首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 171 毫秒
1.
Mutants of Escherichia coli defective in phosphatidylserine synthetase (pss) make less phosphatidylethanolamine than normal cells, and they are temperature sensitive for growth. We have isolated a new mutant, designated RA2021, which is better than previously available strains in that the residual phosphatidylethanolamine level approaches 25% after 4 h at 42 degrees C. The total amount of phospholipid normalized to the density of the culture is about the same in RA2021 (pss-21) as in the isogenic wild-type RA2000 (pss(+)). Consequently, there is a net accumulation of polyglycerophosphatides in the mutant, particularly of cardiolipin. The addition of 10 to 20 mM MgCl(2) to a culture of RA2021 prolongs growth under nonpermissive conditions and prevents loss of cell viability, but it does not eliminate the temperature-sensitive phenotype. Divalent cations, like Mg(2+), do not correct the phospholipid composition of the mutant, but may act indirectly by balancing the negative charges of phosphatidylglycerol and cardiolipin. To determine the effects of the pss mutation on membrane composition, we have examined the subcellular distribution of the polyglycerophosphatides that accumulate in these strains. All of the excess anionic lipids of RA2021 are associated with the envelope fraction and are distributed equally between the inner and outer membranes. The protein compositions of the isolated membranes do not differ significantly in the mutant and wild type. The fatty acid composition of RA2021 is almost the same as wild type at 30 degrees C, but there is more palmitic and cyclopropane fatty acid at 42 degrees C. These results demonstrate that the modification of the polar lipid composition observed in pss mutants affects both membranes and that cardiolipin, which is not ordinarily present in large quantities, can accumulate in the outer membrane when it is overproduced by the cell. The altered polar headgroup composition of the outer membrane in pss mutants may account, in part, for their hypersensitivity to the aminoglycoside antibiotics.  相似文献   

2.
Mutants of Escherichia coli K-12 defective in CDP-diglyceride:L-serine phosphatidyltransferase (phosphatidylserine synthetase) can be isolated by a rapid autoradiographic screening assay described previously (Raetz, C. R. H. (1975) Proc. Natl. Acad. Sci. U. S. A. 72, 2274-2278). Four organisms of this kind have now been characterized. The gene (designated pss) which is altered in these mutants is closely linked to the nadB locus near minute 49 on the E. coli chromosome. Strains carrying the pss-8 mutation do not grow at elevated temperatures and have low levels of an altered synthetase in cell extracts. An analysis of several hundred transductants and temperature-resistant revertants reveals that the pss-8 mutation is responsible both for the enzyme defect and for the phenotype. When a pss-8 mutant is shifted to the nonpermissive temperature, the cells stop dividing and form long filaments. After 3 hours at 44 degrees the level of phosphatidylethanolamine drops from 66 to 32% (percentage of the total lipid phosphorus), while the combined levels of phosphatidylglycerol and cardiolipin rise from 34 to 68%.  相似文献   

3.
Escherichia coli mutants harboring the pss-1 allele (coding for a temperature-sensitive phosphatidylserine synthase) are temperature sensitive for growth and synthesize less phosphatidylethanolamine at higher temperatures, giving rise to abnormal membrane phospholipid compositions. To obtain information concerning the determinant for the phospholipid polar headgroup composition and the lethal factor in the defective membranes, we have examined the effect of increased supply of sn-glycerol 3-phosphate on the phospholipid synthesis and the growth ability of a pss-1 mutant. For this purpose, a pair of E. coli K-12 derivatives isogenic except for the pss-1 allele was constructed from strain BB26-36 to harbor the mutations related to glycerol metabolism (glpD3, glpR2, glpKi, and phoA8). Pulse- and uniform-labeling of phospholipids with 32P at 42 degrees C in a synthetic medium with (0.2%) or without glycerol showed that glycerol further lowered the temperature-sensitive formation of phosphatidylethanolamine, removed the phosphatidate and CDP-diacylglycerol accumulated in the absence of glycerol, and resulted in an increase in cardiolipin content in the pss-1 mutant. The phospholipid synthesis and contents in the pss+ strain were not significantly affected by glycerol. Glycerol in the medium markedly enhanced the growth defect of the pss-1 mutant, which was remediable by sucrose. The results indicate that the intracellular pool of sn-glycerol 3-phosphate is the limiting factor for acidic phospholipid synthesis in the pss-1 mutant, and cardiolipin unusually accumulated is injurious to the functional E. coli membranes. Possible determinants for the phospholipid composition of the wild-type E. coli cells are also discussed on the basis of the present observations.  相似文献   

4.
The cls gene responsible for cardiolipin synthesis in Escherichia coli K-12 was cloned in a 5-kilobase-pair DNA fragment inserted in a mini-F vector, pML31, and then subcloned into a 2.0-kilobase-pair fragment inserted in pBR322. The initial selection of the gene was accomplished in a cls pss-1 double mutant that had lesions in both cardiolipin and phosphatidylserine synthases and required either the cls or the pss gene product for normal growth at 42 degrees C in a broth medium, NBY, supplemented with 200 mM sucrose. The cloned gene was identified as the cls gene by the recovery and amplification of both cardiolipin and cardiolipin synthase in a cls mutant as well as by the integration of a pBR322 derivative into its genetic locus at 27 min on the chromosome of a polA1 mutant. The maxicell analysis indicated that a protein of molecular weight 46,000 is the gene product. The cls gene is thus most likely the structural gene coding for cardiolipin synthase. Hybrid plasmids of high copy numbers containing the cls gene were growth inhibitory to pss-I mutants under the above selective conditions, whereas they inhibited neither the growth of pss-I mutants at 30 degrees C nor that of pss+ strains at any temperature. Amplification of cardiolipin synthase activity was observed, but was not proportional to the probable gene dosage (the enzyme activity was at most 10 times that in wild-type cells), and cardiolipin synthesis in vivo was at the maximum 1.5 times that in wild-type strains, implying the presence in E. coli cells of a mechanism that avoids cardiolipin overproduction, which is possibly disadvantageous to proper membrane functions.  相似文献   

5.
I Shibuya  C Miyazaki    A Ohta 《Journal of bacteriology》1985,161(3):1086-1092
Escherichia coli K-12 derivatives with a common genetic background carrying, either alone or in combination, the pss-1 allele coding for a temperature-sensitive phosphatidylserine synthase (A. Ohta and I. Shibuya, J. Bacteriol. 132:434-443, 1977) and cls- for a defective cardiolipin synthase (G. Pluschke et al., J. Biol. Chem. 253:5048-5055, 1978) were constructed. The phospholipid polar headgroup compositions of these strains were significantly different from each other depending on their genotypes and growth temperature, whereas other membrane characteristics such as the total phospholipid content, fatty acid composition, membrane protein profile, and lipopolysaccharide content were practically the same, suggesting that the phenotypes of these strains were the direct consequences of abnormalities in membrane phospholipid composition. The cls pss-1 double mutation caused an unusual accumulation of phosphatidylglycerol with an extremely low content of cardiolipin. The cls mutation alone was found to give a growth defect, and its introduction into a pss-1 mutant resulted in an enhanced temperature sensitivity of growth. Addition to a broth medium of a proper concentration of sucrose, NaCl, Mg2+, or Ca2+ allowed the growth of a pss-1 mutant at otherwise nonpermissive temperature, but a pss-1 cls double mutant required the combined addition of sucrose or NaCl and MgCl2 for full growth at 42 degrees C. The possible mechanisms for these physiological consequences of the mutations are discussed on a molecular basis. The remedial effects of culture supplements allowed the pss-1 mutants to grow at 42 degrees C resulting in enhanced abnormalities of membrane phospholipid composition.  相似文献   

6.
A pair of putatively isogenic pss(Ts) and pss+ (phosphatidylserine synthetase structural gene) strains was constructed and analyzed, together with the revertants, for the physiological consequences of cessation of the optimal synthesis of phosphatidylethanolamine (PE). Their in vivo and in vitro abilities to synthetize PE and the growth rates at different temperatures were determined. The rate of PE synthesis by OS2101 pss(Ts) was inversely related to the culture temperature. OS2101 in a low-salt broth medium stopped division and formed filamentous cells with declining viability upon the elevation of culture temperature from 27 to 42 or 44 degrees C, whereas the syntheses of deoxyribonucleic acid, ribonucleic acid, and protein were not affected. Proper concentrations of cations such as Na+, K+, NH4+, and Mg2+ or of sucrose could remedy the division and growth of OS2101 at the restrictive temperature without restoring normal PE synthesis. A remedial effect other than osmotic protection of these effectors and an adaptive regulatory mechanism for PE formation are suggested.  相似文献   

7.
The Bacillus subtilis pss gene encoding phosphatidylserine synthase was cloned by its complementation of the temperature sensitivity of an Escherichia coli pssA1 mutant. Nucleotide sequencing of the clone indicated that the pss gene encodes a polypeptide of 177 amino acid residues (deduced molecular weight of 19,613). This value agreed with the molecular weight of approximately 18,000 observed for the maxicell product. The B. subtilis phosphatidylserine synthase showed 35% amino acid sequence homology to the yeast Saccharomyces cerevisiae phosphatidylserine synthase and had a region with a high degree of local homology to the conserved segments in some phospholipid synthases and amino alcohol phosphotransferases of E. coli and S. cerevisiae, whereas no homology was found with that of the E. coli counterpart. A hydropathy analysis revealed that the B. subtilis synthase is very hydrophobic, in contrast to the hydrophilic E. coli counterpart, consisting of several strongly hydrophobic segments that would span the membrane. A manganese-dependent phosphatidylserine synthase activity, a characteristic of the B. subtilis enzyme, was found exclusively in the membrane fraction of E. coli (pssA1) cells harboring a B. subtilis pss plasmid. Overproduction of the B. subtilis synthase in E. coli cells by a lac promoter system resulted in an unusual increase of phosphatidylethanolamine (up to 93% of the total phospholipids), in contrast to gratuitous overproduction of the E. coli counterpart. This finding suggested that the unusual cytoplasmic localization of the E. coli phosphatidylserine synthase plays a role in the regulation of the phospholipid polar headgroup composition in this organism.  相似文献   

8.
We have isolated three mutants of Escherichia coli which have elevated levels of the phospholipid synthetic enzyme phosphatidylserine synthase. One of these strains carries a mutation, designated pssR1, which maps near minute 84 of the chromosome, distinct from the synthase structural gene (pss) at minute 56. The pssR1 mutation causes selective overproduction of phosphatidylserine synthase, since the levels of six other lipid synthetic enzymes are unaltered. The specific activity of the synthase in crude cell extracts of mutants harboring pssR1 is about five times greater than wild type. The synthase can also be overproduced 10-fold in wild type strains with hybrid ColE1 plasmids carrying the synthase structural gene (pss). A pssR1 mutant harboring such a pss plasmid overproduces the synthase about 50-fold. This multiplicative interaction of pssR1 and cloned pss demonstrates that pssR1 is trans-acting. The synthase has been purified in parallel from pssR1 and pssR+ strains. The pssR1 mutant yields more total synthase protein than pssR+, but the pure enzyme has the same specific activity in both cases. Therefore, pssR1 acts by increasing the amount of the normal protein, not by activating the enzyme. The discovery of pssR shows that there are regulatory loci which control the production of enzymes involved in membrane lipid synthesis.  相似文献   

9.
Z Ge  D E Taylor 《Journal of bacteriology》1997,179(16):4970-4976
The Helicobacter pylori pss gene, coding for phosphatidylserine synthase (PSS), was cloned and sequenced in this study. A polypeptide of 237 amino acids was deduced from the PSS sequence. H. pylori PSS exhibits significant amino acid sequence identity with the PSS proteins found in the archaebacterium Methanococcus jannaschii, the gram-positive bacterium Bacillus subtilis, and the yeast Saccharomyces cerevisiae but none with its Escherichia coli counterpart. Expression of the putative pss gene in maxicells gave rise to a product of approximately 26 kDa, which is in agreement with the predicted molecular mass of 26,617 Da. A manganese-dependent PSS activity was found in the membrane fractions of the E. coli cells overexpressing the H. pylori pss gene product. This result indicates that this enzyme is a membrane-bound protein, a conclusion which is supported by the fact that the PSS protein contains several local hydrophobic segments which could form transmembrane helices. The pss gene was inactivated with a chloramphenicol acetyltransferase cassette on the plasmid. However, an isogenic pss gene-disrupted mutant of H. pylori UA802 could not be obtained, suggesting that this enzyme plays an essential role in the growth of this organism.  相似文献   

10.
Salmonella typhimurium containing specific genes coding for either temperature-sensitive (TS) 3-deoxy-D-manno-octulosonate (KDO) 8-phosphate synthetase or TS cytidine monophosphate-KDO synthetase grow normally when incubated at 30 degrees C and are resistant to C-mediated killing. However, bacteria become avirulent and sensitive to C-mediated killing upon thermal inhibition of TS KDO-8-phosphate synthetase (incubation at 38 degrees C) or TS cytidine monophosphate-KDO synthetase (incubation at 42 degrees C). Such thermal inhibition concurrently causes synthesis of an altered outer membrane which we now show is the site that renders cells susceptible to C-mediated killing. After incubation of cells in serum, the altered outer membrane area contains C9 in a trypsin-resistant state and membrane attack complex (MAC) lesions observable by electron microscopy. Trypsin-resistant C9 and MAC lesions were also observed in the inner membrane fraction from such serum-treated cells. In contrast, little C9 and few MAC lesions were associated with unaltered outer membrane areas present on these same serum treated cells. Control cells, grown at 30 degrees C and treated with serum (1) bound one-fifth as much C9 as was bound to cells incubated at 42 degrees C, (2) contained only a rare MAC lesion in the outer membrane, and (3) no observable MAC lesions in the inner membrane. We conclude that the altered outer membrane area is the site that renders cells susceptible to insertion of the MAC into both the outer and inner membrane resulting in cell death.  相似文献   

11.
The cls gene of Escherichia coli is responsible for the synthesis of a major membrane phospholipid, cardiolipin, and has been proposed to encode cardiolipin synthase. This gene cloned on a pBR322 derivative was disrupted by either insertion of or replacement with a kanamycin-resistant gene followed by exchange with the homologous chromosomal region. The proper genomic disruptions were confirmed by Southern blot hybridization and a transductional linkage analysis. Both types of disruptants had essentially the same properties; cardiolipin synthase activity was not detectable, but the strains grew well, although their growth rates and final culture densities were lower than those of the corresponding wild-type strains and strains with the classical cls-1 mutation. A disruptant harboring a plasmid that carried the intact cls gene grew normally. The results indicate that the cls gene and probably the cardiolipin synthase are dispensable for E. coli but may confer growth or survival advantages. Low but definite levels of cardiolipin were synthesized by all the disruptants. Cardiolipin content of the cls mutants depended on the dosage of the pss gene, and attempts to transfer a null allele of the cls gene into a pss-1 mutant were unsuccessful. We point out the possibilities of minor cardiolipin formation by phosphatidylserine synthase and of the essential nature of cardiolipin for the survival of E. coli cells.  相似文献   

12.
Genes involved in the production of the extracellular (1-->3)-beta-glucan, curdlan, by Agrobacterium sp. strain ATCC 31749 were described previously (Stasinopoulos et al., Glycobiology 9:31-41, 1999). To identify additional curdlan-related genes whose protein products occur in the cell envelope, the transposon TnphoA was used as a specific genetic probe. One mutant was unable to produce high-molecular-mass curdlan when a previously uncharacterized gene, pss(AG), encoding a 30-kDa, membrane-associated phosphatidylserine synthase was disrupted. The membranes of the mutant lacked phosphatidylethanolamine (PE), whereas the phosphatidylcholine (PC) content was unchanged and that of both phosphatidylglycerol and cardiolipin was increased. In the mutant, the continued appearance of PC revealed that its production by this Agrobacterium strain is not solely dependent on PE in a pathway controlled by the Pss(AG) protein at its first step. Moreover, PC can be produced in a medium lacking choline. When the pss(AG)::TnphoA mutation was complemented by the intact pss(AG) gene, both the curdlan deficiency and the phospholipid profile were restored to wild-type, demonstrating a functional relationship between these two characteristics. The effect of the changed phospholipid profile could occur through an alteration in the overall charge distribution on the membrane or a specific requirement for PE for the folding into or maintenance of an active conformation of any or all of the structural proteins involved in curdlan production or transport.  相似文献   

13.
The internalization of fluorescent analogs of phosphatidylserine and phosphatidylethanolamine following their insertion into the plasma membrane of cultured Chinese hamster fibroblasts was examined. When liposomes containing the fluorescent lipid 1,2-(palmitoyl-N-4-nitrobenzo-2-oxa-1,3-diazole-amino-caproyl) phosphatidylserine [palmitoyl-C6-NBD)-PS), were incubated with monolayer cell cultures at 2 degrees C, spontaneous transfer of the fluorescent lipid from the liposomes to the cells occurred, resulting in prominent labeling of the plasma membrane. However, if the cells were washed and warmed to 7 degrees C for 30 min, the (palmitoyl-C6-NBD)-PS also labeled numerous intracellular membranes. Evidence is presented suggesting that this internalization was not due to endocytosis, but was the result of transmembrane movement of the (palmitoyl-C6-NBD)-PS at the plasma membrane followed by translocation of lipid monomers from the plasma membrane to internal membranes. This transmembrane movement was reversibly inhibited by depletion of cellular ATP levels and was blocked by treatment with structural analogs of the lipid or by pretreatment of cells with glutaraldehyde or N-ethyl-maleimide. A fluorescent analog of phosphatidylethanolamine [palmitoyl-C6-NBD)-PE), which also exhibits transmembrane movement at the plasma membrane at 7 degrees C (Sleight, R. G., and Pagano, R. E. (1985) J. Biol. Chem. 260, 1146-1154), was further studied. Its transmembrane movement was also inhibited by depletion of cellular ATP levels, or by pretreatment of cells with N-ethylmaleimide. The transmembrane movement of the fluorescent phosphatidylserine and phosphatidylethanolamine analogs was inhibited when the unnatural D-isomers of these lipids were used, further suggesting that this process was stereospecific and therefore likely to have been protein-mediated.  相似文献   

14.
Temperature-sensitive conditional lethal mutants in phosphatidylserine decarboxylase (psd) accumulate large amounts of phosphatidylserine under nonpermissive conditions (42 degrees C) prior to cell death. In addition, the ratio of cardiolipin to phosphatidylglycerol is increased. At an intermediate temperature (37 degrees C), high levels of phosphatidylserine can be maintained with little effect on cell growth or viability. Under these conditions, both the rate of induction and the function of the lactose transport system are normal. At 42 degrees C addition of Mg2+ or Ca2+ to mutant cultures produces a partial phenotypic suppression. Growth is prolonged and the filaments normally present at 42 degrees C do not form. Upon transfer to the nonpermissive temperature, there is a considerable lag before accumulation of phosphatidylserine begins and the growth rate is affected. Based on the kinetics of heat inactivation of phosphatidylserine decarboxylase activity in extracts, in intact nongrowing cells, and in growing cells, it appears that the enzyme newly synthesized at 42 degrees C is more thermolabile in vivo than enzyme molecules previously inserted into the membrane at the lower temperature. Thus, the older, stable enzymatic activity must be diluted during growth before physiological effects are observed.  相似文献   

15.
Phospholipid metabolism of the microsporidian Encephalitozoon cuniculi, an obligate intracellular parasite, has been investigated. Labeled precursor incorporation experiments have shown that phosphatidylserine decarboxylase and phosphatidylethanolamine N-methyltransferase are more active in cells infected by E. cuniculi than in uninfected cells. In contrast, no difference was observed in the activity of Kennedy pathway's enzymes, the mammalian pathway. This suggests the occurrence in microsporidia of a bacteria- and fungi-typical pathway for phospholipid synthesis, which is supported by the identification of two genes implicated in this pathway, the cds gene encoding the key enzyme CDP-diacylglycerol synthase (E.C. 2.7.7.41) and the pss gene for CDP-alcohol phosphatidyltransferase. The pss gene could encode phosphatidylserine synthase (E.C. 2.7.8.8.), which catalyses the de novo synthesis of phosphatidylserine in bacteria and fungi. The complete CDP-diacylglycerol synthase messenger has been isolated and shows very short 5' and 3' untranslated regions. This is strong evidence for the functionality of a metabolic pathway which could be a potential target against microsporidia which infect humans.  相似文献   

16.
The enzymes of phospholipid synthesis in Clostridium butyricum   总被引:5,自引:0,他引:5  
We have examined extracts of Clostridium butyricum for several enzymes of phospholipid synthesis. Membrane particles were shown to catalyze the formation of CDP-diglyceride from [3H]CTP and phosphatidic acid. The reaction was dependent on Mg2+ and stimulated by monovalent cations. CDP-diglyceride formed in vitro was found to be a substrate for both phosphatidylglycerophosphate synthetase and phosphatidylserine synthetase. The formation of phosphatidylglycerophosphate from added CDP-diglyceride and [U-14C]sn-glycerol-3-phosphate was dependent on Mg2+ and Triton X-100. The dephosphorylation of endogenously-generated phosphatidylglycerophosphate to yield phosphatidylglycerol was observed to be pH-dependent. The formation of phosphatidylserine from CDP-diglyceride and L-[3-14C]serine was stimulated by Mg2+ and Triton X-100. dCDP-diglyceride was a suitable substrate for both phosphatidylglycerophosphate synthetase and phosphatidylserine synthetase. Phosphatidylserine decarboxylase activity was barely detectable in membrane particles from C. butyricum. The addition of E. coli membrane particles provided efficient phosphatidylserine decarboxylase activity in this system. Although plasmalogens are the principal lipids of C. butyricum, none of the products of phospholipid synthesis formed in vitro contained measurable amounts of plasmalogens. The subcellular distribution of both phosphatidylglycerophosphate synthetase and phosphatidylserine synthetase in C. butyricum was also studied. Both were found to be membrane-associated.  相似文献   

17.
Translational fusions between a mutant phoA (lacking its promoter, ribosomal binding site and signal peptide sequence) and Rhizobium 'symbiotic' genes were isolated. Since these fusions expressed alkaline phosphatase (AP), the product of phoA, the genes into which phoA was inserted apparently specify proteins located in the bacterial periplasm or cell membrane, the compartment in which AP has activity. These genes were psiA and genes upstream of psiA (psiA is required for normal nodule development and strains with multicopy psiA fail to make exopolysaccharide (EPS) and to nodulate). Fusions between phoA and pss (exo) genes, which are required for EPS production, also resulted in the expression of AP indicating that products of these pss genes were located at the cell surface. Using gus fusions to psiA and pssA, we found that the former was expressed in N2-fixing bean root nodules but the latter was not.  相似文献   

18.
本文旨在构建阿维链霉菌(Streptomyces avermitilis)来源的磷脂酰丝氨酸合成酶基因(pss)的重组质粒,研究其在毕氏酵母中的异源分泌型表达。利用PCR技术克隆阿维链霉菌来源的pss基因,再通过电转化方法将重组质粒pOG-01转入毕氏酵母KM71中,构建重组工程菌KP1。实验结果表明,阿维链霉菌来源的磷酯酰丝氨酸合成酶基因在毕氏酵母KM71中成功表达,2 mL菌体上清催化50 mmol/L卵磷脂,转酯反应的转化率为58%,酶活为4.83 U/mL。  相似文献   

19.
Intact erythrocytes were spin-labeled with various classes of phospholipid label. The ESR spectrum for phosphatidylcholine spin label was distinctly different from those for phosphatidylserine, phosphatidylethanolamine, phosphatidylglycerol and phosphatidic acid spin labels. The overall splitting for the former (52.5 G) was markedly larger than those for the others (approx. 47 G), suggesting a more rigid phosphatidylcholine bilayer phase and more fluid phosphatidylethanolamine and phosphatidylserine phases in the erythrocyte membrane. Evidence for asymmetric distribution of phospholipids in the membrane was obtained. Spin-labeled phosphatidylcholine incorporated into erythrocytes was reduced immediately by cystein and Fe3+, while the reduction of spin-labeled phosphatidylserine was very slow. The present results therefore suggest asymmetric fluidity in erythrocyte membrane; a more rigid outer layer and a more fluid inner layer. The heterogeneity in the lipid structure was also manifested in the temperature dependence of the fluidity. The overall splitting for phosphatidylcholine spin label showed two inflection points at 18 and 33 degrees C, while that for phosphatidylserine spin label had only one transition at 30 degrees C. When the spin-labeled erythrocytes were hemolyzed, the marked difference in the ESR spectra disappeared, indicating homogenization of the heterogenous fluidity. Mg2+ or Mg2+ + ATP prevented the hemolysis-induced spectral changed. Ca2+ did not prevent the homogenization and acted antagonistically to Mg2+. The heterogeneity preservation by Mg2+ was nullified by trypsin, pronase or N-ethylmaleimide added inside the cell. Some inner proteins may therefore be involved in maintaining the heterogeneous structure. The protecting action of Mg2+ was dependent on hemolysis temperature, starting to decrease at 18 degrees C and vanishing at 40 degrees C. The present study suggests that the heterogeneity in the fluidity of intact erythrocyte membranes arises from interactions between lipids and proteins in the membrane and also from interactions between the membrane constituents and the inner proteins. Concentration of cholesterol in the outer layer may also partly contribute to the heterogeneity.  相似文献   

20.
When cultured in the presence of 600 mM D-mannitol, Escherichia coli K-12 cells synthesized two novel phospholipids. The identities of these compounds are postulated to be phosphatidylmannitol and diphosphatidylmannitol, the sugar alcohol analogs of phosphatidylglycerol and cardiolipin, respectively. The nonacylated glycerol moieties of the normal acidic phospholipids were substituted by D-mannitol. The formation of the analogs was significantly enhanced when strains harboring the pss-1 allele, a temperature-sensitive mutation in phosphatidylserine synthase (Ohta and Shibuya, J. Bacteriol. 132:434-443, 1977), were grown at 42 degrees C, and the accumulation of the analogs was maximum in late stationary phase; more than 90% of the total cellular lipids were these novel phospholipids. Strains with a defective cardiolipin synthase (Pluschke et al., J. Biol. Chem. 253:5048-5055, 1978) failed to form the analog lipids, whereas cells with increased cardiolipin synthase activity due to the presence of a pBR322-derived recombinant plasmid containing the structural gene for cardiolipin synthase produced more mannitol lipids than wild-type strains. These observations and the structures of the analog lipids indicated that cardiolipin synthase participates in the formation of these novel phospholipids. We suggest that reversible alcoholysis and condensation, in addition to low substrate specificity of the enzyme, are the mechanisms involved in this process. Addition to the medium of other straight-chain alditols, D-arabitol, ribitol, xylitol, erythritol, and L-threitol also yielded pairs of novel phospholipids, whereas sorbitol or galactitol produced only one analog in small quantities. These acidic phospholipid analogs have not been reported in any living system. They should be useful in the study of structure-function relationships of phospholipids and in manipulating the structures of various membrane systems.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号