共查询到20条相似文献,搜索用时 31 毫秒
1.
Patricia E. López-Calcagno Johanna Moreno Luis Cedeño Luis Labrador Juan L. Concepción Luisana Avilán 《Mycological Research》2009,113(6-7):771-781
The genes of the mitochondrial and cytosolic malate dehydrogenase (mMDH and cMDH) of Phytophthora infestans were cloned and overexpressed in Escherichia coli as active enzymes. The catalytic properties of these proteins were determined: both enzymes have a similar specific activity. In addition, the natural mitochondrial isoenzyme was semi-purified from mycelia and its catalytic properties determined: the recombinant mitochondrial isoform behaved as the natural enzyme. A phylogenetic analysis indicated that mMDH, present in all stramenopiles studied, can be useful to study the relationships between these organisms. MDH with the conserved domain MDH_cytoplasmic_cytosolic is absent in some stramenopiles as well as in fungi. This enzyme seems to be less related within the stramenopile group. The Phytophthora cMDHs have an insertion of six amino acids that is also present in the stramenopile cMDHs studied, with the exception of Thalassiosira pseudonana cMDH, and is absent in other known eukaryotic cMDHs. 相似文献
2.
Because the mitochondrial inner membrane is impermeable to pyridine nucleotides, transport of reducing equivalents between the mitochondrial matrix and the cytoplasm relies on shuttle mechanisms, including the malate-aspartate shuttle and the glycerol-3-phosphate shuttle. These shuttles are needed for reducing equivalents generated by metabolic reactions in the cytosol to be oxidized via aerobic metabolism. Two isoenzymes of malate dehydrogenase (MDH) operate as components of the malate-aspartate shuttle, in which a reducing equivalent is transported via malate, which when oxidized to oxaloacetate, transfers an electron pair to reduce NAD to NADH. Several competing mechanisms have been proposed for the MDH-catalyzed reaction. This study aims to identify the pH-dependent kinetic mechanism for cytoplasmic MDH (cMDH) catalyzed oxidation/reduction of MAL/OAA. Experiments were conducted assaying the forward and reverse directions with products initially present, varying pH between 6.5 and 9.0. By fitting time-course data to various mechanisms, it is determined that an ordered bi-bi mechanism with coenzyme binding first followed by the binding of substrate is able to explain the kinetic data. The proposed mechanism is similar to, but not identical to, the mechanism recently determined for the mitochondrial isoform, mMDH. cMDH and mMDH mechanisms are also shown to both be reduced versions of a common, more complex mechanism that can explain the kinetic data for both isoforms. Comparing the simulated activity (ratio of initial velocity to the enzyme concentration) under physiological conditions, the mitochondrial MDH (mMDH) activity is predicted to be higher than cMDH activity under mitochondrial matrix conditions while the cMDH activity is higher than mMDH activity under cytoplasmic conditions, suggesting that the functions of the isoforms are kinetically tuned to their individual physiological roles. 相似文献
3.
The evolutionary history of the malate dehydrogenase (MDH) gene family [NAD-dependent MDH; EC 1.1.1.37 and NAD(P)-dependent MDH; EC 1.1.1.82] has received much attention. MDHs have also featured extensively as electrophoretic markers in population genetics and evolutionary ecology, and in many cases, intraspecific variation in MDH has been correlated with environmental variables. However, while the amino acid residues essential for MDH function are known, no studies have examined intraspecific nucleotide variation despite evidence indicating that natural selection may be operating on this locus. This study presents two sets of degenerate oligonucleotide PCR primers to facilitate the cloning of cytosolic MDH (cMDH) and mitochondrial MDH (mMDH) from a broad range of animals (cMDH) and animals and plants (mMDH). These primers were used to obtain putative cMDH and mMDH cDNAs from the mollusc Nucella lapillus. The N. lapillus cMDH cDNA was found to encode a putative cMDH protein of 334aa and 36kDa, while the mMDH cDNA encoded a putative mature mMDH protein of 315aa and 33kDa. The putative amino acid sequences of the two compartmentalised N. lapillus MDHs are presented and compared to other known MDH sequences. 相似文献
4.
Clonorchis sinensis: molecular cloning and functional expression of novel cytosolic malate dehydrogenase 总被引:14,自引:0,他引:14
Zheng N Xu J Wu Z Chen J Hu X Song L Yang G Ji C Chen S Gu S Ying K Yu X 《Experimental parasitology》2005,109(4):220-227
The NAD-dependent cytosolic malate dehydrogenase (cMDH, EC 1.1.1.37) plays a pivotal role in the malate-aspartate shuttle pathway that operates in a metabolic coordination between cytosol and mitochondria, and thus is crucial for the survival and pathogenicity of the parasite. In the high throughput sequencing of the cDNA library constructed from the adult stage of Clonorchis sinensis, a cDNA clone containing 1152bp insert was identified to encode a putative peptide of 329 amino acids possessing more than 50% amino acid sequence identities with the cMDHs from other organisms such as fish, plant, and mammal. But low sequence similarities have been found between this cMDH and mitochondrial malate dehydrogenase as well as glyoxysomal malate dehydrogenase from other organisms. Northern blot analysis showed the size of the C. sinensis cMDH mRNA was 1.2 kb. The cMDH was expressed in Escherichia coli M15 as a His-tag fusion protein and purified by BD TALON metal affinity column. The recombinant cMDH showed high MDH activity of 241 U mg(-1), without lactate dehydrogenase and NADP(H) selectivity. It provides a model for the structure, function analysis, and drug screening on cMDH. 相似文献
5.
T Joh H Takeshima T Tsuzuki C Setoyama K Shimada S Tanase S Kuramitsu H Kagamiyama Y Morino 《The Journal of biological chemistry》1987,262(31):15127-15131
A cDNA clone, named ppcMDH-1 and covering a part of the coding region for the porcine cytosolic malate dehydrogenase (cMDH) mRNA, was isolated from a porcine liver cDNA library. Subsequently, mouse cMDH cDNA clones were isolated from mouse liver and heart cDNA libraries, using the ppcMDH-1 cDNA as a probe. The longest clone, named pmcMDH-5, was sequenced and the primary structure of the mouse cMDH deduced from its cDNA sequence showed that the mouse cMDH consists of the 334-amino acid residues. When the amino acid sequence of the mouse cMDH was compared with that of the porcine cMDH, they shared a 93% homology. On the other hand, the amino acid sequences of mouse cMDH and mitochondrial MDH (mMDH) showed about 23% overall homology. Surprisingly, comparison of the amino acid sequences among the mammalian and bacterial MDHs revealed that the homology between the mouse cMDH and thermophilic bacterial MDH, as well as the homology between the mouse mMDH and Escherichia coli MDH, markedly exceeds the intraspecies sequence homology between mMDH and cMDH from mice. 相似文献
6.
S. Strumilo A. Owsieniuk A. Radecka A. Tylicki 《Journal of Evolutionary Biochemistry and Physiology》2006,42(5):566-569
The hare heart mitochondrial malate dehydrogenase (mMDH) was established to have a much higher electrophoretic mobility than the corresponding enzyme from the rabbit heart. Differences of kinetic properties of both mMDH and cytoplasmic malate dehydrogenase (cMDH) from these two sources were shown. The hare heart mMDH and cMDH isoenzymes have a higher affinity to malate (in direct reaction) and oxaloacetate and NADH (in reverse reaction), i.e., they have lower K M values in comparison with the isoenzymes from the rabbit heart. Malate dehydrogenase seems to operate more effectively in the hare heart, which might be important in adaptive and evolutionary aspects. 相似文献
7.
Since the malate-aspartate shuttle in brain has been shown to be closely linked to brain energy metabolism and neurotransmitter synthesis, the activity of MDH, one of the enzymes of the malateaspartate shuttle, was studied in cortical non-synaptic mitochondria (mMDH) and cytosol (cMDH) in 1–4 day, 18–20 day and 7–8 week old rats. The mean mMDH activity (nmol/min/mg protein) was 10,517±734 (mean±SEM), 8,882±241 and 10,323±561 and cMDH activity was 2,453±99, 4,673±152 and 6,821±205 in 1–4 day, 18–20 day and 7–8 week old rats, respectively. While cMDH activity increased with age (p<0.0001), mMDH activity showed no change. This study also determined if endogenous compounds, previously shown to alter malate metabolism, affected MDH activities. Lactate inhibited only cMDH activity, by a competitive mechanism. Oxaloacetate inhibited mMDH by partial non-competitive inhibition and cMDH by competitive inhibition. Alpha-ketoglutarate competitively inhibited both enzymes; however, the inhibition of mMDH activity was more pronounced than that of cMDH activity. Citrate inhibited mMDH via an uncompetitive mechanism and cMDH via a noncompetitive mechanism. The mechanisms of inhibition of mMDH and cMDH by each of the effectors were the same over the three ages. The results suggest mMDH and cMDH activities show a dissimilar developmental pattern and may be regulated differently by endogenous effectors. The greater sensitivity of mMDH, compared to cMDH, to certain effectors may be related to the dual role of mMDH in the tricarboxylic acid cycle and the malate-aspartate shuttle.These data were presented in part at the meeting of the Federation of American Societies for Experimental Biology in Atlanta, Georgia, April 1991. This work was performed in partial fulfillment of the requirements for the M.S. Degree in Nutritional Sciences (P.M.) 相似文献
8.
Gel exclusion chromatographic studies demonstrate that cytosolic and mitochondrial malate dehydrogenases (cMDH and mMDH) dissociate into subunits in the presence of 0.1% of the non-ionic detergent Triton X-100 (TX-100). The presence of cofactor and catalytically competent cofactor-substrate pairs does not protect mMDH against this dissociation. In contrast, cMDH dimers resist dissociation in the presence of either addition. Since steady state kinetic studies indicate both enzymes are fully active in the presence of 0.1% TX-100, we conclude that quaternary structure is not a kinetically important feature of mMDH structure and cooperativity does not account for mMDH kinetic anomalies. In contrast, cooperativity is a reasonable explanation for cMDH kinetic properties even in the presence of 0.1% TX-100, since this enzyme's subunits associate in the presence of active site ligands. The existence of fully active mMDH subunits raises the possibility that this species rather than the dimer may be a constituent of proposed multi-enzyme complexes of the mitochondrion. Preliminary chromatographic experiments involving gently disrupted mitochondria have found MDH activity in differently sized complexes, all with molecular weights larger than the mMDH dimer but smaller than complexes anticipated for multi-enzyme complexes involving other enzymes and the mMDH dimer. 相似文献
9.
The plasma membrane calcium pump, which ejects Ca2+ from the cell, is regulated by calmodulin. In the absence of calmodulin, the pump is relatively inactive; binding of calmodulin
to a specific domain stimulates its activity. Phosphorylation of the pump with protein kinase C or A may modify this regulation.
Most of the regulatory functions of the enzyme are concentrated in a region at the carboxyl terminus. This region varies substantially
between different isoforms of the pump, causing substantial differences in regulatory properties. The pump shares some motifs
of the carboxyl terminus with otherwise unrelated proteins: The calmodulin-binding domain is a modified IQ motif (a motif
which is present in myosins) and the last 3 residues of isoform 4b are a PDZ target domain. The pump is ubiquitous, with isoforms
1 and 4 of the pump being more widely distributed than 2 and 3. In some kinds of cells isoform 1 or 4 is missing, and is replaced
by another isoform.
Received: 26 January 1998/Revised: 6 April 1998 相似文献
10.
Evolution of the 14-3-3 Protein Family: Does the Large Number of Isoforms in Multicellular Organisms Reflect Functional Specificity? 总被引:1,自引:0,他引:1
Rosenquist M Sehnke P Ferl RJ Sommarin M Larsson C 《Journal of molecular evolution》2000,51(5):446-458
14-3-3 proteins constitute a family of eukaryotic proteins that are key regulators of a large number of processes ranging
from mitosis to apoptosis. 14-3-3s function as dimers and bind to particular motifs in their target proteins. To date, 14-3-3s
have been implicated in regulation or stabilization of more than 35 different proteins. This number is probably only a fraction
of the number of proteins that 14-3-3s bind to, as reports of new target proteins have become more frequent. An examination
of 14-3-3 entries in the public databases reveals 153 isoforms, including alleloforms, reported in 48 different species. The
number of isoforms range from 2, in the unicellular organism Saccharomyces cerevisiae, to 12 in the multicellular organism Arabidopsis thaliana. A phylogenetic analysis reveals that there are four major evolutionary lineages: Viridiplantae (plants), Fungi, Alveolata,
and Metazoa (animals). A close examination of the aligned amino acid sequences identifies conserved amino acid residues and
regions of importance for monomer stabilization, dimer formation, target protein binding, and the nuclear export function.
Given the fact that 53% of the protein is conserved, including all amino acid residues in the target binding groove of the
14-3-3 monomer, one might expect little to no isoform specificity for target protein binding. However, using surface plasmon
resonance we show that there are large differences in affinity between nine 14-3-3 isoforms of A. thaliana and a target peptide representing a novel binding motif present in the C terminus of the plant plasma membrane H+ATPase. Thus, our data suggest that one reason for the large number of isoforms found in multicellular organisms is isoform-specific
functions.
Received: 19 April 2000 / Accepted: 24 July 2000 相似文献
11.
Vernal J Fiser A Sali A Müller M Cazzulo JJ Nowicki C 《Biochemical and biophysical research communications》2002,293(1):633-639
The aromatic l-alpha-hydroxy acid dehydrogenase (AHDAH) from Trypanosoma cruzi has over 50% sequence identity with cytosolic malate dehydrogenases (cMDHs), yet it is unable to reduce oxaloacetate. Molecular modeling of the three-dimensional structure of AHADH using the pig cMDH as template directed the construction of several mutants. AHADH shares with MDHs the essential catalytic residues H195 and R171 (using Eventoff's numbering). The AHADH A102R mutant became able to reduce oxaloacetate, while remaining fully active towards aromatic alpha-oxoacids. The Y237G mutant diminished its affinity for all of the natural substrates, whereas the double mutant A102R/Y237G was more active than Y237G and had similar activity with oxaloacetate and with aromatic substrates. The present results reinforce our proposal that AHADH arose by a moderate number of point mutations from a cMDH no longer present in the parasite. 相似文献
12.
Positive Darwinian Selection Promotes Heterogeneity Among Members of the Antifreeze Protein Multigene Family 总被引:9,自引:0,他引:9
A variety of organisms have independently evolved proteins exhibiting antifreeze activity that allows survival at subfreezing
temperatures. The antifreeze proteins (AFPs) bind ice nuclei and depress the freezing point by a noncolligative absorption–inhibition
mechanism. Many organisms have a heterogeneous suite of AFPs with variation in primary sequence between paralogous loci. Here,
we demonstrate that the diversification of the AFP paralogues is promoted by positive Darwinian selection in two independently
evolved AFPs from fish and beetle. First, we demonstrate an elevated rate of nonsynonymous substitutions compared to synonymous
substitutions in the mature protein coding region. Second, we perform phylogeny-based tests of selection to demonstrate a
subset of codons is subjected to positive selection. When mapped onto the three-dimensional structure of the fish antifreeze
type III antifreeze structure, these codons correspond to amino acid positions that surround but do not interrupt the putative
ice-binding surface. The selective agent may be related to efficient binding to diverse ice surfaces or some other aspect
of AFP function.
Received: 27 February 2001 / Accepted: 12 September 2001 相似文献
13.
In previous studies, we showed that lacrimal gland acini express three isoforms of protein kinase C (PKC): PKCα,-δ, and -ε.
In the present study, we report the identification of two other PKC isoforms, namely PKCμ and -ι/λ. Using immunofluorescence
techniques, we showed that these isoforms are differentially located. PKCα and -μ showed the most prominent membrane localization,
whereas PKCδ, -ε and -ι/λ were mainly cytosolic. Using cell fractionation and western blotting techniques, we showed that
the phorbol ester, phorbol 12, 13-dibutyrate (PdBu, 10−6
m), translocated all PKC isoforms, except PKCι/λ, from the soluble fraction into the particulate fraction. The effect was maximum
at 5 min and persisted at 10 min. PKCε was the most responsive to PdBu reaching almost maximal translocation at a PdBu concentration
as low as 10−9
m. The cholinergic agonist, carbachol (10−5 and 10−3
m), induced translocation which was transient for PKCδ, and -μ, but persisted for 10 min for PKCε. Carbachol did not translocate
PKCα and, like PdBu, did not translocate PKCι/λ. We concluded that lacrimal gland PKC isoforms are differentially localized
and that they translocate differentially in response to phorbol esters and cholinergic agonists.
Received: 25 June 1996/Revised: 24 December 1996 相似文献
14.
Membrane phospholipids represent a potential influence on the enzymatic properties of the Na,K-ATPase. Little is known concerning
the effects of the fatty acid environment surrounding the enzyme on the kinetic properties of the Na,K-ATPase. We used the
most obvious difference among the α isoforms of rat, their affinities for digitalis glycosides, to examine the relationship
between the lipid environment and the Na,K-ATPase. Specific membrane environments that differ in their fatty acid composition
were produced by drug-induced diabetes, as well as variations in diet. The α1 isoforms in various tissues were then characterized
by their resistance to ouabain in Na,K-ATPase-enriched membrane microsomal fractions. The Na,K-ATPase activity in nerves and
hearts were altered by diabetes and partially restored in nerves after a fish oil diet. Evaluation of enzyme kinetics (dose-response
curves for ouabain) in membrane preparations allowed us to correlate the ouabain affinity of α1 isoform with fatty acid composition.
The affinity of the α1 isoform for ouabain was significantly increased with accretions in the total amount of fatty acids
of the n-6 series (P < 0.0001). Our observations provide a partial explanation for the observed difference in isoform properties among tissues.
Moreover, these results underline the interaction between membrane fatty acids and the glycoside binding site of the Na,K-ATPase
α1 subunit.
Received: 15 June 1998/Revised: 18 November 1998 相似文献
15.
Haspel HC Stephenson KN Davies-Hill T El-Barbary A Lobo JF Croxen RL Mougrabi W Koehler-Stec EM Fenstermacher JD Simpson IA 《The Journal of membrane biology》1999,169(1):45-53
Barbiturates inhibit GLUT-1-mediated glucose transport across the blood-brain barrier, in cultured mammalian cells, and in
human erythrocytes. Barbiturates also interact directly with GLUT-1. The hypotheses that this inhibition of glucose transport
is (i) selective, preferring barbiturates over halogenated hydrocarbon inhalation anesthetics, and (ii) specific, favoring
some GLUT-# isoforms over others were tested. Several oxy- and thio-barbiturates inhibited [3H]-2-deoxyglucose uptake by GLUT-1 expressing murine fibroblasts with IC50s of 0.2–2.9 mm. Inhibition of GLUT-1 by barbiturates correlates with their overall lipid solubility and pharmacology, and requires hydrophobic
side chains on the core barbiturate structure. In contrast, several halogenated hydrocarbons and ethanol (all ≤10 mm) do not significantly inhibit glucose transport. The interaction of these three classes of anesthetics with purified GLUT-1
was evaluated by quenching of intrinsic protein fluorescence and displayed similar specificities and characteristics. The
ability of barbiturates to inhibit other facilitative glucose transporters was determined in cell types expressing predominantly
one isoform. Pentobarbital inhibits [3H]-2-deoxyglucose and [14C]-3-O-methyl-glucose uptake in cells expressing GLUT-1, GLUT-2, and GLUT-3 with IC50s of ∼1 mm. In contrast, GLUT-4 expressed in insulin-stimulated rat adipocytes was much less sensitive than the other isoforms to inhibition
by pentobarbital (IC50 of >10 mm). Thus, barbiturates selectively inhibit glucose transport by some, but not all, facilitative glucose transporter isoforms.
Received: 10 November 1998/Revised: 3 February 1999 相似文献
16.
The complete gene of cytosolic malate dehydrogenase (cMDH) from Camellia sinensis, called Cs cMDH, was obtained by RT PCR and rapid amplification of cDNA ends (GenBank accession number GQ845406). This gene was 1 235 bp in length, encoding a protein of 332 amino acids with the putative molecular weight of 355 kD. The Ecoli Rosetta (DE3) harboring pGEX MDH was induced by 05 mmol·L 1 IPTG at 32℃ for 3 hours, and a 615 kD glutathione Stransferase (GST) fused MDH was obtained in soluble form. The results of NCBI BLAST revealed that Cs cMDH shared 88%-93% of amino acid sequence identity with other cMDH from different higher plants. According to the multiple sequence alignment based on the three dimensional structure of protein, Cs cMDH was predicted to be a dimer with thirteen β sheet and thirteen α helix of each subunit. Cs cMDH contains typical fingerprint sequence (G12AAGQIG18) as all MDHs. The amino acid D43 in Cs cMDH is conserved in all NAD MDHs. Cs cMDH also has some conserved sequence units homologous to other NAD MDHs, such as NAD+ binding sites, catalytic motif and substrate binding sites. Moreover, Cs cMDH contains six Cys which are highly conserved in all plant NAD cMDHs. Therefore, Cs cMDH was inferred to be NAD dependent cMDH. The present study may provide the fundament for the further functional characterization of Cs cMDH. 相似文献
17.
Marcellous Le Roux Ethel Phiri Wesaal Khan Muhammet Şakiroğlu Alex Valentine Sehaam Khan 《Journal of plant physiology》2014
During P deficiency, the increased activity of malate dehydrogenase (MDH, EC 1.1.1.37) can lead to malate accumulation. Cytosolic- and nodule-enhanced MDH (cMDH and neMDH, respectively) are known isoforms, which contribute to MDH activity in root nodules. The aim of this study was to investigate the role of the cMDH isoforms in nodule malate supply under P deficiency. Nodulated lupins (Lupinus angustifolius var. Tanjil) were hydroponically grown at adequate P (+P) or low P (−P). Total P concentration in nodules decreased under P deficiency, which coincided with an increase in total MDH activity. A consequence of higher MDH activity was the enhanced accumulation of malate derived from dark CO2 fixation via PEPC and not from pyruvate. Although no measurable neMDH presence could be detected via PCR, gene-specific primers detected two 1 kb amplicons of cMDH, designated LangMDH1 (corresponding to +P, HQ690186) and LangMDH2 (corresponding to −P, HQ690187), respectively. Sequencing analyses of these cMDH amplicons showed them to be 96% identical on an amino acid level. There was a high degree of diversification between proteins detected in this study and other known MDH proteins, particularly those from other leguminous plants. Enhanced malate synthesis in P-deficient nodules was achieved via increased anaplerotic CO2 fixation and subsequent higher MDH activities. Novel isoforms of cytosolic MDH may be involved, as shown by gene expression of specific genes under P deficiency. 相似文献
18.
M.-A. Pou de Crescenzo S. Gallais A. Léon D.L. Laval-Martin 《The Journal of membrane biology》2001,182(2):135-146
Among different treatments assayed, a mix of a nonionic detergent (5% Tween-20) with 0.5 m NaCl was found to solubilize a large part of the calmodulin-dependent NAD+ kinase bound to the inner mitochondrial membrane. It also stimulated its activity by increasing 7 times the maximal velocity.
Activity stimulation was also observed with phosphatidylcholine, phosphatidylethanolamine and with reductants (HSO3 and DTT). This solubilized NAD+ kinase and the calmodulin-dependent cytosoluble isoform displayed distinct molecular masses, as well as different kinetic
parameters. We propose that solubilization of membrane-bound NAD+ kinase could occur in vivo in Avena sativa and could generate a soluble isoform.
Received: 6 November 2000/Revised: 18 April 2001 相似文献
19.
Kirby RR 《Molecular biology and evolution》2000,17(12):1816-1825
Clines in intraspecific genetic variation are frequently associated with an environmental transition. Here, divergence among nucleotide sequences of two nuclear loci, cytosolic and mitochondrial malate dehydrogenase (cMDH and mMDH, respectively), is described, in a multitrait cline over a distance of ca. 3 km where shell phenotype, allozyme, mitochondrial DNA haplotype, and centric fusion (Robertsonian translocations) frequencies covary with temperature and humidity and change abruptly in a continuous population of the dog-whelk (Nucella lapillus), a common intertidal snail of the north temperate Atlantic. Protein electrophoresis has already shown two alleles of mMDH varying from fixation of one allele to near fixation of the other, whereas cMDH appears to be monomorphic. The results of this study show a striking disparity in nucleotide sequence divergence among alleles at the two loci, with extreme molecular differentiation in one of them. Four alleles of cMDH were found to have nucleotide and amino acid sequence divergences of 0.4% and 0.3%, respectively. In contrast, the two mMDH cDNA alleles differed by 23% and 20% at the nucleotide and amino acid levels, respectively. Analysis of a 91-bp partial nucleotide sequence of mMDH from Nucella freycineti, the closest relative of N. lapillus, revealed two similar alleles and indicated that the divergence in mMDH in N. lapillus represents an ancient transpecific polymorphism in these Nucella. Together with earlier studies on variation in N. lapillus, it is argued that the polymorphism in mMDH and the clines in N. lapillus represent the presence of two persistent coadapted gene complexes, multitrait coevolving genetic solutions to environmental variation, which may presently enable this snail to exploit a diverse environment successfully. 相似文献
20.
P. Koulen T. Janowitz F.W. Johenning B.E. Ehrlich 《The Journal of membrane biology》2001,183(3):155-163
Calcium (Ca2+)-mediated signaling is fueled by two sources for Ca2+: Ca2+ can enter through Ca2+ channels located in the plasma membrane and can also be released from intracellular stores. In the present study the intracellular
Ca2+ release channel/ryanodine receptor (RyR) from zebrafish skeletal muscle was characterized. Two RyR isoforms could be identified
using immunoblotting and single-channel recordings. Biophysical properties as well as the regulation by modulators of RyR,
ryanodine, ruthenium red and caffeine, were measured. Comparison with other RyRs showed that the zebrafish RyRs have features
observed with all RyRs described to date and thus, can serve as a model system in future genetic and physiological studies.
However, some differences in the biophysical properties were observed. The slope conductance for both isoforms was higher
than that of the mammalian RyR type 1 (RyR1) measured with divalent ions. Also, inhibition by millimolar Ca2+ concentrations of the RyR isoform that is inhibited by high Ca2+ concentrations (teleost α RyR isoform) was attenuated when compared to mammalian RyRs. Due to the widespread expression of
RyR these findings have important implications for the interpretation of the role of the RyR in Ca2+ signaling when comparing zebrafish with mammalian physiology, especially when analyzing mutations underlying physiological
changes in zebrafish.
Received: 15 February 2001/Revised: 1 June 2001 相似文献