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1.
The peptide bond formation of alanine (ala), ala + glycine (gly), ala + diglycine (gly2), and ala + gly cyclic anhydride (cyc-gly2) in drying/wetting cycles at 80°C was studied. Silica, alumina, and representative smectites—montmorillonite and hectorite—were
used as catalysts, and the dependence of reaction yields on the available amount of water in the reaction systems was evaluated.
Silica and alumina catalyze the formation of oligopeptide mainly in temperature fluctuation experiments, whereas higher amounts
of water in the reaction system support clay-catalyzed reactions. Silica and alumina are much more efficient for amino acid
dimerization than clays. Whereas only 0.1% of ala oligomerized on hectorite and no reaction proceeded on montmorillonite,
about 0.9 and 3.8% alanine converted into its dimer and cyclic anhydride on silica and alumina, respectively. Clay minerals,
on the other hand, seem to more efficiently catalyze peptide chain elongation than amino acid dimerization. The reaction yields
of ala-gly-gly and gly-gly-ala from ala + gly2 and ala + cyc-gly2 reached about 0.3% on montmorillonite and 1.0% on hectorite. The possible mechanisms of these reactions and the relevance
of the results for prebiotic chemistry are discussed.
Received: 15 December 1996 / Accepted: 1 May 1997 相似文献
2.
Timothy L. Porter Michael P. Eastman Michael E. Hagerman Lance B. Price Richard F. Shand 《Journal of molecular evolution》1998,47(4):373-377
Condensation reactions of the amino acid glycine on the surface of Cu(II)-exchanged hectorite are investigated using the
technique of scanning force microscopy. Prebiotic conditions are simulated using alternate wetting and heating cycles. Concentration,
immobilization, and subsequent polymerization resulting in glycine oligomers are seen to occur primarily at step edges or
faults in the topmost layer. Condensation reactions also occur within tiny micropores or defects in the topmost layer. These
reactions are facilitated by the availability of intergallery metal cations at the step edges or pores in the surface region.
Received: 19 January 1998 / Accepted: 24 April 1998 相似文献
3.
In the first part of this study, photofrin II sensitized membrane modifications of OK-cells were investigated at the level
of macroscopic membrane currents. In this second part, the inside-out configuration of the patch-clamp technique is applied
to analyze the phenomena at the microscopic level. It is shown that the characteristic single channel fluctuations of the
electric current disappear after the start of illumination of membrane patches in the presence of photofrin II. This holds
for all three types of ion channels investigated: the large-conductance Ca2+-dependent K+ channel (maxi-KCa), a K+ channel of small conductance (sK), and a stretch-activated nonselective cation channel (SA-cat). Part of the experiments
show a transient activation of the channels (indicated by an increase of the probability in the open-channel state) before
the channels are converted into a closed nonconductive state. Inactivation of all three channel types proceeds by a continuous
reduction of their open probability, while the single channel conductance values are not affected. The process of photodynamically
induced channel inactivation is followed by a pronounced increase of the leak conductance of the plasma membrane. The latter
process — after light-induced initiation — is found to continue in the dark. The ionic pathways underlying the leak conductance
also allow permeation of Ca2+ ions. The resulting Ca2+-flux may contribute to the photodynamically induced increase of the intracellular Ca2+ concentration observed in various cell lines.
Received: 26 May 1998/Revised: 8 September 1998 相似文献
4.
Extensive Sequence Conservation Among Insect,Nematode, and Vertebrate Vitellogenins Reveals Ancient Common Ancestry 总被引:10,自引:0,他引:10
Jeng-Shong Chen Thomas W. Sappington Alexander S. Raikhel 《Journal of molecular evolution》1997,44(4):440-451
The eggs of most oviparous animals are provisioned with a class of protein called vitellogenin (Vg) which is stored as the
major component of yolk. Until recently, deduced amino acid sequences were available only from vertebrate and nematode Vgs,
which proved to be homologous. The sequences of several insect Vgs are now known, but early attempts at pairwise alignments
with vertebrate and nematode Vgs have been problematic, leading to conflicting conclusions about how closely insect Vgs are
related to the others. In this paper we demonstrate that insect Vg sequences can be confidently aligned with one another along
their entire lengths and with multiple vertebrate and nematode Vg sequences along most of their spans. Although divergence
is high, conservation among insect, vertebrate, and nematode Vg sequences is widespread with a preponderance of glycine, proline,
and cysteine residues among strictly conserved amino acids, establishing conclusively that Vgs from the three phyla are homologous.
Areas of least-certain alignment are primarily in and around insect and vertebrate polyserine domains which are not homologous.
Phylogenetic reconstructions of Vgs based on sequence identities indicate that the insect lineage is the most diverged and
that the mammalian serum protein, apolipoprotein B-100, arose from a Vg ancestor after the nematode/vertebrate divergence.
Received: 6 May 1996 / Accepted: 27 September 1996 相似文献
5.
P. S. Leung H. C. Chan L. X. M. Fu P. Y. Leung S. B. C. Chew P. Y. D. Wong 《The Journal of membrane biology》1997,157(1):97-103
Correspondence to: H.C. Chan-->
Abstract. Previous studies from our laboratory have provided evidence for the existence of a local renin-angiotensin system in the
rat epididymis. Evidence has also accumulated, indicating that locally formed angiotensin II from the rat epididymis may play
a paracrine and/or autocrine role in regulating epididymal electrolyte and fluid transport. In the present study, specific
anti-peptide antibodies against the second extracellular loops of angiotensin II type I (AT1) and type II (AT2) receptors were used to localize immunocytochemically these receptors in the rat cauda epididymides of three developmental
stages, namely, immature (2-week), early mature (6-week) and fully mature (10-week). The immunostaining intensity for AT1 receptors was found to be stronger than that for AT2 receptors throughout rat epididymides of all stages. However, the immunostaining for both AT1 and AT2 receptors observed in the fully mature rat epididymis was much more intense than that observed in the epididymides of the
two younger stages. While the immunostaining for both AT1 and AT2 receptors in the younger rat epididymides appeared to be distributed in both basal and apical regions, the immunostaining
in the fully mature epididymis was predominantly localized in the basal region. The present finding of the differential patterns
of angiotensin II receptor immunoreactivity in three different stages of the rat epididymis may reflect the fine tuning of
rat epididymal function by angiotensin II, acting as a paracrine or autocrine agent, during the course of development.
Received: 18 December 1995/Revised: 19 December 1996 相似文献
6.
Gene structure of a chlorophyll a/c-binding protein from a brown alga: Presence of an intron and phylogenetic implications 总被引:5,自引:0,他引:5
Lise Caron Dominique Douady Michelle Quinet-Szely Susan de Goër Claire Berkaloff 《Journal of molecular evolution》1996,43(3):270-280
A Laminaria saccharina genomic library in the phage EMBL 4 was used to isolate and sequence a full-length gene encoding a fucoxanthin-chlorophyll
a/c-binding protein. Contrary to diatom homologues, the coding sequence is interrupted by an intron of about 900 bp which
is located in the middle of the transit peptide. The deduced amino acid sequence of the mature protein is very similar to
those of related proteins from Macrocystis pyrifera (Laminariales) and, to a lesser extent, to those from diatoms and Chrysophyceae. Seven of the eight putative chlorophyll-binding
amino acids determined in green plants are also present. Alignments of different sequences related to the light-harvesting
proteins (LHC) demonstrate a structural similarity among the three transmembrane helices and suggest a unique ancestral helix
preceded by two β-turns. The β-turns are conserved in front of the second helices of the chlorophyll a/c proteins more so
than in chlorophyll a/b proteins. Phylogenetic trees generated from sequence data indicate that fucoxanthin-chlorophyll-binding
proteins diverged prior to the separation of photosystem I and photosystem II LHC genes of green plants. Among the fucoxanthin-containing
algae, LHC I or II families could not be distinguished at this time.
Received: 14 February 1996 / Accepted: 4 April 1996 相似文献
7.
The present study shows that in trout red blood cells the activity of some amino acid carriers, not directly involved in
cell volume regulation, is affected by external osmolality. Glycine uptake has been used as the experimental approach because
it was shown previously that it is effected by different carriers, namely the Na+-dependent ASC and Gly systems, as well as the Na+-independent asc and L systems.
An increase in the uptake through the Gly system and the two Na+-independent carriers was found, while the ASC system appeared to be downregulated. Those systems whose activities were increased
by hypo-osmolality did not share the mechanism by which this increase was obtained. Thus, the Gly system was sensitive to
intracellular ionic changes, while the Na+- independent systems were mechanically stimulated, as assessed by the iso-osmotic swelling caused by ammonium chloride.
On the other hand, a volume-sensitive transporter may be present in trout red blood cells, which is involved in the swelling-induced
glycine movement, as can be deduced from the effect of some inhibitors such as pyridoxal phosphate, DIDS (4,4′-diisothiocyanate-stilbene-2,2′-disulfonic
acid) and quinine.
Received: 12 February 1996/Revised: 9 September 1996 相似文献
8.
J.D.H. Bursell J. Kirk S.T. Hall A.M. Gero K. Kirk 《The Journal of membrane biology》1996,154(2):131-141
The unicellular protozoan parasite, Crithidia luciliae, responded to osmotic swelling by undergoing a regulatory volume decrease. This process was accompanied by the efflux of amino
acids (predominantly alanine, proline and glycine). The relative loss of the electroneutral amino acids proline, valine, alanine
and glycine was greater than that for the anionic amino acid, glutamate; there was negligible loss of the cationic amino acids,
lysine, arginine and ornithine. The characteristics of amino acid release were investigated using a radiolabeled form of the
nonmetabolized alanine analogue α-aminoisobutyrate. α-Aminoisobutyrate efflux was activated within a few seconds of a reduction
of the osmolality, and inactivated rapidly (again within a few seconds) on restoration of isotonicity. The initial rate of
efflux of α-aminoisobutyrate from cells in hypotonic medium was unaffected by the extracellular amino acid concentration.
Hypotonically activated α-aminoisobutyrate efflux (as well as the associated regulatory volume decrease) was inhibited by
the sulfhydryl reagent N-ethylmaleimide but was not inhibited by a range of anion transport blockers. As in the efflux experiments, unidirectional
influx rates for α-aminoisobutyrate increased markedly following reduction of the osmolality, consistent with the swelling-activated
amino acid release mechanism allowing the flux of solutes in both directions. Hypotonically activated α-aminoisobutyrate influx
showed no tendency to saturate up to an extracellular concentration of 50 mm. The functional characteristics of the amino acid release mechanism are those of a channel, with a preference for electroneutral
and anionic amino acids over cationic amino acids. However, the pharmacology of the system differs from that of the anion-selective
channels that are thought to mediate the volume-regulatory efflux of organic osmolytes from vertebrate cells.
Received: 13 May 1996/Revised: 9 July 1996 相似文献
9.
Evolutionary Relationship of the Ligand-Gated Ion Channels and the Avermectin-Sensitive,Glutamate-Gated Chloride Channels 总被引:4,自引:0,他引:4
Demetrios K. Vassilatis Keith O. Elliston Philip S. Paress Michel Hamelin Joseph P. Arena James M. Schaeffer Lex H.T. Van der Ploeg Doris F. Cully 《Journal of molecular evolution》1997,44(5):501-508
Two cDNAs, GluClα and GluClβ, encoding glutamate-gated chloride channel subunits that represent targets of the avermectin
class of antiparasitic compounds, have recently been cloned from Caenorhabditis elegans (Cully et al., Nature, 371, 707–711, 1994). Expression studies in Xenopus oocytes showed that GluClα and GluClβ have pharmacological profiles distinct from the glutamate-gated cation channels as
well as the γ-aminobutyric acid (GABA)- and glycine-gated chloride channels. Establishing the evolutionary relationship of
related proteins can clarify properties and lead to predictions about their structure and function. We have cloned and determined
the nucleotide sequence of the GluClα and GluClβ genes. In an attempt to understand the evolutionary relationship of these
channels with the members of the ligand-gated ion channel superfamily, we have performed gene structure comparisons and phylogenetic
analyses of their nucleotide and predicted amino acid sequences. Gene structure comparisons reveal the presence of several
intron positions that are not found in the ligand-gated ion channel superfamily, outlining their distinct evolutionary position.
Phylogenetic analyses indicate that GluClα and GluClβ form a monophyletic subbranch in the ligand-gated ion channel superfamily
and are related to vertebrate glycine channels/receptors. Glutamate-gated chloride channels, with electrophysiological properties
similar to GluClα and GluClβ, have been described in insects and crustaceans, suggesting that the glutamate-gated chloride
channel family may be conserved in other invertebrate species. The gene structure and phylogenetic analyses in combination
with the distinct pharmacological properties demonstrate that GluClα and GluClβ belong to a discrete ligand-gated ion channel
family that may represent genes orthologous to the vertebrate glycine channels.
Received: 30 September 1996 / Accepted: 15 November 1996 相似文献
10.
C.J. Giffard S. Ladha A.R. Mackie D.C. Clark D. Sanders 《The Journal of membrane biology》1996,151(3):293-300
Nisin, a prominent member of the lantibiotic family of antimicrobial agents, has wide application as a food preservative despite
poor understanding of its mode of action. Fluorescence recovery after photobleaching has been used with planar lipid bilayers
as a model membrane system to examine how nisin might interact with the surface of bacterial cells. Nisin associates with
planar lipid bilayers in the absence of an applied membrane potential causing an array of effects consistent with adsorption
of nisin onto the membrane surface which involves inhibition of the lateral diffusion and fluorescence of the lipid probe
N-(7--1,2,3-benzoxadiazol-4-yl) phosphatidylethanolamine (NBD-PE) and a reduction of the capacitance of the bilayer. Nisin
adsorption is dependent on phospholipid composition. In the presence of dioleoylphosphatidylcholine (PC): cardiolipin (CL)
4:1, the rate of lateral mobility of phospholipid is reduced to 61% of the control level which decreases to a value of 46%
when CL is replaced by 1-palmitoyl-2-oleoylphosphatidylserine (PS). These effects on bilayer parameters are transient, and
with time the values return to near original levels. High electrical conductivity is observed on application of a voltage
ramp suggesting that insertion into the membrane follows surface association. Results have been interpreted in terms of a
model in which nisin initially binds to the surface of the membrane causing a modulation of bilayer properties.
Received: 14 August 1995/Revised: 22 February 1996 相似文献
11.
When human T cell receptor for antigen (TCR) alpha chain V-genes were compared pair-wise, the numbers of nucleotide differences
showed a characteristic distribution; most were in the range of 100 to 200 differences out of a total of about 300 bases.
The same distribution was observed for mouse TCR alpha chains. Even more interesting was that comparing human alpha chains
and mouse alpha chains gave essentially the same nucleotide difference pattern. It is inferred from the large number of differences
and from the nonspecificity of trans-species (human and mouse) nucleotide sequence differences of TCR V-genes that TCR alpha
chains probably diverged early during evolution. The same feature was also observed for human and mouse TCR beta chains, although
the alpha and beta chain V-genes were distinct. This evolutionary preservation could be of vital importance to the fidelity
of the complicated trimolecular interactions among TCR alpha and beta chains, the processed peptide, and the major histocompatibility
complex (MHC) class I or II molecules.
Received: 22 January 1996 / Accepted: 9 September 1996 相似文献
12.
Wei Wu Morris Goodman Margaret I. Lomax Lawrence I. Grossman 《Journal of molecular evolution》1997,44(5):477-491
Cytochrome c oxidase (COX) is a multi-subunit enzyme complex that catalyzes the final step of electron transfer through the respiratory
chain on the mitochondrial inner membrane. Up to 13 subunits encoded by both the mitochondrial (subunits I, II, and III) and
nuclear genomes occur in eukaryotic organisms ranging from yeast to human. Previously, we observed a high number of amino
acid replacements in the human COX IV subunit compared to mouse, rat, and cow orthologues. Here we examined COX IV evolution
in the two groups of anthropoid primates, the catarrhines (hominoids, cercopithecoids) and platyrrhines (ceboids), as well
as one prosimian primate (lorisiform), by sequencing PCR-amplified portions of functional COX4 genes from genomic DNAs. Phylogenetic analysis of the COX4 sequence data revealed that accelerated nonsynonymous substitution rates were evident in the early evolution of both catarrhines
and, to a lesser extent, platyrrhines. These accelerated rates were followed later by decelerated rates, suggesting that positive
selection for adaptive amino acid replacement became purifying selection, preserving replacements that had occurred. The evidence
for positive selection was especially pronounced along the catarrhine lineage to hominoids in which the nonsynonymous rate
was first faster than the synonymous rate, then later much slower. The rates of three types of ``neutral DNA' nucleotide
substitutions (synonymous substitutions, pseudogene nucleotide substitutions, and intron nucleotide substitutions) are similar
and are consistent with previous observations of a slower rate of such substitutions in the nuclear genomes of hominoids than
in the nuclear genomes of other primate and mammalian lineages.
Received: 22 May 1996 / Accepted: 24 November 1996 相似文献
13.
Satoru Kanai Reiko Kikuno Hiroyuki Toh Haruko Ryo Takeshi Todo 《Journal of molecular evolution》1997,45(5):535-548
The photolyase–blue-light photoreceptor family is composed of cyclobutane pyrimidine dimer (CPD) photolyases, (6-4) photolyases,
and blue-light photoreceptors. CPD photolyase and (6-4) photolyase are involved in photoreactivation for CPD and (6-4) photoproducts,
respectively. CPD photolyase is classified into two subclasses, class I and II, based on amino acid sequence similarity. Blue-light
photoreceptors are essential light detectors for the early development of plants. The amino acid sequence of the receptor
is similar to those of the photolyases, although the receptor does not show the activity of photoreactivation. To investigate
the functional divergence of the family, the amino acid sequences of the proteins were aligned. The alignment suggested that
the recognition mechanisms of the cofactors and the substrate of class I CPD photolyases (class I photolyases) are different
from those of class II CPD photolyases (class II photolyases). We reconstructed the phylogenetic trees based on the alignment
by the NJ method and the ML method. The phylogenetic analysis suggested that the ancestral gene of the family had encoded
CPD photolyase and that the gene duplication of the ancestral proteins had occurred at least eight times before the divergence
between eubacteria and eukaryotes.
Received: 23 October 1996 / Accepted: 1 April 1997 相似文献
14.
J. Robert Macey Allan Larson Natalia B. Ananjeva Theodore J. Papenfuss 《Journal of molecular evolution》1997,44(6):660-674
A phylogenetic tree for major lineages of iguanian lizards is estimated from 1,488 aligned base positions (858 informative)
of newly reported mitochondrial DNA sequences representing coding regions for eight tRNAs, ND2, and portions of ND1 and COI.
Two well-supported groups are defined, the Acrodonta and the Iguanidae (sensu lato). This phylogenetic hypothesis is used
to investigate evolutionary shifts in mitochondrial gene order, origin for light-strand replication, and secondary structure
of tRNACys. These three characters shift together on the branch leading to acrodont lizards. Plate tectonics and the fossil record indicate
that these characters changed in the Jurassic. We propose that changes to the secondary structure of tRNACys may destroy function of the origin for light-strand replication which, in turn, may facilitate shifts in gene order.
Received: 28 May 1996 / Accepted: 27 December 1996 相似文献
15.
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
16.
D.B. Light M.R. Adler J.K. Ter Beest S.A. Botsford R.T. Gronau 《The Journal of membrane biology》1998,166(2):119-132
This study examined whether protein kinase C (PKC) stimulates K+ efflux during regulatory volume decrease (RVD) in Necturus maculosus (mudpuppy) red blood cells (RBCs). The limit of osmotic fragility increased with the general protein kinase inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine
(H-7, 10 μm), but not with the cyclic nucleotide-dependent kinase antagonists N-(2′-guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004,
10 μm) and N-2-(methylamino)ethyl-5-isoquinoline-sulfonamide (H-8, 5 μm). Consistent with these results, osmotic fragility also increased with the PKC antagonists bisindolylmaleimide I (GF-109203X
or bis I, 100 nm), bisindolylmaleimide II (bis II, 100 nm), and chelerythrine (10 μm). The effect of these three antagonists and H-7 was reversed with gramicidin (5 μm in a choline Ringer), indicating PKC was linked to K+ efflux (gramicidin is a cationophore that was used to ensure a high K+ permeability). We also measured cell volume recovery from hypotonic shock (0.5× Ringer) with a Coulter counter and estimated
cell volume from the hematocrit. The percent RVD compared to control decreased with H-7 (10 μm), sphingosine (100 nm), chelerythrine (10 μm), bis I (100 nm), and bis II (100 nm), but not with HA-1004 (10 μm) nor H-8 (5 μm). Inhibition of RVD by H-7, chelerythrine, bis I, and bis II was reversed with gramicidin (5 μm). Furthermore, using the patch clamp technique, we found H-7 (10 μm) reduced a whole cell conductance that was activated during cell swelling. In addition, a conductance responsible for K+ efflux during cell swelling was inhibited by bis I (100 nm) and bis II (100 nm). These results indicate that a conductive pathway mediating K+ loss during RVD is regulated, at least in part, by protein kinase C.
Received: 20 January 1998/Revised: 2 September 1998 相似文献
17.
Contribution of Mutation and RNA Recombination to the Evolution of a Plant Pathogenic RNA 总被引:10,自引:0,他引:10
Miguel A. Aranda Aurora Fraile Joaquín Dopazo José M. Malpica Fernando García-Arenal 《Journal of molecular evolution》1997,44(1):81-88
The nucleotide sequence of 17 variants of the satellite RNA of cucumber mosaic virus (CMV-satRNA) isolated from field-infected
tomato plants in the springs of 1989, 1990, and 1991 was determined. The sequence of each of the 17 satRNAs was unique and
was between 334 and 340 nucleotides in length; 57 positions were polymorphic. There was much genetic divergence, ranging from
0.006 to 0.141 nucleotide substitutions per site for pairwise comparisons, and averaging 0.074 for any pair. When the polymorphic
positions were analyzed relative to a secondary structure model proposed for CMV-satRNAs, it was found that there were significantly
different numbers of changes in base-paired and non–base-paired positions, and that mutations that did not disrupt base pairing
were preferred at the putatively paired sites. This supports the concept that the need to maintain a functional structure
may limit genetic divergence of CMV-satRNA. Phylogenetic analyses showed that the 17 CMV-satRNA variants clustered into two
subgroups, I and II, and evolutionary lines proceeding by the sequential accumulation of mutations were apparent. Three satRNA
variants were outliers for these two phylogenetic groups. They were shown to be recombinants of subgroup I and II satRNAs
by calculating phylogenies for different molecular regions and by using Sawyer's test for gene conversion. At least two recombination
events were required to produce these three recombinant satRNAs. Thus, recombinants were found to be frequent (∼17%) in natural
populations of CMV-satRNA, and recombination may make an important contribution to the generation of new variants. To our
knowledge this is the first report of data allowing the frequency of recombinant isolates in natural populations of an RNA
replicon to be estimated.
Received: 14 May 1996 / Accepted: 17 July 1996 相似文献
18.
Two Chinese hamster ovary cell (CHO-K1) mutants selected for defective glutamate transport via system X−
AG are also highly permeable to small neutral molecules. Light microscopy demonstrated that exposure of one of these mutants,
Ed-A1, to hypo-osmotic medium led to extremely rapid swelling, presumably due to increased water flux. When placed in 20%
saline, Ed-A1 cells swelled to three times their original volume within 15 sec, a sixfold larger increase than parental CHO-K1.
In spite of this rapid volume increase, mutant and wild-type cells remained viable for 20 min in dilute saline. A regulatory
volume decrease in Ed-A1, and the continual swelling of CHO-K1, resulted in the two cells achieving equal size after 5 min
in 20% saline.
The time course of these volume changes permitted analysis of large numbers of cells by a hydrodynamic technique, steric field
flow fractionation (FFF). Steric FFF demonstrated the expected inhibition of osmotic swelling of human erythrocytes by the
mercurial, p-chloromercuribenzenesulfonic acid (PCMBS). However, PCMBS increased the apparent swelling rate of Ed-A1 and CHO-K1, suggesting
that an aquaporin-like molecule is not responsible for any significant fraction of the water fluxes into either line. PCMBS
also strongly inhibited aspartate transport by system X−
AG. By taking advantage of their different swelling rates in hypotonic medium, steric FFF can separate mixtures of CHO-K1 and
Ed-A1.
Received: 2 August 1996/Revised: 25 October 1996 相似文献
19.
F. Gómez-Lagunas T. Olamendi-Portugal F.Z. Zamudio L.D. Possani 《The Journal of membrane biology》1996,152(1):49-56
Two novel peptides were purified from the venom of the scorpion Pandinus imperator, and were named Pi2 and Pi3. Their complete primary structures were determined and their blocking effects on Shaker B K+ channels were studied. Both peptides contain 35 amino acids residues, compacted by three disulfide bridges, and reversibly
block the Shaker B K+ channels. They have only one amino acid changed in their sequence, at position 7 (a proline for a glutamic acid). Whereas
peptide Pi2, containing the Pro7, binds the Shaker B K+ channels with a K
d
of 8.2 nm, peptide Pi3 containing the Glu7 residue has a much lower affinity of 140 nm. Both peptides are capable of displacing the binding of 125I-noxiustoxin to brain synaptosome membranes. Since these two novel peptides are about 50% identical to noxiustoxin, the present
results support previous data published by our group showing that the amino-terminal region of noxiustoxin, and also the amino-terminal
sequence of the newly purified homologues: Pi2, and Pi3, are important for the recognition of potassium channels.
Received: 13 November 1995/Revised: 11 March 1996 相似文献
20.
E. Modesto P. D. Lampe M. C. Ribeiro D. C. Spray A. C. Campos de Carvalho 《The Journal of membrane biology》1996,154(3):239-249
Membrane fractions highly enriched in chicken lens MIP (MIP28) were found to form ion channels when incorporated into planar
lipid bilayers. The channels displayed prominent unitary conductances of about 60 and 290 pS in symmetric 150 mm KCl solution and were slightly anion selective. For both depolarizing and hyperpolarizing voltages, voltage sensitivity of
the MIP28-induced conductance could be fit by a Boltzmann relation, symmetric around zero mV, with V
0
= 18.5 mV, n= 4.5 and g
min/g
max= 0.17. Channel properties were not appreciably altered by pH in the range of 5.8 to 7, although channel incorporation was
observed to occur more frequently at lower pH values. Calcium, at millimolar concentrations, decreased the channel mean open
time. Partial proteolysis of MIP28 to yield MIP21 did not appreciably affect single-channel conductance or voltage sensitivity
of the reconstituted channels. MIP28 was not phosphorylated by cAMP dependent protein kinase (PKA). Although unitary conductance
and selectivity of the chicken MIP channel are similar to those reported for the bovine MIP (MIP26), the voltage sensitivity
of MIP28 was higher than that of the bovine homologue, and voltage sensitivity of MIP28 was not modulated by treatments previously
shown to affect MIP26 voltage gating (partial proteolysis and protein phosphorylation by PKA: (Ehring et al., 1990). The existence
of such strikingly different functional properties in highly homologous channel isoforms may provide a useful system for exploration
of the structure-function relations of MIP channels.
Received: 27 March 1996/Revised: 5 August 1996 相似文献