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1.
Zhong Li Ruo-Wei Chen Heng-Yi Lei Zhong Shan Tao Bai Qiang Yu Hua-Liang Li 《World journal of microbiology & biotechnology》2009,25(5):745-752
We studied a novel bioflocculant, PX, that is produced from Bacillus Bacillus circulans X3, and has excellent flocculating activity with regard to its characterization and flocculating properties. The bioflocculant
was purified from supernatant by ethanol precipitation, dialysis and gel permeation chromatography (GPC). The major component
of PX was an acid polysaccharide including uronic (19.8%), pyruvic (6.5%) and acetic acids (0.7%). It consisted of galactose,
mannose, xylitol, rhamnose and galacturonic acid in an approximate molar ration of 5:4.1:3:2:1.2. The molecular weight of
PX was about 4.85 × 104 Da as determined by GPC. The infrared spectrum of the bioflocculant indicated the presence of carboxyl, hydroxyl, amino and
methoxyl groups. Studies of the flocculating properties revealed that it was stable at 60–100°C and pH 4–10. Moreover, it
could flocculate a kaolin suspension over a wide range of pH and temperature in the presence of CaCl2. 相似文献
2.
Summary Xylanase from Scytalidium thermophilum was immobilized on Eudragit L-100, a pH sensitive copolymer of methacrylic acid and methyl methacrylate. The enzyme was non-covalently
immobilized and the system expressed 70% xylanase activity. The immobilized preparation had broader optimum temperature of
activity between 55 and 65 °C as compared to 65 °C in case of free enzyme and broader optimum pH between 6.0 and 7.0 as compared
to 6.5 in case of free enzyme. Immobilization increased the t1/2 of enzyme at 60 °C from 15 to 30 min with a stabilization factor of 2. The Km and Vmax values for the immobilized and free xylanase were 0.5% xylan and 0.89 μmol/ml/min and 0.35% xylan and 1.01 μmol/ml/min respectively. An Arrhenius plot showed an increased value of activation energy for immobilized xylanase (227 kcal/mol)
as compared to free xylanase (210 kcal/mol) confirming the higher temperature stability of the free enzyme. Enzymatic saccharification
of xylan was also improved by xylanase immobilization. 相似文献
3.
Cytochrome a
1
c
1 was highly purified from Nitrobacter agilis. The cytochrome contained heme a and heme c of equimolar amount, and its reduced form showed absorption peaks at 587, 550, 521, 434 and 416 nm. Molecular weight per heme a of the cytochrome was estimated to be approx. 100,000–130,000 from the amino acid composition. A similar value was obtained by determining the protein content per heme a. The cytochrome molecule was composed of three subunits with molecular weights of 55,000, 29,000 and 19,000, respectively. The 29 kd subunit had heme c.Hemes a and c of cytochrome a
1
c
1 were reduced on addition of nitrite, and the reduced cytochrome was hardly autoxidizable. Exogenously added horse heart cytochrome c was reduced by nitrite in the presence of cytochrome a
1
c
1; K
m values of cytochrome a
1
c
1 for nitrite and N. agilis cytochrome c were 0.5 mM and and 6 M, respectively. V
max was 1.7 mol ferricytochrome c reduced/min·mol of cytochrome a
1
c
1 The pH optimum of the reaction was about 8. The nitrite-cytochrome c reduction catalyzed by cytochrome a
1
c
1 was 61% and 88% inhibited by 44M azide and cyanide, respectively. In the presence of 4.4 mM nitrate, the reaction was 89% inhibited. The nitrite-cytochrome c reduction catalysed by cytochrome a
1
c
1 was 2.5-fold stimulated by 4.5 mM manganous chloride. An activating factor which was present in the crude enzyme preparation stimulated the reaction by 2.8-fold, and presence of both the factor and manganous ion activated the reaction by 7-fold.Cytochrome a
1
c
1 showed also cytochrome c-nitrate reductase activity. The pH optimum of the reaction was about 6. The nitrate reductase activity was also stimulated by manganous ions and the activating factor. 相似文献
4.
Alan A. DiSpirito Andrew K. Shiemke Sean W. Jordan James A. Zahn Cinder L. Krema 《Archives of microbiology》1994,161(3):258-265
A cytochrome aa
3-type oxidase was isolated with and without a c-type cytochrome (cytochrome c-557) from Methylococcus capsulatus Bath by ion-exchange and hydrophobic chromatography in the presence of Triton X-100. Although cytochrome c-557 was not a constitutive component of the terminal oxidase, the cytochrome c ascorbate-TMPD oxidase activity of the enzyme decreased dramatically when the ratio of cytochrome c-557 to heme a dropped below 1:3. On denaturing gels, the purified enzyme dissociated into three subunits with molecular weights of 46,000, 28,000 and 20,000. The enzyme contains two heme groups (a and a
3), absorption maximum at 422 nm in the resting state, at 445 and 601 nm in the dithionite reduced form and at 434 and 598 nm in the dithionite reduced plus CO form. Denaturing gels of the cytochrome aa
3-cytochrome c-557 complex showed the polypeptides associated with cytochrome aa
3 plus a heme c-staining subunit with a molecular weight of 37,000. The complex contains approximately two heme a, one heme c, absorption maximum at 420 nm in the resting state and at 421, 445, 522, 557 and 601 nm in the dithionite reduced form. The specific activity of the purified enzyme was 130 mol O2/min · mol heme a compared to 753 mol O2/min · mol heme a when isolated with cytochrome c-557.Abbreviations MMO
methan monooxygenase
- sMMO
soluble methane monooxygenase
- pMMO
particulate methane monooxygenase
- TMPD
N,N,N,N-tetramethyl-p-phenylenediamine dihydrochloride
- Na2EDTA
disodium ethylenediamine-tetraacetic acid 相似文献
5.
The effects of phosphorus, Zn2+, CO2, and light intensity on growth, biochemical composition, and the activity of extracellular carbonic anhydrase (CA) in Isochrysis galbana were investigated. A significant change was observed when the concentration of phosphorus in the medium was increased from
5 μmol/L to 1000 μmol/L affecting I. galbana’s cell density, biochemical composition, and the activity of extracellular CA. Phosphorous concentration of 50 μmol/L to 500
μmol/L was optimal for this microalgae. The Zn2+ concentration at 10 μmol/L was essential to maintain optimal growth of the cells, but a higher concentration of Zn2+ (≥ 1000 μmol/L) inhibited the growth of I. galbana. High CO2 concentrations (43.75 mL/L) significantly increased the cell densities compared to low CO2 concentrations (0.35 mL/L). However, the activity of extracellular CA decreased significantly with an increasing concentration
of CO2. The activity of extracellular CA at a CO2 concentration of 43.75 mL/L was approximately 1/6 of the activity when the CO2 concentration was at 0.35 mL/L CO2. Light intensity from 4.0 mW/cm2 to 5.6 mW/cm2 was beneficial for the growth, biochemical composition and the activity of extracellular CA. The lower and higher light intensity
was restrictive for growth and changed its biochemical composition and the activity of extracellular CA. These results indicate
that phosphorus, Zn2+, CO2, and light intensity are important factors that impact growth, biochemical composition and the activity of extracellular
CA in I. galbana. 相似文献
6.
Petronio Pasquali Mauro Degli Esposti Laura Landi Luciana Cabrini Giorgio Lenaz 《Journal of bioenergetics and biomembranes》1985,17(5):283-294
Depletion of endogenous ubiquinone by pentane extraction of mitochondrial membranes lowered succinate-ferricyanide reductase activity, whereas quinone reincorporation restored the enzymatic activity as well as antimycin sensitivity. The oxidant-induced cytochromeb extrareduction, normally found upon ferricyanide pulse in intact mitochondria in the presence of antimycin, was lost in ubiquinone-depleted membranes, even if cytochromec was added. Readdition of ubiquinone-2 restored the oxidant-induced extrareduction with an apparent half saturation at 1 mol/molbc
1 complex saturating at about 5 mol/mol. These findings demonstrate a requirement for the ubiquinone pool of the cytochromeb extrareduction. Since the initial rates of cytochromeb reoxidation upon ferricyanide addition, in the presence of antimycin, did not saturate by any ferricyanide concentration in ubiquinone-depleted mitochondria, a direct chemical reaction between ferricyanide and reduced cytochromeb was postulated. The fact that such direct reaction is much faster in ubiquinone-depleted mitochondria may explain the lower antimycin sensitivity of the succinate ferricyanide reductase activity after removal of endogenous ubiquinone. 相似文献
7.
The distribution of the F420-reactive and F420-nonreactive hydrogenases from the methylotrophic Methanosarcina strain Gö1 indicated a membrane association of the F420-nonreactive enzyme. The membrane-bound F420-nonreactive hydrogenase was purified 42-fold to electrophoretic homogeneity with a yield of 26.7%. The enzyme had a specific activity of 359 mol H2 oxidized · min-1 · mg protein-1. The purification procedure involved dispersion of the membrane fraction with the detergent Chaps followed by anion exchange, hydrophobic and hydroxylapatite chromatography. The aerobically prepared enzyme had to be reactivated anaerobically. Maximal activity was observed at 80°C. The molecular mass as determined by native gel electrophoresis and gel filtration was 77000 and 79000, respectively. SDS gel electrophoresis revealed two polypeptides with molecular masses of 60000 and 40000 indicating a 1:1 stoichiometry. The purified enzyme contained 13.3 mol S2-, 15.1 mol Fe and 0.8 mol Ni/mol enzyme. Flavins were not detected. The amino acid sequence of the N-termini of the subunits showed a higher degree of homology to cubacterial uptake-hydrogenases than to F420-dependent hydrogenases from other methanogenic bacteria. The physiological function of the F420-nonreactive hydrogenase from Methanosarcina strain Gö1 is discussed.Abbreviations
transmembrane electrochemical gradient of H-
- CoM-SH
2-mercaptoethanesulfonate
- F420
(N-l-lactyl--l-glutamyl)-l-glutamic acid phospodiester of 7,8-didemethyl-8-hydroxy-5-deazariboflavin-5-phosphate
- F420H2
reduced F420
- HTP-SH
7-mercaptoheptanoylthreonine phosphate
-
Mb.
Methanobacterium
- PMSF
phenylmethyl-sulfonylfluoride
- Cl3AcOH
trichloroacetic acid 相似文献
8.
以紫斑牡丹种子为试验材料,研究不同浓度的赤霉素(GA_3)处理对种子生根以及生根过程中营养物质、酶活性和内源激素水平变化的影响,为探讨紫斑牡丹种子萌发机制提供依据。结果表明:(1)GA_3处理能够促进种子生根,并以300 mg/L GA_3处理对种子生根效果最好,与对照相比可提前14.67 d生根,生根率可达71.00%。(2)与对照相比,GA_3处理可以在0~15 d时促进种子淀粉水解和可溶性糖的积累,并加速可溶性蛋白的消耗,在0~30 d促进过氧化物酶(POD)活性的提高,从而促进种子萌发生根。(3)在种子沙藏生根过程中,种子脱落酸(ABA)含量呈下降趋势,赤霉素(GA)、玉米素核苷(ZR)和吲哚乙酸(IAA)含量均表现出先上升后下降的趋势,与对照相比,GA_3处理可使种子GA、ZR和IAA的含量在沙藏前期明显上升,以解除种子休眠。研究发现,外源GA_3处理可以调控紫斑牡丹种子内源激素含量和POD活性的变化,促进营养物质转化,从而提前解除种子休眠使其萌发。 相似文献
9.
During growth of Acetobacterium woodii on fructose, glucose or lactate in a medium containing less than 0.04% bicarbonate, molecular hydrogen was evolved up to 0.1 mol per mol of substrate. Under an H2-atmosphere growth of A. woodii with organic substrates was completely inhibited whereas under an H2/CO2-atmosphere rapid growth occurred. Under these conditions H2+CO2 and the organic substrate were utilized simultaneously indicating that A. woodii was able to grow mixotrophically.
Clostridium aceticum differed from A. woodii in that H2 was only evolved in the stationary phase, that the inhibition by H2 was observed at pH 8.5 but not at pH 7.5, anf that in the presence of fructose and H2+CO2 only fructose was utilized.The hydrogenase activity of fructose-grown cells of C. aceticum amounted to only 12% of that of H2+CO2-grown cells. With A. woodii a corresponding decrease of the activity of this enzyme was not observed. 相似文献
10.
Cytochrome oxidase has been resolved in acetic acid and high salt/detergent media. In 0.5% acetic acid, the smaller subunits of the enzyme are selectively extracted with retention of an insoluble protein fraction containing subunits I–IV, VII. This fraction retains all the heme and copper of the original enzyme in a spectrally unaltered state, and possesses enzymic activity comparable to the unresolved enzyme. The further removal of subunit IV from this fraction results in migration of heme and copper and modification of their spectral characteristics. Resolution of the enzyme in a high salt/detergent medium extracts smaller subunits (V–VII) together with subunit IV and some heme and copper. The heme associated with this enzymically active extract has spectral characteristics that are partially suggestive of hemea
3. It is suggested that the fraction of subunits I–IV, VII, resolved in dilute acetic acid, may represent the limit of resolution of the cytochrome oxidase complex that remains actively and spectrally indistinguishable from the original enzyme. 相似文献
11.
Hydrogenase was solubilized from the membrane of acetate-grown Methanosarcina barkeri MS and purification was carried out under aerobic conditions. The enzyme was reactivated under reducing conditions in the presence of H2. The enzyme showed a maximal activity of 120±40 mol H2 oxidized · min–1 · min–1 with methyl viologen as an electron acceptor, a maximal hydrogen production rate of 45±4 mol H2 · min–1 · mg–1 with methyl viologen as electron donor, and an apparent K
m for hydrogen oxidation of 5.6±1.7 M. The molecular weight estimated by gel filtration was 98,000. SDS-PAGE showed the enzyme to consist of two polypeptides of 57,000 and 35,000 present in a 1:1 ratio. The native protein contained 8±2 mol Fe, 8±2 mol S2–, and 0.5 mol Ni/mol enzyme. Cytochrome b was reduced by hydrogen in a solubilized membrane preparation. The hydrogenase did not couple with autologous F420 or ferredoxin, nor with FAD, FMN, or NAD(P)+. The physiological function of the membrane-bound hydrogenase in hydrogen consumption is discussed.Abbreviation CoM-S-S-HTP
the heterodisulfide of 7-mercaptoheptanoylthrconine phosphate and coenzyme M (mercaptoethanesulfonic acid) 相似文献
12.
Methanogenium organophilum, a non-autotrophic methanogen able to use primary and secondary alcohols as hydrogen donors, was grown on ethanol. Per mol of methane formed, 2 mol of ethanol were oxidized to acetate. In crude extract, an NADP+-dependent alcohol dehydrogenase (ADH) with a pH optimum of about 10.0 catalyzed a rapid (5 mol/min·mg protein; 22°C) oxidation of ethanol to acetaldehyde; after prolonged incubation also acetate was detectable. With NAD+ only 2% of the activity was observed. F420 was not reduced. The crude extract also contained F420: NADP+ oxidoreductase (0.45 mol/min·mg protein) that was not active at the pH optimum of ADH. With added acetaldehyde no net reduction of various electron acceptors was measured. However, the acetaldehyde was dismutated to ethanol and acetate by the crude extract. The dismutation was stimulated by NADP+. These findings suggested that not only the dehydrogenation of alcohol but also of aldehyde to acid was coupled to NADP+ reduction. If the reaction was started with acetaldehyde, formed NADPH probably reduced excess aldehyde immediately to ethanol and in this way gave rise to the observed dismutation. Acetate thiokinase activity (0.11 mol/min·mg) but no acetate kinase or phosphotransacetylase activity was observed. It is concluded that during growth on ethanol further oxidation of acetaldehyde does not occur via acetylCoA and acetyl phosphate and hence is not associated with substrate level phosphorylation. The possibility exists that oxidation of both ethanol and acetaldehyde is catalyzed by ADH. Isolation of a Methanobacterium-like strain with ethanol showed that the ability to use primary alcohols also occurs in genera other than Methanogenium.Non-standard abbreviations ADH
alcohol dehydrogenase
- Ap5ALi3
P1,P5-Di(adenosine-5-)pentaphosphate
- DTE
dithioerythritol (2,3-dihydroxy-1,4-dithiolbutane)
- F420
N-(N-l-lactyl--l-glutamyl)-l-glutamic acid phosphodiester of 7,8-dimethyl-8-hydroxy-5-deazariboflavin-5-phosphate
-
Mg.
Methanogenium
- OD578
optical density at 578 nm
- PIPES
1,4-piperazine-diethanesulfonic acid
- TRICINE
N-(2-hydroxy-1,1-bis[hydroxymethyl]methyl)-glycine
- Tris
2-amino-2-hydroxy-methylpropane-1,3-diol
- U
unit (mol substrate/min) 相似文献
13.
14.
Methanogenesis by a Syntrophomonas wolfei/ Methanospirillum hungatei coculture was inhibited in presence of ethylene and the hydrogenation catalyst Pd-BaSO4. However, butyrate oxidation by S. wolfei continued and ethylene was reduced to ethane. Per mol of butyrate oxidized, 2.4 mol acetate was produced and 0.8 mol ethylene was reduced. Acetylene, propylene and butene were less effective as H2 acceptors than ethylene, and addition of bromoethanesulfonic acid was necessary to inhibit methanogenesis in the presence of the two longer-chain olefins. Other hydrogenation catalysts were less effective in the order Pd-charcoal < PE-asbestos < Pd-PEI beads < Pt-Al2O3, Pd-CaCO3. Optimal ethylene hydrogenation was achieved with still incubation in presence of 7.2 mg Pd-BaSO4 and 0.7 g sand per ml medium. The higher catabolic rate of S. wolfei in presence of the methanogen indicated that the biological H2 removal mechanism was more efficient than the catalytic olefin reduction.Abbreviations BES
bromoethane sulfonic acid
- VFA
volatile fatty acid 相似文献
15.
Harvesting of Chlorella vulgaris using a bioflocculant from Paenibacillus sp. AM49 总被引:12,自引:0,他引:12
Hee-Mock Oh Seog June Lee Myung-Hwan Park Hee-Sik Kim Hyoung-Chin Kim Jung-Hoon Yoon Gi-Seok Kwon Byung-Dae Yoon 《Biotechnology letters》2001,23(15):1229-1234
Microbial flocculants for harvesting mass cultured Chlorella vulgaris were screened and that from Paenibacillussp. AM49 was identified as the best. The flocculation efficiency of this bioflocculant increased with the pH within a range of pH 5–11 and was 83%, which was higher than the 72% and 78% produced by aluminum sulfate and polyacrylamide, respectively. The highest flocculation efficiency was with 6.8 mm CaCl2 as co-flocculant. The bioflocculant from Paenibacillussp. AM49 can be used effectively to harvest C. vulgaris from large-scale cultures. 相似文献
16.
Methanobacterium thermoautotrophicum, growing on medium supplemented with 2 mol 63NiCl2/l, was found to take up 1.2 mol 63Ni per g cells (dry weight). More than 70% of the radioisotope was incorporated into a compound, which dissociated from the protein fraction after heat treatment, was soluble in 70% acetone, and could be purified by chromatography on QAE-Sephadex A-25, Sephadex G-25, and DEAE cellulose. The purified 63Ni labelled compound had an absorption spectrum and properties identical to those of factor F
430 and is therefore considered to be identical with factor F
430.Factor F
430, a compound of molecular weight higher than 1000 with an absorbance maximum at 430 nm, has recently been purified from Methanobacterium thermoautotrophicum (Gunsalus and Wolfe, 1978). The structure and function of this compound are not yet known. 相似文献
17.
In C4 grasses belonging to the NADP-malic enzyme-type subgroup, malate is considered to be the predominant C4 acid metabolized during C4 photosynthesis, and the bundle sheath cell chloroplasts contain very little photosystem-II (PSII) activity. The present studies showed that Flaveria bidentis (L.), an NADP-malic enzyme-type C4 dicotyledon, had substantial PSII activity in bundle sheath cells and that malate and aspartate apparently contributed about equally to the transfer of CO2 to bundle sheath cells. Preparations of bundle sheath cells and chloroplasts isolated from these cells evolved O2 at rates between 1.5 and 2 mol · min–1 · mg–1 chlorophyll (Chl) in the light in response to adding either 3-phosphoglycerate plus HCO
3
–
or aspartate plus 2-oxoglutarate. Rates of more than 2 mol O2 · min–1 · mg–1 Chl were recorded for cells provided with both sets of these substrates. With bundle sheath cell preparations the maximum rates of light-dependent CO2 fixation and malate decarboxylation to pyruvate recorded were about 1.7 mol · min–1 · mg–1 Chl. Compared with NADP-malic enzyme-type grass species, F. bidentis bundle sheath cells contained much higher activities of NADP-malate dehydrogenase and of aspartate and alanine aminotransferases. Time-course and pulse-chase studies following the kinetics of radiolabelling of the C-4 carboxyl of C4 acids from 14CO2 indicated that the photosynthetically active pool of malate was about twice the size of the aspartate pool. However, there was strong evidence for a rapid flux of carbon through both these pools. Possible routes of aspartate metabolism and the relationship between this metabolism and PSII activity in bundle sheath cells are considered.Abbreviations DHAP
dihydroxyacetone phosphate
- NADP-ME(-type)
NADP-malic enzyme (type)
- NADP-MDH
NADP-malate dehydrogenase
- OAA
oxaloacetic acid
- 2-OG
2-oxoglutarate
- PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- Pi
orthophosphate
- Ru5P
ribulose 5-phosphate 相似文献
18.
The activities of several enzymes, including ribulose-1,5-diphosphate (RuDP) carboxylase (EC 4.1.1.39) and phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured as a function of leaf age in Z. mays. Mature leaf tissue had a RuDP-carboxylase activity of 296.7 mol CO2 g-1 fresh weight h-1 and a PEP-carboxylase activity of 660.6 mol CO2 g-1 fresh weight h-1. In young corn leaves the activity of the two enzymes was 11 and 29%, respectively, of the mature leaves. In senescent leaf tissue, RuDP carboxylase activity declined more rapidly than that of any of the other enzymes assayed. On a relative basis the activities of NADP malic enzyme (EC 1.1.1.40), aspartate (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2), and NAD malate dehydrogenase (EC 1.1.1.37) exceeded those of both PEP and RuDP carboxylase in young and senescent leaf tissue. Pulse-chase labeling experiments with mature and senescent leaf tissue show that the predominant C4 acid differs between the two leaf ages. Labeling of alanine in senescent tissue never exceeded 4% of the total 14C remaining during the chase period, while in mature leaf tissue alanine accounted for 20% of the total after 60 s in 12CO2. The activity of RuDP carboxylase during leaf ontogeny in Z. mays parallels the development of the activity of this enzyme in C3 plants.Abbreviations RuDP
ribulose-1,5-diphosphate
- PEP
phosphoenol pyruvate
- PGA
3-phosphoglycerate 相似文献
19.
6-Phosphogluconate dehydrogenase (6PG) was purified from rat small intestine with 36% yield and a specific activity of 15 U/mg.
On SDS/PAGE, one band with a mass of 52 kDa was found. On native PAGE three protein and two activity bands were observed.
The pH optimum was 7.35. Using Arrhenius plots, Ea, ΔH, Q10 and Tm for 6PGD were found to be 7.52 kcal/mol, 6.90 kcal/mol, 1.49 and 49.4°C, respectively. The enzyme obeyed “Rapid Equilibrium
Random Bi Bi” kinetic model with Km values of 595 ± 213 μM for 6PG and 53.03±1.99 μM for NADP. 1/Vm versus 1/6PG and 1/NADP plots gave a Vm value of 8.91±1.92 U/mg protein. NADPH is the competitive inhibitor with a Ki of 31.91±1.31 μM. The relatively small Ki for the 6PGD:NADPH complex indicates the importance of NADPH in the regulation of the pentose phosphate pathway through G6PD
and 6PGD. 相似文献
20.
Although the activation of phospholipase A2 (PLA2) in ras-transformed cells has been well documented, the mechanisms underlying this activation are poorly understood. In this study we tried to elucidate whether the membrane phospholipid composition and physical state influence the activity of membrane-associated PLA2 in ras-transformed fibroblasts. For this purpose membranes from non-transfected and ras-transfected NIH 3T3 fibroblasts were enriched with different phospholipids by the aid of partially purified lipid transfer protein. The results showed that of all tested phospholipids only phosphatidylcholine (PC) increased PLA2 activity in the control cells, whereas in their transformed counterparts both PC and phosphatidic acid (PA) induced such effect. Further we investigated whether the activatory effect was due only to the polar head of these phospholipids, or if it was also related to their acyl chain composition. The results demonstrated that the arachidonic acid-containing PC and PA molecules induced a more pronounced increase of membrane-associated PLA2 activity in ras-transformed cells compared to the corresponding palmitatestearate- or oleate- containing molecular species. However, we did not observe any specific effect of the phospholipid fatty acid composition in non-transformed NIH 3T3 fibroblasts. In ras-transformed cells incubated with increasing concentrations of arachidonic acid, PLA2 activity was altered in parallel with the changes of the cellular content of this fatty acid. The role of phosphatidic and arachidonic acids as specific activators of PLA2 in ras-transformed cells is discussed with respect to their possible role in the signal transduction pathways as well as in the processes of malignant transformation of cells. 相似文献