共查询到20条相似文献,搜索用时 46 毫秒
1.
A. Wiese M. Münstermann T. Gutsmann B. Lindner K. Kawahara U. Zähringer U. Seydel 《The Journal of membrane biology》1998,162(2):127-138
We have studied the interaction of the polycationic peptide antibiotic polymyxin B (PMB) with asymmetric planar bilayer membranes
via electrical measurements. The bilayers were of different compositions, including those of the lipid matrices of the outer
membranes of various species of Gram-negative bacteria. One leaflet, representing the bacterial inner leaflet, consisted of
a phospholipid mixture (PL; phosphatidylethanolamine, -glycerol, and diphosphatidylglycerol in a molar ratio of 81:17:2).
The other (outer) leaflet consisted either of lipopolysaccharide (LPS) from deep rough mutants of PMB-sensitive (Escherichia coli F515) or -resistant strains (Proteus mirabilis R45), glycosphingolipid (GSL-1) from Sphingomonas paucimobilis IAM 12576, or phospholipids (phosphatidylglycerol, diphytanoylphosphatidylcholine). In all membrane systems, the addition
of PMB to the outer leaflet led to the induction of current fluctuations due to transient membrane lesions. The minimal PMB
concentration required for the induction of the lesions and their size correlated with the charge of the lipid molecules.
In the membrane system resembling the lipid matrix of a PMB-sensitive strain (F515 LPS/PL), the diameters of the lesions were
large enough (d= 2.4 nm ± 8%) to allow PMB molecules to permeate (self-promoted transport), but in all other systems they were too small.
A comparison of these phenomena with membrane effects induced by detergents (dodecyltriphenylphosphonium bromide, dodecyltrimethylammonium
bromide, sodiumdodecylsulfate) revealed a detergent-like mechanism of the PMB-membrane interaction.
Received: 16 September 1997/Revised: 25 November 1997 相似文献
2.
M. Münstermann A. Wiese K. Brandenburg U. Zähringer L. Brade K. Kawahara U. Seydel 《The Journal of membrane biology》1999,167(3):223-232
Planar asymmetric glycolipid/phospholipid bilayer membranes were used as a reconstitution model of the lipid matrix of the
outer membrane of Gram-negative bacteria to study complement (C) activation by various bacterial surface glycolipids with
the aim of defining the C activation pathway. As glycolipids the lipopolysaccharides of Salmonella enterica serovar Minnesota R mutant strains R595 (Re LPS) and R4 (Rd2 LPS), pentaacyl lipid A from the LPS of the Escherichia coli Re mutant F515, and glycosphingolipid GSL-1 of Sphingomonas paucimobilis IAM 12576 were used. Methylester and carboxyl-reduced derivatives of GSL-1 were used to elucidate the role of the carboxyl
group as common functional group of LPS and GSL-1 for C activation. The formation of lytic pores was monitored via the measurement of changes in membrane current. For all glycolipids we observed a considerable increase in membrane current
soon after addition of whole human serum due to the formation of lytic pores in the membranes. Pore formation was dependent
on the presence of C9, indicating that the observed current changes were due to C activation.
We found that in our reconstitution system of the outer membrane lipid A, Re LPS, and Rd2 LPS activated the classical pathway, the activation being independent of specific anti-LPS antibodies. In contrast, GSL-1
and the methylester derivative of GSL-1 activated the alternative pathway even at the low serum concentrations used in this
study (about 0.2% v/v). Interestingly, the carboxyl reduced GSL-1 activated the classical pathway.
Received: 16 July 1998/Revised: 28 October 1998 相似文献
3.
The mechanism of interaction of the cationic antimicrobial protein (18 kDa), CAP18, with the outer membrane of Gram-negative bacteria was investigated applying transmission electron microscopy and voltage-clamp techniques on artificial planar bilayer membranes. Electron micrographs of bacterial cells exposed to CAP18 showed damage to the outer membrane of the sensitive Escherichia coli strains F515 and ATCC 11775, whereas the membrane of the resistant Proteus mirabilis strain R45 remained intact. Electrical measurements on various planar asymmetric bilayer membranes, one side consisting of a phospholipid mixture and the other of different phospholipids or of lipopolysaccharide (reconstitution model of the outer membrane), yielded information about the influence of CAP18 on membrane integrity. Addition of CAP18 to the side with the varying lipid composition led to lipid-specific adsorption of CAP18 and subsequent induction of current fluctuations due to the formation of transient membrane lesions at a lipid-specific clamp voltage. We propose that the applied clamp voltage leads to reorientation of CAP18 molecules adsorbed to the bilayer into an active transmembrane configuration, allowing the formation of lesions by multimeric clustering. 相似文献
4.
In studies of Pseudomonas putida IH-2000, a toluene-tolerant microorganism, membrane vesicles (MVs) were found to be released from the outer membrane when toluene was added to the culture. These MVs were found to be composed of phospholipids, lipopolysaccharides (LPS), and very low amounts of outer membrane proteins. The MVs also contained a higher concentration of toluene molecules (0.172 +/- 0. 012 mol/mol of lipid) than that found in the cell membrane. In contrast to the wild-type strain, the toluene-sensitive mutant strain 32, which differs from the parent strain in LPS and outer membrane proteins, did not release MVs from the outer membrane. The toluene molecules adhering to the outer membrane are eliminated by the shedding of MVs, and this system appears to serve as an important part of the toluene tolerance system of IH-2000. 相似文献
5.
Three gap junctional proteins have been identified in canine ventricular myocytes: connexin 43 (Cx43), connexin 45 (Cx45),
and connexin 40 (Cx40). We have characterized the functional properties of canine Cx45 and examined how Cx45 functionally
interacts with Cx43 in Xenopus oocyte pairs. Homotypic pairs expressing Cx45 were well coupled. Heterotypic pairs composed of Cx45 paired with either Cx43
or Cx38 also developed high levels of conductance. Junctional currents in the heterotypic pairs displayed a highly asymmetrical
voltage dependence. The kinetics and steady-state voltage dependence of the heterotypic channels more closely resembled those
of the Cx45 channels when the Cx45 cRNA-injected cell was relatively negative suggesting that the Cx45 connexon closes for
relative negativity at the cytoplasmic end of the channel. We also show that homotypic and heterotypic channels composed of
Cx45 and Cx43 exhibit differences in pH
i
sensitivity.
Received: 18 August 1995/Revised: 21 November 1995 相似文献
6.
Levi V Rossi JP Echarte MM Castello PR González Flecha FL 《The Journal of membrane biology》2000,173(3):215-225
Thermal stability of plasma membrane Ca2+ pump was systematically studied in three micellar systems of different composition, and related with the interactions amphiphile-protein
measured by fluorescence resonance energy transfer. Thermal denaturation was characterized as an irreversible process that
is well described by a first order kinetic with an activation energy of 222 ± 12 kJ/mol in the range 33–45°C. Upon increasing
the mole fraction of phospholipid in the mixed micelles where the Ca2+ pump was reconstituted, the kinetic coefficient for the inactivation process diminished until it reached a constant value,
different for each phospholipid species. We propose a model in which thermal stability of the pump depends on the composition
of the amphiphile monolayer directly in contact with the transmembrane protein surface. Application of this model shows that
the maximal pump stability is attained when 80% of this surface is covered by phospholipids. This analysis provides an indirect
measure of the relative affinity phospholipid/detergent for the hydrophobic transmembrane surface of the protein (K
LD
) showing that those phospholipids with higher affinity provide greater stability to the Ca2+ pump. We developed a method for directly measure K
LD
by using fluorescence resonance energy transfer from the membrane protein tryptophan residues to a pyrene-labeled phospholipid.
K
LD
values obtained by this procedure agree with those obtained from the model, providing a strong evidence to support its validity.
Received: 5 August 1999/Revised: 20 October 1999 相似文献
7.
This paper presents experimental evidence that an aromatic compound that has a quadrupole moment locates in a polar headgroup
region in the lipid membranes, but not in a membrane interior hydrophobic region, and discusses correlation to the site of
action of benzocaine and butamben on sodium channels. The 2H NMR spectra of benzocaine-d4, benzocaine-d5, butamben-d4, and butamben-d9 in the model membranes were observed. The 2H NMR spectra of perdeuterated palmitic acid and selectively deuterated palmitic acids at C2, C3, C5, C6, C9, or C10, which
were inserted into the lipid membranes, were also observed. The phosphatidylserine (PS), phosphatidylcholine (PC), and liquid
mixtures composed of PS, PC, and phosphatidylethanolamine (PE), which contain or do not contain cholesterol, were employed.
A moment analysis was applied to the 2H NMR spectra of palmitic-d31 acid. An order parameter, S
CD
, for each carbon segment was calculated from the observed quadruple splitting. We concluded that in the lipid mixture containing
cholesterol, the aromatic rings of benzocaine and butamben locate around the glycerol moiety of the lipids and that when there
exists no cholesterol, they locate a little more inside from the headgroup region, directing, in both cases, their amino groups
upward (polar region) and the ethyl and butyl groups downward (hydrophobic region). These data cast a question on the site
of action of the neutral local anesthetics in the sodium channels.
Received: 22 March 2000/Revised: 20 June 2000 相似文献
8.
V. Calderón A. Lázaro R.G. Contreras L. Shoshani C. Flores-Maldonado L. González-Mariscal G. Zampighi M. Cereijido 《The Journal of membrane biology》1998,164(1):59-69
Tight junctions (TJs) are cell-to-cell contacts made of strands, which appear as ridges on P faces and complementary furrows
on E faces on freeze fracture replicas. Evidences and opinions on whether these strands are composed of either membrane-bound
proteins or lipid micelles are somewhat varied. In the present work we alter the lipid composition of Madin-Darby canine kidney
monolayers using a novel approach, while studying (i) their transepithelial electrical resistance, a parameter that depends
on the degree of sealing of the TJs; (ii) the apical-to-basolateral flux of 4 kD fluorescent dextran (JDEX), that reflects the permeability of the intercellular spaces; (iii) the ability of TJs to restrict apical-to-basolateral
diffusion of membrane lipids; and (iv) the pattern of distribution of endogenous and transfected occludin, the sole membrane
protein presently known to form part of the TJs. We show that changing the total composition of phospholipids, sphingolipids,
cholesterol and the content of fatty acids, does not alter TER nor the structure of the strands. Interestingly, enrichment
with linoleic acid increases the JDEX by 631%. The fact that this increase is not reflected in a decrease of TER, suggests that junctional strands do not act as
simple resistive elements but may contain mobile translocating mechanisms.
Received: 7 November 1997/Revised: 20 March 1998 相似文献
9.
We harvested canalicular-enriched plasma membranes of hepatocytes and collected fistula bile from male rats and isolated
the sphingomyelins. Following sphingomyelinase hydrolysis, we identified the sphingomyelin molecular species on the basis
of their benzoylated ceramide derivatives employing high performance liquid chromatography. Sphingomyelin constitutes ≤3%
of total biliary phospholipids (which are mostly sn-1 16:0 long-chain phosphatidylcholines) and approximately 30% of canalicular-enriched
membranes. In both cases, the principal molecular species were composed of 16:0, 18:0, 20:0, 22:0, 23:0, 24:0, 24:1 and 24:2
fatty acid classes. However, the 16:0 fatty acid species was enriched in biliary sphingomyelin to a significantly greater
degree than in sphingomyelins of canalicular-enriched plasma membranes (46% vs. 25% of total). We argue a physical-chemical case for laterally separated domains of very long chain sphingomyelins on the
exoplasmic leaflet of the canalicular membrane. We bolster our hypothesis by the likelihood that the least hydrophobic, e.g.,
16:0 sphingomyelin molecular species, are miscible with biliary phosphatidylcholines, and are secreted into bile. Laterally
separated domains of very long chain sphingomyelins on the exoplasmic leaflet of the canalicular membrane could provide a
means of sequestering cholesterol molecules prior to secretion into bile.
Received: 19 March 1998/Revised: 8 October 1998 相似文献
10.
Boron enters plant roots as undissociated boric acid (H3BO3). Significant differences in B uptake are frequently observed even when plants are grown under identical conditions. It has
been theorized that these differences reflect species differences in permeability coefficient of H3BO3 across plasma membrane. The permeability coefficient of boric acid however, has not been experimentally determined across
any artificial or plant membrane. In the experiments described here the permeability coefficient of boric acid in liposomes
made of phosphatidylcholine was 4.9 × 10−6 cm sec−1, which is in good agreement with the theoretical value. The permeability coefficient varied from 7 × 10−6 to 9.5 × 10−9 cm sec−1 with changes in sterols (cholesterol), the type of phospholipid head group, the length of the fatty acyl chain, and the pH
of the medium. In this study we also used Arabidopsis thaliana mutants which differ in lipid composition to study the effect of lipid composition on B uptake. The chs1-1 mutant which has lower proportion of sterols shows 30% higher B uptake compared with the wild type, while the act1-1 mutant which has an increased percentage of longer fatty acids, exhibited 35% lower uptake than the wild type. Lipid composition
changes in each of the remaining mutants influenced B uptake to various extents. These data suggest that lipid composition
of the plasma membrane can affect total B uptake.
Received: 15 October 1999/Revised: 11 February 2000 相似文献
11.
VDAC forms the major pathway for metabolites across the mitochondrial outer membrane. The regulation of the gating of VDAC
channels is an effective way to control the flow of metabolites into and out of mitochondria. Here we present evidence that
actin can modulate the gating process of Neurospora crassa VDAC reconstituted into membranes made with phosphatidylcholine. An actin concentration as low as 50 nm caused the VDAC-mediated membrane conductance to drop by as much as 85% at elevated membrane potentials. Actin's effect could
be quickly reversed by adding pronase to digest the protein. α-Actin, from mammalian muscle, has a stronger effect than β-
and γ-actin from human platelets. The monomeric form of actin, G-actin, is effective. Stabilization of the fibrous form, F-actin,
with the mushroom toxin, phalloidin, blocks the effect of actin on VDAC, indicating that F-actin might be ineffective. Cytochalasin
B did not interfere with the ability of actin to favor VDAC closure. DNase-I did effectively block actin's effect on VDAC,
and VDAC decreased actin's inhibitory effect on DNase-I activity, indicating that N. crassa VDAC competes with DNase-I for the same binding site on actin. The actin-VDAC interaction might be a mechanism by which actin
regulates energy metabolism.
Received: 28 August 2000/Revised: 1 December 2000 相似文献
12.
Calcium-induced fusion of liposomes was studied with a view to understand the role of membrane tension in this process. Lipid
mixing due to fusion was monitored by following fluorescence of rhodamine-phosphatidyl-ethanolamine incorporated into liposomal
membrane at a self-quenching concentration. The extent of lipid mixing was found to depend on the rate of calcium addition:
at slow rates it was significantly lower than when calcium was injected instantly. The vesicle inner volume was then made
accessible to external calcium by adding calcium ionophore A23187. No effect on fusion was observed at high rates of calcium
addition while at slow rates lipid mixing was eliminated. Fusion of labeled vesicles with a planar phospholipid membrane (BLM)
was studied using fluorescence microscopy. Above a threshold concentration specific for each ion, Ca2+, Mg2+, Cd2+ and La3+ induce fusion of both charged and neutral membranes. The threshold calcium concentration required for fusion was found to
be dependent on the vesicle charge, but not on the BLM charge. Pretreatment of vesicles with ionophore and calcium inhibited
vesicle fusion with BLM. This effect was reversible: chelation of calcium prior to the application of vesicle to BLM completely
restored their ability to fuse. These results support the hypothesis that tension in the outer monolayer of lipid vesicle
is a primary reason for membrane destabilization promoting membrane fusion. How this may be a common mechanism for both purely
lipidic and protein-mediated membrane fusion is discussed.
Received: 27 September 1999/Revised: 22 March 2000 相似文献
13.
In our study we investigated hemispherical phospholipid bilayer membranes and phospholipid vesicles made from hexadecaprenyl
monophosphate (C80-P), dioleoylphosphatidylocholine (DOPC) and their mixtures by voltammetric and transmission electron microscopy (TEM) techniques.
The current-voltage characteristics, the membrane conductance-temperature relationships and the membrane breakdown voltage
have been measured for different mixtures of C80-P/DOPC. The membrane hydrophobic thickness and the activation energy of ion migration across the membrane have been determined.
Hexadecaprenyl monophosphate decreased in comparison with DOPC bilayers, the membrane conductance, increased the activation
energy and the membrane breakdown voltage for the various value of C80-P/DOPC mole ratio, respectively. The TEM micrographs of C80-P, DOPC and C80-P/DOPC lipid vesicles showed several characteristic structures, which have been described. The data indicate that hexadecaprenyl
monophosphate modulates the surface curvature of the membranes by the formation of aggregates in liquid-crystalline phospholipid
membranes. We suggest that the dynamics and conformation of hexadecaprenyl monophosphate in membranes depend on the transmembrane
electrical potential. The electron micrographs indicate that polyprenyl monophosphates with single isoprenyl chains form lipid
vesicular bilayers. The thickness of the bilayer, evaluated from the micrographs, was 11 ± 1 nm. This property creates possibility
of forming primitive bilayer lipid membranes by long single-chain polyprenyl phosphates in abiotic conditions. It can be the
next step in understanding the origin of protocells.
Received: 10 January 2000/Revised: 7 June 2000 相似文献
14.
Prenner E Sommer A Maurer N Glatter O Gorges R Paltauf F Hermetter A 《The Journal of membrane biology》2000,174(3):237-243
Choline phospholipids are the major constituents of the outer layer of the erythrocyte membrane. To investigate their lateral
membrane organization we determined the fluorescence lifetime properties of diphenylhexatriene analogues of phosphatidylcholine,
choline plasmalogen, (the respective enolether derivative), and sphingomyelin inserted into the outer layer of hemoglobin-free
ghosts. Fluorescence lifetimes were recorded by time-resolved phase and modulation fluorometry and analyzed in terms of Continuous
Lorentzian distributions. To assess the influence of membrane proteins on the fluorescence lifetime of the labeled lipids
in the biomembrane, lipid vesicles were used as controls. In general, the lifetime distributions in the ghost membranes are
broad compared to vesicles. Phosphatidylcholine and sphingomyelin exhibit very similar lifetime distributions in contrast
to an increased plasmalogen lifetime heterogeneity in both systems. Orientational effects of side chain mobilities on the
observed lifetimes can be excluded. Fluorescence anisotropies revealed identical values for all three labeled phospholipids
in the biomembrane.
Received: 22 July 1999/Revised: 6 January 2000 相似文献
15.
Vié V Van Mau N Pomarède P Dance C Schwartz JL Laprade R Frutos R Rang C Masson L Heitz F Le Grimellec C 《The Journal of membrane biology》2001,180(3):195-203
After activation, Bacillus thuringiensis (Bt) insecticidal toxin forms pores in larval midgut epithelial cell membranes, leading to host death. Although the crystal
structure of the soluble form of Cry1Aa has been determined, the conformation of the pores and the mechanism of toxin interaction
with and insertion into membranes are still not clear. Here we show that Cry1Aa spontaneously inserts into lipid mono- and
bilayer membranes of appropriate compositions. Fourier Transform InfraRed spectroscopy (FTIR) indicates that insertion is
accompanied by conformational changes characterized mainly by an unfolding of the β-sheet domains. Moreover, Atomic Force
Microscopy (AFM) imaging strongly suggests that the pores are composed of four subunits surrounding a 1.5 nm diameter central
depression.
Received: 14 July 2000/Revised: 28 December 2000 相似文献
16.
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
17.
Scott RH Whyment AD Foster A Gordon KH Milne BF Jaspars M 《The Journal of membrane biology》2000,176(2):119-131
We have chemically characterized a preparation of halitoxins, (1,3 alkyl-pyridinium salts) isolated from the marine sponge
Callyspongia ridleyi. At concentrations of 50 and 5 μg/ml the halitoxin preparation caused irreversible membrane potential depolarization, decreased
input resistance and inhibited evoked action potentials when applied to cultured dorsal root ganglion neurones. Under whole
cell voltage clamp the halitoxins produced an increase in cation conductance that was attenuated by replacing sodium with
N-methyl-d-glucamine. Fura-2 fluorescence ratiometric calcium imaging was used to directly measure calcium flux into neurones after
exposure to halitoxins. Calcium influx, evoked by the halitoxins, persisted when the neurones were bathed in medium containing
the voltage-activated calcium channel antagonists cadmium and nickel. Experiments on undifferentiated F-11 cells showed little
or no calcium influx in response to depolarizing concentrations of potassium and indicated that halitoxins evoked massive
calcium influx in the absence of voltage-activated calcium channels. The halitoxins also produced transient increases in intracellular
calcium when F-11 cells were bathed in calcium-free medium suggesting that the toxins could release calcium from intracellular
stores. The pore-forming action of the halitoxins was identified when the toxins were applied to artificial lipid bilayers
composed of phosphatidylcholine and cholesterol. Halitoxins evoked channel-like activity in the lipid bilayers, with estimated
unitary conductances of between 145pS and 2280pS, possibly indicating that distinct channels could be produced by the different
components in the preparation of halitoxins.
Received: 23 December 1999/Revised: 3 April 2000 相似文献
18.
The gram-positive bacterium Mycobacterium phlei was treated with detergents. Reconstitution experiments using lipid bilayers suggested that the detergent extracts contain
a channel forming protein. The protein was purified to homogeneity by preparative SDS-PAGE and identified as a protein with
an apparent molecular mass of about 135 kDa. The channel-forming unit dissociated into subunits with a molecular mass of about
22 kDa when it was boiled in 80% dimethylsulfoxid (DMSO). The channel has on average a single channel conductance of 4.5 nS
in 1 m KCl and is highly voltage-dependent in an asymmetric fashion when the protein is added to only one side of the membrane.
Zero-current membrane potential measurements with different salts implied that the channel is highly cation-selective because
of negative point charges in or near the channel mouth. Analysis of the single-channel conductance as a function of the hydrated
cation radii using the Renkin correction factor and the effect of the negative point charges on the single-channel conductance
suggest that the diameter of the cell wall channel is about 1.8 to 2.0 nm. The channel properties were compared with those
of other members of the mycolata and suggest that these channels share common features. Southern blots demonstrated that the
chromosome of M. phlei and other mycolata tested contain homologous sequences to mspA (gene of the cell wall porin of Mycobacterium smegmatis).
Received: 22 December 2000/Revised: 10 April 2001 相似文献
19.
R.J. Bick L.M. Buja W.B. Van Winkle G.E. Taffet 《The Journal of membrane biology》1998,164(2):169-175
Cardiac sarcoplasmic reticulum (CSR), isolated from dog hearts, was shown to be asymmetric in the distribution of phospholipids
across the CSR bilayer. Phosphatidylethanolamine was mostly resident in the outer leaflet, phosphatidylcholine was equally
distributed across both monolayers and phosphatidylserine was found primarily in the inner monolayer. This distribution of
headgroups is similar to that found in fast skeletal muscle sarcoplasmic reticulum (SSR); however, the asymmetry in CSR is
not as striking as that in SSR.
Phospholipids retained by the CSR calcium pump protein (CaATPase) after detergent ``stripping' were similar to those intimate
to the SSR CaATPase, although the percentages of unsaturated phospholipids and plasmalogenic phospholipids are not as great
as in the skeletal system. Lipids associated with the CSR CaATPase following DFDNB cross-linking showed a preference for retention
of the aminophospholipids, again similar to the SSR CaATPase. Because the nonrandom distribution of membrane lipids modifies
SSR function, it is likely these membrane lipids impact in situ the function of the CSR.
Received: 19 December 1997/Revised: 3 April 1998 相似文献
20.
One of the most remarkable biochemical differences between the members of two domains Archaea and Bacteria is the stereochemistry
of the glycerophosphate backbone of phospholipids, which are exclusively opposite. The enzyme responsible to the formation
of Archaea-specific glycerophosphate was found to be NAD(P)-linked sn-glycerol-1-phosphate (G-1-P) dehydrogenase and it was first purified from Methanobacterium thermoautotrophicum cells and its gene was cloned. This structure gene named egsA (enantiomeric glycerophosphate synthase) consisted of 1,041 bp and coded the enzyme with 347 amino acid residues. The amino
acid sequence deduced from the base sequence of the cloned gene (egsA) did not share any sequence similarity except for NAD-binding region with that of NAD(P)-linked sn-glycerol-3-phosphate (G-3-P) dehydrogenase of Escherichia coli which catalyzes the formation of G-3-P backbone of bacterial phospholipids, while the deduced protein sequence of the enzyme
revealed some similarity with bacterial glycerol dehydrogenases. Because G-1-P dehydrogenase and G-3-P dehydrogenase would
originate from different ancestor enzymes and it would be almost impossible to interchange stereospecificity of the enzymes,
it seems likely that the stereostructure of membrane phospholipids of a cell must be maintained from the time of birth of
the first cell. We propose here the hypothesis that Archaea and Bacteria were differentiated by the occurrence of cells enclosed
by membranes of phospholipids with G-1-P and G-3-P as a backbone, respectively.
Received: 24 March 1997 / Accepted: 21 May 1997 相似文献