Linolenic acid binding by chloroplasts

The binding of linolenic acid with chloroplasts was investigatedwith ¹⁴C-labelled linolenic acid. The effect of the fatty acidon the activity of the electron transport system was also studied. The amount of linolenic acid bound to chloroplasts increasedwith increasing concentration of the fatty acid added in a mannersuggesting a cooperative mode of binding. At the highest concentrationof linolenic acid added (100 µM), the molar ratio of boundfatty acid to chlorophyll was four. The bound fatty acid to chlorophyll ratios were inversely proportionalto the amounts of chloroplasts added. The bound fatty acid wasreleased by addition of bovine serum albumin or by washing ofthe chloroplasts. The mode of release during repeated washingindicates that binding of linolenic acid to chloroplast membraneoccurred through partition of the fatty acid between the membraneand the aqueous medium. Time courses and temperature dependency of the development oflinolenic acid-induced inhibition of the Hill reaction weremarkedly different from those of the fatty acid binding. Theinhibition was at least partially reversible. The results indicatethat inactivation of electron transport is due to disorganizationof the functional integrity of the membrane caused by penetrationof the fatty acid molecules into the hydrophobic region of membrane. ¹ Present address: Biological Laboratory, Nippon Medical School,Kosugi, Kawasaki, Japan. (Received December 16, 1976; )     

Salivary uric acid at the acidic pH of the stomach is the principal defense against nitrite-derived reactive species: sparing effects of chlorogenic acid and serum albumin

A complex antioxidant system is present in human saliva, with uric acid being the most concentrated component. Ascorbic acid, present at low concentrations in saliva, is actively secreted into the gastric lumen. We report that ascorbic acid added to human saliva at pH 2 was consumed within a few minutes, regenerating HNO₂, whereas uric acid was consumed relatively slowly in a nitrite-dependent manner. The consumption of uric acid was (i) rapid under normoxic conditions and slower at low oxygen tensions, (ii) coupled to NO release, (iii) linked to the decrease in nitrite consumption and in nitrate formation, and (iv) unaffected by the nitrosation catalyst thiocyanate. Both chlorogenic acid and bovine serum albumin, representative of a phenol- and a protein-rich meal, respectively, were able to spare uric acid, although chlorogenic acid increased, whereas bovine serum albumin inhibited, NO release. We hypothesize that the major role of uric acid in saliva at pH 2 could be to preserve the stomach from the formation of toxic nitrogen species and that low levels of uric acid, together with ascorbic acid consumption, may contribute to the high occurrence of tumors at the gastroesophageal junction and cardia. The sparing effects of dietary compounds may therefore be an important not fully appreciated effect.     

Manipulation of fatty acid composition of membrane phospholipid and its effects on cell growth in mouse LM cells

Fatty acid composition of the phospholipids of mouse LM cells grown in suspension culture in serum-free chemically defined medium was modified by supplementing the medium with various fatty acids bound to bovine serum albumin.Following supplementation with saturated fatty acids of longer than 15 carbons (100 μM) profound inhibition of cell growth occurred; this inhibitory effect was completely abolished when unsaturated fatty acids were added at the same concentration. Supplementing with unsaturated fatty acids such as linoleic acid, linolenic acid or arachidonic acid had no effect on the cell growth.Fatty acid composition of membrane phospholipids could be manipulated by addition of different fatty acids. The normal percentage of unsaturated fatty acids in LM cell membrane phospholipids (63%) was reduced to 35–41% following incorporation of saturated fatty acids longer than 15 carbon atoms and increased to 72–82% after addition of unsaturated fatty acids.A good correlation was found between the unsaturated fatty acid content of membrane phospholipids and cell growth. When incorporated saturated fatty acids reduced the percentage of unsaturated fatty acids in membrane phospholipids to less than 50%, severe inhibition of the cell growth was found. Simultaneous addition of an unsaturated fatty acid completely abolished this effect of saturated fatty acids.     

Interaction of linolenic acid with bound quinone molecules in Photosystem II. Time-resolved optical and electron spin resonance studies

Time-resolved spectroscopic techniques, including optical flash photolysis and electron spin resonance spectroscopy, have been utilized to monitor electron-transport activity in Photosystem II subchloroplast particles. These studies have indicated that in the presence of 100 microM linolenic acid (1) a high initial fluorescence yield (Fi) is observed upon steady-state illumination of the dark-adapted sample; (2) flash-induced absorption transients (t greater than 10 mus) in the region of 820 nm, attributed to P-680+, are first slowed, then abolished; and (3) electron spin resonance Signal IIs and Signal IIf (Z+) are not detectable. Upon reversal of linolenic acid inhibition by washing with bovine serum albumin, optical and electron spin resonance transients originating from the photooxidation of P-680 are restored. Similarly, the variable component of fluorescence is recovered with an accompanying restoration of Signal IIs and Signal IIf. The data indicate that linolenic acid affects two inhibition sites in Photosystem II: one located between pheophytin and QA on the reducing side, and the other between electron donor Z and P-680 on the oxidizing side. Since both sites are associated with bound quinone molecules, we suggest that linolenic acid interacts at the level of quinone binding proteins in Photosystem II.     

Involvement of acyl exchange between acyl-CoA and phosphatidylcholine in the remodelling of phosphatidylcholine in microsomal preparations of rat lung

Microsomal membrane preparations from rat lung catalyse the incorporation of radioactive linolenic acid from [14C]linolenoyl-CoA into position 2 of sn-phosphatidylcholine. The incorporation was stimulated by bovine serum albumin and free CoA. Free fatty acids in the incubation mixtures were not utilised in the incorporation into complex lipids. Fatty acids were transferred to the acyl-CoA pool during the incorporation of linolenic acid into phosphatidylcholine. An increase in lysophosphatidylcholine occurred in incubations containing both bovine serum albumin and free CoA and in the absence of acyl-CoA. The results were consistent with an acyl-CoA: lysophosphatidylcholine acyltransferase operating in both a forwards and backwards direction and thus catalysing the acyl exchange between acyl-CoA and position 2 of sn-phosphatidylcholine. In incubations with mixed species of acyl-CoAs, palmitic acid was the major fatty acid substrate transferred to phosphatidylcholine in acyl exchange, whereas this acid was completely selected against in the acylation of added lysophosphatidylcholine. The selectivity for palmitoyl-CoA was particularly enhanced when the mixed acyl-CoA substrate was presented to the microsomes in molar concentrations equivalent to the molar ratios of the fatty acids in position 2 of sn-phosphatidylcholine. During acyl exchange, the predominant fatty acid transferred to phosphatidylcholine from acyl-CoA was palmitic acid, whereas arachidonic acid was particularly selected for in the reverse reaction from phosphatidylcholine to acyl-CoA. A hypothesis is presented to explain the differential selectivity for acyl species between the forward and backward reactions of the acyltransferase that is based upon different affinities of the enzyme for substrates at high and low concentrations of acyl donor. Acyl exchange between acyl-CoA and phosphatidylcholine offers, therefore, a possible mechanism for the acyl-remodelling of phosphatidylcholine for the production of lung surfactant.     

Multiple effects of linolenic acid addition to pea thylakoids

The addition of linolenic acid to thylakoids produces various pH-dependent effects. We have demonstrated a binding site near the Photosystem (PS) II center with a pK_a of 6.5: when linolenic acid is unprotonated it induces in the dark a rise of the initial fluorescence level, the latter being similar to the maximum fluorescence obtained during illumination of untreated thylakoids. The comparison of the fluorescence lifetimes in the presence and absence of linolenic acid leads us to conclude that the charge stabilisation on the primary acceptor, Q, is prevented by linolenic acid. A second binding site on the protein carrying B, the secondary acceptor of PS II, has also been demonstrated for linolenic acid. It has a 3-(3,4-dichlorophenyl)-1,1-dimethylurea-type effect both in the protonated and unprotonated forms. Finally, measurements of electrophoretic mobility of the thylakoids indicate several other sites of linolenic acid inclusion with an average pK_a of 5.7. At alkaline pH the presence of unprotonated linolenic acid increases the charge density on the membrane. As a result a higher concentration of divalent cations is needed to obtain fluorescence and stacking changes than for untreated thylakoids. The presence, at acidic pH values, of the unprotonated form of linolenic acid leads to the inhibition of cation-induced fluorescence changes, probably by preventing the movement of chlorophyll-protein complexes in the membrane.     

Lowry protein determination on membrane preparations: need for standardization by amino acid analysis

The protein content of three membrane protein preparations has been determined by the Lowry method with bovine serum albumin as a standard and also by quantitative amino acid analysis as an absolute method. The results differ considerably, the Lowry method giving 29–42% higher values. This implies that many published data for such proteins, based on Lowry protein determinations with bovine serum albumin as the generally applied standard, are in error. Suggestions are made on how to standardize the Lowry method so that reliable values can be obtained for membrane protein.     

Investigation of Ternary Complex Formations of Polyacrylic Acid with Bovine Serum Albumin in the Presence of Metal Ions by Fluorescence and Dynamic Light Scattering Measurements

In this paper, the complex formation of bovine serum albumin (BSA) and polyacrylic acid (PAA) in the presence metal ions at pH = 7 has been examined by using fluorescence and dynamic light scattering measurements. It has been observed that the most stable complexes of polyacrylic acid and bovine serum albumin have occurred in the presence of copper(II) ions. The other ions have the ability to form weak complexes between polyions and bovine serum albumin. To prior characterizing the interaction between bovine serum albumin and polyacrylic acid, the dynamic light scattering technique have been applied to determine the intensity-size distributions of the solutions of bovine serum albumin, polyacrylic acid, and ternary mixtures containing various molar ratios of bovine serum albumin to polyacrylic acid (the molar ratios of bovine serum albumin to polyacrylic acid has been taken equal to 0.5, 1.0, 1.5, 2.0 and 2.5) prepared at different molar ratios of copper(II) ions/acrylic acid unit. When the molar ratio of copper(II) ions to acrylic acid in the ternary mixtures has been lower than and equals to 0.3, two peaks have been observed in the curves of the intensity-size distributions due to contents of free bovine serum albumin and ternary complexes of polyacrylic acid-copper(II)-bovine serum albumin whereas when the molar ratio of copper(II) ions to acrylic acid equals to 0.4, the hydrodynamic diameter has pointed out only one peak. This result indicates that soluble and stable ternary complexes has occurred when the molar ratio of copper(II) ions to acrylic acid has been taken equal to 0.4.     

Fusion of lamellar body with plasma membrane is driven by the dual action of annexin II tetramer and arachidonic acid

Annexin II has been implicated in membrane fusion during the exocytosis of lamellar bodies from alveolar epithelial type II cells. Most previous studies were based on the fusion assays by using model membranes. In the present study, we investigated annexin II-mediated membrane fusion by using isolated lamellar bodies and plasma membrane as determined by the relief of octadecyl rhodamine B (R18) self-quenching. Immunodepletion of annexin II from type II cell cytosol reduced its fusion activity. Purified annexin II tetramer (AIIt) induced the fusion of lamellar bodies with the plasma membrane in a dose-dependent manner. This fusion is Ca2+-dependent and is highly specific to AIIt because other annexins (I and II monomer, III, IV, V, and VI) were unable to induce the fusion. Modification of the different functional residues of AIIt by N-ethylmaleimide, nitric oxide, or peroxynitrite abolished AIIt-mediated fusion. Arachidonic acid enhanced AIIt-mediated fusion and reduced its Ca2+ requirement to an intracellularly achievable level. This effect is due to membrane-bound arachidonic acid, not free arachidonic acid. Other fatty acids including linolenic acid, palmitoleic acid, myristoleic acid, stearic acid, palmitic acid, and myristic acid had little effect. AIIt-mediated fusion was suppressed by the removal of arachidonic acid from lamellar body and plasma membrane using bovine serum albumin. The addition of arachidonic acid back to the arachidonic acid-depleted membranes restored its fusion activity. Our results suggest that the fusion between lamellar bodies with the plasma membrane is driven by the synergistic action of AIIt and arachidonic acid.     

Bovine serum albumin decreases 4-methyl-2-oxovalerate utilization by isolated rat hepatocytes.

Binding of 4-methyl-2-oxo[1-14C]valerate to defatted bovine serum albumin inhibited the utilization of this 2-oxo acid by fed-rat hepatocytes in vitro. With 0-50g of albumin/l in the presence of 0.05mM 2-oxo acid or on increasing the 2-oxo acid concentration from 0 to 2mM in the presence of 26g of albumin/l, the extent of inhibition was essentially dependent on the change in the free 2-oxo acid concentration. Intrahepatocyte 4-methyl-2-oxo[1-14C]valerate concentrations were similar to extracellular free 2-oxo acid concentrations, suggesting equilibration so that the plasma membrane appears not to be rate-limiting for the utilization of this substrate by the isolated liver cells.     

Activation of purified soluble guanylate cyclase by arachidonic acid requires absence of enzyme-bound heme

The mechanism by which arachidonic acid activates soluble guanylate cyclase purified from bovine lung is partially elucidated. Unlike enzyme activation by nitric oxide (NO), which required the presence of enzyme-bound heme, enzyme activation by arachidonic acid was inhibited by heme. Human but not bovine serum albumin in the presence of NaF abolished activation of heme-containing guanylate cyclase by NO and nitroso compounds, whereas enzyme activation by arachidonic acid was markedly enhanced. Addition of heme to enzyme reaction mixtures restored enzyme activation by NO but inhibited enzyme activation by arachidonic acid. Whereas heme-containing guanylate cyclase was activated only 4- to 5-fold by arachidonic or linoleic acid, both heme-deficient and albumin-treated heme-containing enzymes were activated over 20-fold. Spectrophotometric analysis showed that human serum albumin promoted the reversible dissociation of heme from guanylate cyclase. Arachidonic acid appeared to bind to the hydrophobic heme-binding site on guanylate cyclase but the mechanism of enzyme activation was dissimilar to that for NO or protoporphyrin IX. Enzyme activation by arachidonic acid was insensitive to Methylene blue or KCN, was inhibited competitively by metalloporphyrins, and was abolished by lipoxygenase. Whereas NO and protoporphyrin IX lowered the apparent Km and Ki for MgGTP and uncomplexed Mg2+, arachidonic and linoleic acids failed to alter these kinetic parameters. Thus, human serum albumin can promote the reversible dissociation of heme from soluble guanylate cyclase and thereby abolish enzyme activation by NO but markedly enhance activation by polyunsaturated fatty acids. Arachidonic acid activates soluble guanylate cyclase by heme-independent mechanisms that are dissimilar to the mechanism of enzyme activation caused by protoporphyrin IX.     

Eicosapentaenoic acid and prostacyclin production by cultured human endothelial cells

Human umbilical vein endothelial cells incorporate eicosapentaenoic acid (EPA) when this fatty acid is present in the culture medium. From 30 to 70% of the uptake remains as EPA, and much of the remainder is elongated to docosapentaenoic acid. All of the cellular glycerophospholipids become enriched with EPA and docosapentaenoic acid, with the largest increase in EPA occurring in the choline glycerophospholipids. When this fraction is enriched with EPA, it exhibits a large decrease in arachidonic acid content. Cultures exposed to tracer amounts of [1-14C]linolenic acid in 5% fetal bovine serum convert as much as 17% of the radioactivity to EPA. The conversion is reduced, however, in the presence of either 20% fetal bovine serum or 50 microM linolenic acid. Like arachidonic acid, some newly incorporated EPA was released from the endothelial cells when the cultures were exposed to thrombin. However, as compared with arachidonic acid, only very small amounts of EPA were converted to prostaglandins. Cultures enriched with EPA exhibited a 50 to 90% reduction in capacity to release prostacyclin (PGI2) when subsequently stimulated with thrombin, calcium ionophore A23187, or arachidonic acid. The degree of inhibition was dependent on the time of exposure to EPA and the EPA concentration, and it was not prevented by adding a reversible cyclooxygenase inhibitor, ibuprofen, during EPA supplementation. EPA appears to decrease the capacity of the endothelial cells to produce PGI2 in two ways: by reducing the arachidonic acid content of the cell phospholipid precursor pools and by acting as an inhibitor of prostaglandin production. These findings suggest that regimens designed to reduce platelet aggregation and thrombosis by EPA enrichment may also reduce the capacity of the endothelium to produce PGI2.     

RESPIRATION AND PROTEIN SYNTHESIS IN ESCHERICHIA COLI MEMBRANE-ENVELOPE FRAGMENTS : II. Effects of Fatty Acids and Albumin on Respiration

Fatty acids inhibited the ability of Escherichia coli membrane-envelope fragments to catalyze the oxidation of succinate and nicotinamide adenine dinucleotide, reduced form (NADH) and also inhibited the response of the Clark oxygen electrode to nonenzymatic oxygen uptake. In all cases, unsaturated fatty acids were much more inhibitory than saturated fatty acids. Albumin afforded complete protection from inhibition in the nonenzymatic oxygen-uptake experiments but only partial protection for the respiratory activities of the membrane fragments. The succinoxidase activity was totally inhibited by bovine serum albumin at concentrations that inhibited succinate dehydrogenase only slightly and NADH oxidase not at all. The E. coli acellular preparation showed no dehydrogenase or oxidase activity for any of the fatty acids under a variety of conditions. These conditions included variations of pH, concentration of fatty acids, and the presence or absence of albumin, CoA, ATP, NAD, cysteine, succinate, and carnitine. It thus appears that E. coli grown in the absence of fatty acid can not use fatty acids as an energy source.     

Binding of 13-HODE and 15-HETE to phospholipid bilayers, albumin, and intracellular fatty acid binding proteins. implications for transmembrane and intracellular transport and for protection from lipid peroxidation

Transport and utilization of fatty acids (FA) in cells is a multistep process that includes adsorption to and movement across the plasma membrane and binding to intracellular fatty acid binding proteins (FABP) in the cytosol. We monitored the transbilayer movement of several polyunsaturated FA and oxidation products (13-hydroxy octadecadienoic acid (HODE) and 15-hydroxytetraenoic acid (HETE)) in unilamellar protein-free phospholipid vesicles containing a fluorescent pH probe. All FA diffused rapidly by the flip-flop mechanism across the model membrane, as revealed by pH changes inside the vesicle. This result suggests that FA oxidation products generated in the cell could cross the plasma or nuclear membrane spontaneously without a membrane transporter. To illuminate features of extra- and intracellular transport, the partitioning of unsaturated FA and oxidized FA between phospholipid vesicles and albumin or FABP was studied by the pyranin assay. These experiments showed that all polyunsaturated FA and oxidized FA (13-HODE and 15-HETE) desorbed rapidly from the phospholipid bilayer to bind to bovine serum albumin, which showed a slight preference for the unsaturated FA over the oxidized FA. FABP rapidly bound FA in the presence of phospholipid bilayers, with a preference of 13-HODE over the unsaturated FA and with a specificity depending on the type of FABP. Liver FABP was significantly more effective than intestinal FABP in binding 13-HODE in the presence of vesicles. The more effective binding of the FA metabolite, 13-HODE, than its precursor 18:2 by FABP may help protect cellular membranes from potential damage by monohydroxy fatty acids and may contribute a pathway for entry of 13-HODE into the nucleus.     

Cellular energy metabolism during fetal development. II. Fatty acid oxidation by the developing heart

In view of the importance of fatty acids as substrates for the mature heart, fatty acid oxidation by fetal and calf heart mitochondria has been investigated. Free fatty acids of 10 carbon units or less which exhibit carnitine-independent transport into mitochondria were effective substrates for oxidative phosphorylation in both fetal and calf heart mitochondria. Efficient oxidative phosphorylation with these substrates was dependent upon the presence of bovine serum albumin in the assay medium to reverse the uncoupling effects of the fatty acids. In the presence of bovine serum albumin, ADP/0 ratios were in the range of 3 when short-chain fatty acids and carnitine esters of short- and long-chain fatty acids were substrates. Compared with calf heart mitochondria, fetal heart mitochondria showed decreased carnitine-dependent oxidation of palmityl-CoA. However, the oxidation of palmitylcarnitine was identical in both. These data suggest that the formation of palmitylcarnitine is rate limiting for palmityl-CoA oxidation by the fetal heart mitochondria and that long-chain fatty acids are not readily oxidized by the fetal heart.     

Binding to specific receptors on oocyte plasma membranes by serum phosvitin-lipovitellin

Specific binding sites for the serum complex of phosvitin and lipovitellin have been shown to exist on the outer surface of rapidly growing chicken oocytes. The existence and specificity of these sites were demonstrated by competition for binding to unfixed oocyte membrane fragments and by displacement of already bound and labeled phosvitin-lipovitellin from formaldehyde-fixed membranes. Only unlabeled phosvitin-lipovitellin competed with the ¹²⁵I-labeled complex for binding to the fragments or displacement of bound label; IgG isolated from egg yolks and bovine serum albumin were ineffective.     

Formation of cholic acid from 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid by rat liver peroxisomes

In a previous study, it was shown that the peroxisomal fraction of rat liver, isolated by Percoll gradient centrifugation of a light mitochondrial fraction, was able to catalyze conversion of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) into cholic acid (Pedersen, J. I., and J. Gustafsson, 1980. FEBS Lett. 121: 345-348). In the present work, this peroxisomal THCA-oxidizing system has been studied in more detail. The peroxisomes were prepared by sucrose gradient centrifugation. By use of different marker enzymes, it was confirmed that the major part of the activity in the light mitochondrial fraction was located in the peroxisomes. The reaction was absolutely dependent on the presence of Mg2+, CoA, ATP, and NAD+ in the reaction medium. In addition to cholic acid, small amounts of 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid were detected as product. Provided the peroxisomes were preincubated with ATP and CoA, the reaction was linear with time up to 75 min. It was linear with peroxisomal protein and the pH optimum was 8. The reaction was stimulated by FAD (ca. 50%), by cytosolic protein (about twofold), by microsomal protein (about twofold), bovine serum albumin (about sevenfold), and by KCN (75% at 1 mM). In the absence of bovine serum albumin in the medium the K'm for the overall reaction was 1.4 X 10(-6) M and the maximum rate was 4.3 nmol X mg-1 X hr-1. In the presence of bovine serum albumin, the K'm increased to 6.3 X 10(-6) M and the maximum rate to about 32 nmol X mg-1 X hr-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum Albumin Washing Specifically Enhances Arachidonate Incorporation into Synaptosomal Phosphatidylinositols

Arachidonate incorporation into synaptosomal phospholipids was shown to be affected by factors including the procedure for preparation of the membrane fractions and preincubation of synaptosomes prior to assay of incorporation of arachidonate into both phosphatidylcholine (PC) and phosphatidylinositol (PI). However, the inhibition toward incorporation into PIs, but not PCs, was fully reversed when the membranes were washed with bovine serum albumin. A twofold increase in arachidonate incorporation into PIs was also observed when freshly prepared synaptosomes were washed with serum albumin immediately before assay of incorporation activity. The inhibitory action is thought to be due to an increase in polyunsaturated fatty acids and/or their oxidation products which may then elicit a special effect on the acyltransferase responsible for transferring arachidonate into phosphatidylinositols. The differences in fatty acid uptake and response to serum albumin also suggest the presence of different acyltransferase for acyl transfer to PIs and PCs.     

The time-course development of the effects of ethanol ingestion on choline oxidase

Male rats were fed a low-fat diet containing 36% of calories as ethanol, and the time-course development of the effects of ethanol on liver mitochondrial oxidation of choline was determined. Ethanol induced an increase in choline oxidase at days 2, 5 and 7 after being introduced into the diet. Due to an observed 32% increase in total fatty acids in the whole liver, defatted bovine serum albumin was added to the buffer used to homogenize the liver. The presence of bovine serum albumim resulted in a significant decrease in choline oxidase activity at days 2 and 5; however, ethanol still induced an increase in choline oxidase activity in these mitochondria. The total fatty acid concentration of mitochondria prepared in the absence of bovine serum albumin increased steadily until day 5; however, by day 7 the fatty acid concentration had returned to control levels. The addition of bovine serum albumin to the homogenization medium prevented the increase in the total amount of fatty acids. The fatty acid composition of the bovine serum albumin-treated mitochondria, however, was not different from the mitochondria is isolated in the absence of bovine serum albumin. Further, the addition of a free fatty acid to isolated mitochondrial preparations caused about a 100% increase in choline oxidase. These data are consistent with the idea that choline oxidase may be regulated to some extent by an influx or an increase in free fatty acids in the liver as a result of ethanol ingestion. Thus, a second mechanism has been described which contributes to the increase in choline oxidase after ethanol ingestion.     

Interaction of rat liver microsomes containing saturated or unsaturated fatty acids with fatty acid binding protein: Peroxidation effect

In the studies described here rat liver microsomes containing labeled palmitic, stearic, oleic or linoleic acids were incubated with fatty acid binding protein (FABP) and the rate of removal of¹⁴C-labeled fatty acids from the membrane by the soluble protein was measured using a model system. More unsaturated than saturated fatty acids were removed from native liver microsomes incubated with similar amounts of FABP. Thein vitro peroxidation of microsomal membranes mediated by ascorbate-Fe⁺⁺, modified its fatty acid composition with a considerable decrease of the peroxidizability index. These changes in the microsomes facilitated the removal of oleic and linoeic acids by FABP, but the removal of palmitic and stearic acids was not modified. This effect is proposed to result from a perturbation of membrane structure following peroxidation with release of free fatty acids from susceptible domains.Abbreviations BSA bovine serum albumin - FABP fatty acid binding protein