grown under high white light andhigh blue-deficient light were closely related to the differencein leaf N. 相似文献
10.
Romeu Cardoso Guimarães Edward N. Trifonov Jaime Lagunez-Otero 《Journal of molecular evolution》1997,45(3):271-277
Linguistic similarities and dissimilarities between 5 S rRNA sequences allowed taxonomical separation of species and classes.
Comparisons with the molecule from mammals distinguished fungi and plants from protists and animals. Similarities to mammalians
progressively increased from protists to invertebrates and to somatic-type molecules of the vertebrates lineage. In this,
deviations were detected in avian, oocyte type, and pseudogene sequences. Among bacteria, actinobacteria were most similar
to the mammalians, which could be related to the high frequency of associations among members of these groups. Some archaebacterial
species most similar to the mammalians belonged to the Thermoproteales and Halobacteria groups. Comparisons with the soybean
mitochondrial molecule revealed high internal homogeneity among plant mitochondria. The eubacterial groups most similar to
it were Thermus and Rhodobacteria γ-1 and α-2. Other procedures have already indicated similarities of Rhodobacteria α to
mitochondria but the linguistic similarities were on the average higher with the first two groups.
Received: 5 August 1996 / Accepted: 9 April 1997 相似文献
11.
We characterized a full-length gene encoding wild silkmoth Antheraea pernyi fibroin (Ap-fibroin) to clarify the conformation of repetitive sequences. The gene consisted of a first exon encoding 14
amino acid residues, a short intron (120 bp), and a long second exon encoding 2,625 amino acid residues. Three amino acids,
alanine, glycine, and serine, amounted to 81% of the Ap-fibroin sequence. The Ap-fibroin, except for 155 residues of the amino
terminus, was composed of 80 tandemly arranged polyalanine-containing units (motifs). A motif was a doublet of a polyalanine
block (PAB) and a nonpolyalanine block (NPAB). Seventy-eight of the 80 motifs were classified into four types based on differences
in the NPAB sequences. Although respective motifs were significantly conserved, many rearrangements were observed within the
second exon, i.e., the triplication of a 558-bp-long sequence and other duplication events of shorter sequences. Chi-like
sequences, GCTGGAG, might contribute to the rearrangement within the gene as described in human minisatellite loci, because
they were found at specific sites of NPAB-encoding sequences in three of four types of motifs. The present results support
the idea that the Ap-fibroin gene is unstable like minisatellite sequences and that the evolution of this gene is strongly
associated with its instability.
Received: 18 February 2000 / Accepted: 30 June 2000 相似文献
12.
The uptake of l-leucine by trout red blood cells and peripheral lymphocytes has been analyzed. The present study shows two functionally different
Na+-independent systems for apolar branched-chain amino acids. They are designated as L systems because they share some properties
with the mammalian L system. The carrier present in red blood cells has low K
m
values, is trans-stimulable and not stereospecific for leucine uptake; on the other hand, the system present in lymphocytes is stereospecific
for leucine uptake and trans-inhibitable. Both carriers are pH sensitive in a similar fashion at low pHs, but there are important differences at higher
pH values (above neutrality). These properties are compared with these of the asc systems previously reported in these cells.
Received: 2 June 1995/Revised: 7 March 1996 相似文献
13.
Richard Lawn Lazlo Patthy Graziano Pesole Cecilia Saccone 《Journal of molecular evolution》1997,44(2):234-236
Human apolipoprotein(a), a risk factor for heart disease, has over 80% sequence identity to plasminogen. Plasminogen contains
five distinct kringle domains plus a catalytic protease subunit. Human apo(a) consists of multiple copies (the number varies
in individuals) of a domain resembling kringle 4, a single copy of a domain resembling kringle 5, and a protease-like domain.
The recently cloned hedgehog version of apolipoprotein(a), which contains 31 nearly identical copies of plasminogen kringle
3 and lacks a protease domain, has prompted us to investigate the evolutionary history of the apolipoprotein (a) gene in mammals.
Our analysis supports the nonfunctionality of the human apolipoprotein(a) protease domain, and a single (or multiple) duplication
of plasminogen gene before mammal radiation, which originated apolipoprotein(a) in mammals.
Received: 26 February 1996 / Accepted: 6 August 1996 相似文献
14.
C.L. Bashford G.M. Alder L.G. Fulford Y.E. Korchev E. Kovacs A. MacKinnon C. Pederzolli C.A. Pasternak 《The Journal of membrane biology》1996,150(1):37-45
Nonelectrolytes such as polyethylene glycols (PEG) and dextrans (i) promote the association of S. aureus α-toxin with liposomes (shown by Coomassie staining) and (ii) enhance the rate and extent of calcein leakage from calcein-loaded
liposomes; such leakage is inhibited by H+, Zn2+ and Ca2+ to the same extent as that of nonPEG-treated liposomes. Incubation of liposomes treated with α-toxin in the presence of PEG
with the hydrophobic photo-affinity probe 3-(trifluoromethyl)-3-m-[125I]iodophenyl)diazirine(125I-TID) labels monomeric and—predominantly—hexameric forms of liposome-associated α-toxin; in the absence of PEG little labeling
is apparent. At high concentrations of H+ and Zn2+ but not of Ca2+—all of which inhibit calcein leakage—the distribution of label between hexamer and monomer is perturbed in favor of the latter.
In α-toxin-treated planar lipid bilayers from which excess toxin has been washed away, PEGs and dextrans strongly promote
the appearance of ion-conducting pores. The properties of such pores are similar in most regards to pores induced in the absence
of nonelectrolytes; they differ only in being more sensitive to ``closure' by voltage (as are pores induced in cells). In
both systems, the stimulation by nonelectrolytes increases with concentration and with molecular mass up to a maximum around
2,000 Da. We conclude (i) that most of the α toxin that becomes associated with liposome or planar lipid bilayers does not
form active pores and (ii) that the properties of α-toxin-induced pores in lipid bilayers can be modulated to resemble those
in cells.
Received: 2 October 1995/Revised: 3 November 1995 相似文献
15.
The effect of l-arginine on transepithelial ion transport was examined in cultured M-1 mouse renal cortical collecting duct (CCD) cells using
continuous short circuit current (I
SC
) measurements in HCO3
−/CO2 buffered solution. Steady state I
SC
averaged 73.8 ± 3.2 μA/cm2 (n= 126) and was reduced by 94 ± 0.6% (n= 16) by the apical addition of 100 μm amiloride. This confirms that the predominant electrogenic ion transport in M-1 cells is Na+ absorption via the epithelial sodium channel (ENaC). Experiments using the cationic amino acid l-lysine (radiolabeled) as a stable arginine analogue show that the combined activity of an apical system y+ and a basal amino acid transport system y+L are responsible for most cationic amino acid transport across M-1 cells. Together they generate net absorptive cationic
amino acid flux. Application of l-arginine (10 mm) either apically or basolaterally induced a transient peak increase in I
SC
averaging 36.6 ± 5.4 μA/cm2 (n= 19) and 32.0 ± 7.2 μA/cm2 (n= 8), respectively. The response was preserved in the absence of bath Cl− (n= 4), but was abolished either in the absence of apical Na+ (n= 4) or by apical addition of 100 μm amiloride (n= 6). l-lysine, which cannot serve as a precursor of NO, caused a response similar to that of l-arginine (n= 4); neither L-NMMA (100 μm; n= 3) nor L-NAME (1 mm; n= 4) (both NO-synthase inhibitors) affected the I
SC
response to l-arginine. The effects of arginine or lysine were replicated by alkalinization that mimicked the transient alkalinization
of the bath solution upon addition of these amino acids. We conclude that in M-1 cells l-arginine stimulates Na+ absorption via a pH-dependent, but NO-independent mechanism. The observed net cationic amino acid absorption will counteract
passive cationic amino acid leak into the CCD in the presence of electrogenic Na+ transport, consistent with reports of stimulated expression of Na+ and cationic amino acid transporters by aldosterone.
Received: 11 September 2000/Revised: 6 December 2000 相似文献
16.
In this paper we report the identification and characterization of a DNA region containing putative mcpA-like gene coding for a Methyl Accepting Chemotaxis Protein (MCP) and belonging to a Burkholderia endosymbiont of the arbuscular mycorrhizal fungus Gigaspora margarita. A genomic library of total DNA extracted from the fungal spores, representative of the bacterial genome, was used to investigate
the prokaryotic genome. PCR experiments with primers designed on the Burkholderia mcpA-like gene and Southern blot analysis demonstrate that they actually belong to the genome of G. margarita endosymbiont. The expression of the mcpA-like gene in the fungal spores was demonstrated by RT-PCR experiments. The detailed comparative analysis of the bacterial
MCPs available in databases allowed to draw a possible evolutionary pathway leading to the present-day mcpA genes. Accordingly, the ancestor of the mcpA-like genes was the result of a domain shuffling event involving two ancestral mini-genes encoding a PAS-PAC and a MA domains,
respectively, followed by the elongation of the PAS-PAC moiety. The following evolutionary divergence involved not only point
mutations, but also larger rearrangements (insertions and deletions) at the 3′ end of the gene. 相似文献
17.
Nuria Saperas Manel Chiva David C. Pfeiffer Harold E. Kasinsky Juan Ausió 《Journal of molecular evolution》1997,44(4):422-431
We have characterized for the first time SNBPs from the hagfish Eptatratus stouti (Myxini) and the lamprey Lampetra tridentatus (Cephalaspidomorphi) and have found that histones are the major protein components of the sperm of these agnathans. We have
also conducted a systematic analysis of SNBPs from different groups of chondrichthyan fishes, including the skate Raja rhina and seven species of sharks. Together with our previous data showing the sporadic nature of SNBP evolution in bony fish (Saperas,
N., Ausio, J., Lloris, D. and Chiva, M. [1994] J. Mol. Evol. 39: 282–295), the present study provides a unique insight into the overall evolutionary complexity and variability of the
nuclear sperm proteins of fishes. It would appear that despite the discontinuous evolution of these proteins, the macroevolutionary
pattern of histone (H type) → protamine-like (PL type) → protamine (P type) has been conserved in fish evolution, as it has
in the evolution of other Deuterostomes.
Received: 11 June 1996 / Accepted: 6 August 1996 相似文献
18.
Thirty complete coding sequences of human major histocompatibility complex (Mhc) class II DRB alleles, spanning 237 codons, were analyzed for phylogenetic information using distance, parsimony, and likelihood approaches.
Allelic genealogies derived from different parts of the coding sequence (exon 2, the 5′ and 3′ ends of exon 2, respectively,
and exons 3–6) were compared. Contrary to prior assertions, a rigorous analysis of allelic genealogies in this gene family
cannot be used to justify the claim that the lineage leading to modern humans contained on average at least 100,000 individuals.
Phylogenetic inferences based upon the exon 2 region of the DRB loci are complicated by selection and recombination, so this part of the gene does not provide a complete and accurate view
of allelic relationships. Attempts to reconstruct human history from genetic data must use realistic models which consider
the complicating factors of nonequilibrium populations, recombination, and different patterns of selection.
Received: 19 February 1997 / Accepted: 12 June 1997 相似文献
19.
Nuclear magnetic resonance (NMR) microimaging and proton relaxation times were used to monitor differences between the hydration
state of the nucleus and cytoplasm in the Rana pipiens oocyte. Individual isolated ovarian oocytes were imaged in a drop of Ringer's solution with an in-plane resolution of 80
μm. Proton spin echo images of oocytes arrested in prophase I indicated a marked difference in contrast between nucleoplasm
and cytoplasm with additional intensity gradations between the yolk platelet-rich region of the cytoplasm and regions with
little yolk. Neither shortening τe (spin echo time) to 9 msec (from 18 msec) nor lengthening τr (spin recovery time) to 2 sec (from 0.5 sec) reduced the observed contrast between nucleus and cytoplasm. Water proton T1 (spin-lattice) relaxation times of oocyte suspensions indicated three water compartments that corresponded to extracellular
medium (T1= 3.0 sec), cytoplasm (T1= 0.8 sec) and nucleoplasm (T1= 1.6 sec). The 1.6 sec compartment disappeared at the time of nuclear breakdown. Measurements of plasma and nuclear membrane
potentials with KCl-filled glass microelectrodes demonstrated that the prophase I oocyte nucleus was about 25 mV inside positive
relative to the extracellular medium. A model for the prophase-arrested oocyte is proposed in which a high concentration of
large impermeant ions together with small counter ions set up a Donnan-type equilibrium that results in an increased distribution
of water within the nucleus in comparison with the cytosol. This study indicates: (i) a slow exchange between two or more
intracellular water compartments on the NMR time-scale, (ii) an increased rotational correlation time for water molecules
in both the cytoplasmic and nuclear compartments compared to bulk water, and (iii) a higher water content (per unit dry mass)
of the nucleus compared to the cytoplasm, and (iv) the existence of a large (about 75 mV positive) electropotential difference
between the nuclear and cytoplasmic compartments.
Received: 18 January 1996/Revised: 29 April 1996 相似文献
20.
The presence and localization of voltage-gated Ca2+ channels of L-type were investigated in intestinal cells of the Atlantic cod. Enterocytes were loaded with the fluorescent
Ca2+ probe, fure-2/AM and changes in intracellular Ca2+ concentrations ([Ca2+]
i
) were measured, in cell suspensions, in the presence of high potassium levels (100 mm), BAY K-8644 (5 μm), nifedipine (5 μm) or ω-conotoxin (1 μm). L-type Ca2+ channels were visualized on intestinal sections using the fluorescent dihydropyridine (-)-STBodipy.
Depolarization of the plasma membrane produced a rapid (within 5 sec) and transient (at basal levels after 21 sec) increase
in [Ca2+]
i
. BAY K-8644 increased the [Ca2+]
i
by 7.2%. Cells in a Ca2+-free buffer increased [Ca2+]
i
after addition of 10 mm Ca2+, and this increase was abolished by nifedipine in both depolarizing and normal medium but not by ω-conotoxin. Single cell
experiments using video microscopy revealed that enterocytes remained polarized several hours after preparation and that the
Ca2+ entry and extrusion occurred at specific and different regions of the enterocyte outer membrane. Fluorescent staining of
L-type Ca2+ channels in the intestinal mucosa showed the most intense staining at the brushborder membrane.
These results demonstrate the presence of voltage gated L-type Ca2+ channels in enterocytes from the Atlantic cod. The channels are mainly located at the apical side of the cells, and there
is a polarized uptake of Ca2+ into the enterocytes. This suggests that the L-type Ca2+ channels are involved in the transcellular Ca2+ entry into the enterocytes.
Received: 21 August 1997/Revised: 15 April 1998 相似文献