Radioactive Fatty Acids Research Articles

Synthesis of milk fat from beta-hydroxybutyrate and acetate in lactating goats.

SummaryThe relative importance of β-hydroxybutyric acid (BHBA) and acetate as precursors for milk-fat synthesis was studied in lactating goats by infusing separately tracer quantities of [3−14C]DL-BHBA and [1−14C]acetate into the jugular vein, and [1−14C]butyrate into the portal vein. The concentrations and specific radioactivities of blood plasma constituents, the yields and specific radioactivities of individual milk fatty acids and the relative radioactivities of individual carbon atoms of milk fatty acids were determined.The infusion of [1−14C]butyrate resulted in the appearance of labelled BHBA in the blood plasma which behaved almost identically with infused [14C]BHBA as a precursor for milk fatty acids.The relative radioactivity of carbon atoms of the fatty acids of milk fat following the infusions provided direct evidence that BHBA had provided an intact 4-carbon unit at the methyl end of each fatty-acid chain. Acetate provided 2-carbon units both for the elongation of the 4-carbon units and for completede novosynthesis. BHBA also provided 2-carbon units which behaved in a similar fashion to those from acetate.Acetate and BHBA together accounted for all of the C4–C12acids of milk fat, about 75% of the C14, 45% of the C16and 10% of the C18.The total contributions of the various precursors to the fatty acids of milk fat were: acetate 42%, BHBA 9·4% and other plasma precursors (by difference) 48·6%.

Renewal of fatty acids in the membranes of visual cell outer segments.

The renewal of fatty acids in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with tritiated palmitic, stearic, or arachidonic acids. Most of the radioactive material could be extracted from the retina with chloroform-methanol, indicating that the fatty acids had been esterified in lipids. Analysis of the extracts, after injection of [(3)H]palmitic acid, revealed that the radioactivity was predominantly in phospholipid. Palmitic acid was initially concentrated in the pigment epithelium, particularly in oil droplets which are storage sites for vitamin A esterified with fatty acid. The cytoplasm, but not the nucleus of these cells, was also heavily labeled. Radioactive fatty acid was bound immediately to the visual cell outer segment membranes, including detached rod membranes which had been phagocytized by the pigment epithelium. This is believed to be due to fatty acid exchange in phospholipid molecules already situated in the membranes. Gradually, the concentration of radioactive material in the visual cell outer segment membranes increased, apparently as a result of the addition of new phospholipid molecules, possibly augmented by the transfer from the pigment epithelium of esterified vitamin A. Injected fatty acid became particularly concentrated in new membranes which are continually assembled at the base of rod outer segments. This localized concentration was short-lived, apparently due to the rapid renewal of fatty acid. The results support the conclusion that rods renew the lipids of their outer segments by membrane replacement, whereas both rods and cones renew the membrane lipids by molecular replacement, including fatty acid exchange and replacement of phospholipid molecules in existing membranes.

Lipid Biosynthesis in Green Leaves of Developing Maize

Successive leaf sections from the base to the tip of rapidly developing leaves of 7-day-old maize (Zea mays var. Kelvedon Glory), grown in the light, utilized acetate for fatty acid biosynthesis in a very divergent manner. Basal regions of the leaf containing proplastids synthesized insignificant proportions of unsaturated fatty acids and appreciable proportions of fatty acids with 20 or more carbon atoms. An increase in the light intensity during incubations with acetate-1-(14)C resulted in very little enhancement of either total or polyunsaturated fatty acid biosynthesis in this tissue.When the distal leaf sections, containing mesophyll chloroplasts with well developed grana and bundle sheath chloroplasts without grana, were incubated with acetate at 150 ft-c and 30 C, approximately 30% of the newly synthesized fatty acids were unsaturated (mainly 18: 1 and 18: 2). At 2800 ft-c and 20 C, 60% of the fatty acids were unsaturated and the total synthesis of fatty acids increased 4-fold. No detectable amount of fatty acids with 20 or more carbon atoms were synthesized in this morphologically mature tissue, and the proportions of newly synthesized fatty acids more closely resembled the endogenous fatty acids in the immature tissue.Only 4% of the newly synthesized fatty acids were 18: 3 but most of this was incorporated into monogalactolipid. In the distal sections, 20 to 25% of the newly synthesized fatty acids in monogalactolipid were 18: 3 compared with the endogenous proportions of 85%. The differences in the composition of the newly synthesized fatty acids and the endogenous fatty acids appear to be related very largely to the low rate of 18: 3 biosynthesis from 18: 1 and 18: 2. Phosphatidyl choline and phosphatidyl ethanolamine, with lower proportions of 18: 3, contained radioactive fatty acids which resembled the endogenous composition more closely.Phosphatidyl choline was quantitatively the most important acyl lipid synthesized under both light conditions. In addition, there was considerable stimulation of acetate incorporation into phosphatidyl glycerol and monogalactolipid, especially in the morphologically most mature regions of the tissue at the higher light intensity.

Incorporation de glycérol et des acides palmitique, linoléique et arachidonique marqués dans les lipides hépatiques chez le rat

Summary Male adult rats, fasted for 18 hours were intravenously injected with 0,5 ml of saline containing labelled glycerol and a radioactive fatty acid. Three types of experiments were performed according to the nature of the injected fatty acid (palmitic or linoleic or arachidonic acids). Rats were killed 10, 30, 60 and 180 min. after the injection. The incorporation of glycerol and fatty acids into liver glycerolipids was measured. Fatty acids were quickly incorporated into triglycerides especially arachidonic acid while palmitic and linoleic acids were mainly localized in the phospholipid fraction. In all types of experiments, the incorporation of glycerol was lower than that of fatty acids. Therefore, the greater the incorporation of exogenous fatty acid, the higher were the amounts of exogenous glycerol in glycerolipids. In addition, the incorporation of glycerol into triglycerides and lecithins of different degrees of insaturation was also dependent on the injected fatty acid.

The metabolism of glucose, acetate, lipids and amino acids in lactating dairy cows

SUMMARYSpecialized techniques, previously used in surgically prepared goats, which simultaneously measure udder metabolism (arteriovenous difference of milk precursors x udder blood flow) and the whole body turnover of the milk precursors, have been successfully transferred to dairy cows. Methods of obtaining representative samples of arterial and mammary venous blood and of measuring udder blood flow are described.The rates of entry into the circulation, as determined by isotope dilution, of glucose, acetate and plasma free fatty acids were 3·3–4·0, 1·7–2·1 and 0·5 kg/day respectively. Acetate and glucose contributed 32–50 and 4–11% respectively of the total CO2output by the animal.Measurement of the uptake of precursors of milk constituents and their transfer into milk showed that there were substantial arteriovenous differences of glucose, acetate, triglyceride and β-hydroxybutyrate which were not significantly different between breeds or related to milk yield. Isotopic and balance data confirm that glucose is the main precursor of lactose and that the oxidation and transfer of glucose into lactose accounted for 69–98% of the glucose entry rate. As in the goat, plasma triglycerides and blood acetate accounted for 35–80% and 25–50% of the milk triglycerides respectively. Propionate was extracted from plasma but the uptake was only about 8% of the value for acetate.There was no net arteriovenous difference of phospholipids, cholesterol esters or free fatty acids, but the fall in specific radioactivity of free fatty acids across the mammary gland indicated there was an exchange of free fatty acids between plasma and mammary tissue. In agreement with previous findings, acetate contributed to all the milk fatty acids up to a chain length of C14and part of the C16fatty acid. Plasma triglycerides contributed to the remainder of the C16 fatty acid and all the milk fatty acids with a chain length of C18or higher.In contrast to the lactating goat, cow plasma contained very few chylomicrons. The majority of the triglycerides taken up by the udder were derived from the lowdensity lipoprotein fraction.The essential amino acids were extracted from blood in amounts sufficient to account for the essential amino acids secreted into milk protein. Although the plasma level of methionine was low, 52–72% of the material reaching the mammary gland was taken up. The uptake of arginine was far in excess of the requirement for milk protein synthesis.

Regulation of fatty acid biosynthesis in the hydrocarbon oxidizing microorganism, Acinetobacter sp.

1. The regulation of fatty acid biosynthesis was studied inAcinetobacter strainHOl-N, a microorganism which grows on long chain paraffinic hydrocarbons. Dual-label experiments with acetate-3H and palmitate-1-14C were designed to assess the differences in fatty acid metabolism between hexadecane-and acetategrown cells: 2. Experiments involving non-growing conditions indicated a preferential labeling of the cellular lipids with acetate-3H in acetate-grown cells and palmitate-1-14C in hexadecane grown cells. In addition to this relationship, non-growing cells assimilated exogenous lipid precursors (acetate) or preformed lipid (palmitate) almost exclusively into the cellular neutral lipids. 3. Under growing conditions acetate-grown cells exhibited a transfer of lipid radioactivity from the neutral lipid fraction to the phospholipid fraction. 4. Hexadecane-grown cells preferentially labeled with palmitate-1-14C in the cellular lipid exhibited a 98–100% loss of neutral lipid radioactivity. 5. Palmitate derived directly from hexadecane oxidation diluted the radioactive free fatty acid pool 4 times faster in hexadecane-grown cells than in acetate-grown cells. 6. These results indicate that cells grown at the expense of hexadecane are characterized by mechanisms more efficient in the transport and assimilation of exogenous fatty acid and thatde novo fatty acid biosynthesis is significantly reduced in hexadecane-grown cells.

Incorporation of acetate into fatty acids and complex lipids of soybean cotyledon slices under aerobic and anaerobic conditions

AbstractSoybean slices incubated with [1‐14C] acetate in the presence of air synthesized fatty acids to a greater extent than did slices in the absence of air. The proportion of radioactive fatty acids incorporated into the neutral lipid was ca. 35% in the presence or absence of air. However, both the proportion and the absolute amount of radioactive fatty acids in phospholipids were greater in the presence of air. This difference was particularly great in phosphatidic acid and in a minor uncharacterized phospholipid component. Significant incorporation of acetate into monoenoic acids was observed in these two lipids and in phosphatidyl choline. The latter also showed an accumulation of newly synthesized polyenoic acids when air was present. Stearic acid synthesis was greater under aerobic than under anaerobic conditions. The present results support the concept that a relationship exists between the synthesis of unsaturated fatty acids and their incorporation into phospholipids in plants.

Compartmentation of Glycerides in Adipose Tissue Cells: I. THE MECHANISM OF FREE FATTY ACID RELEASE

Isolated adipose tissue cells were prelabeled by incubation with radioactive fatty acids or radioglucose and subsequently transferred to a medium containing serum albumin and epinephrine. The specific activity of the fatty acids released during the first 15 min exceeded that of the bulk glycerides by a factor of over 10, and then dropped rapidly. Cellular free fatty acids could be excluded as the source of these high activity fatty acids. The specific activity of the diglyceride fraction in the prelabeled cells was 3 times that of the fatty acid released and dropped considerably during incubation with epinephrine. The absolute amount of diglyceride did not decrease. Diglycerides accounted for part of the fatty acids released. The rest was derived from a pool of triglycerides of high specific activity, which replenished the diglyceride pool and equilibrated with the bulk triglycerides in 1 hour. Equilibration of the triglyceride pools was very slow in the absence of epinephrine.

Selective Acylation of 1-Acylglycerophosphorylinositol by Rat Brain Microsomes: COMPARISON WITH 1-ACYLGLYCEROPHOSPHORYLCHOLINE

Rat brain microsomes were shown to acylate 1-acylglycerophosphorylinositol (1-acylGPI) when incubated with radioactive fatty acids, ATP, CoA and MgCl2, or with chemically synthesized acyl esters of CoA. Both acylation systems showed a concentration dependence on added lysolipid acceptor and free fatty acids, cofactors, or CoA esters. With free fatty acids, relative acylation rates varied with concentration of lysolipid; at low levels arachidonate, linoleate, and oleate were superior to palmitate and stearate, but at higher levels the differential was greatly reduced. With CoA esters, acylation of 1-acylGPI was determined either spectrophotometrically or by measuring radioactivity incorporated from 14C- or 3H-labeled acyl-CoA. The radioassay showed that a large proportion of acyl groups was incorporated into polyphosphoinositides, principally phosphatidylinositol phosphate, as well as phosphatidylinositol, possibly as a result of the concerted action of acyltransferase and membrane-bound phosphatidylinositol kinase. Acylation rates were much higher with acyl-CoA esters than with free fatty acids and cofactors. The most striking feature was that rates with arachidonoyl-CoA were 2 to 5 times higher than with linoleoyl-, linolenoyl-, or eicosatrienoyl-CoA and 5 to 10 times higher compared with oleoyl- and docosahexaenoyl-CoA. Positional analysis of the labeled products with snake venom phospholipase A2 showed that unsaturated acyl groups were incorporated almost exclusively into the 2-position of inositol lipid but 25 to 30% of radioactivity from palmitoyl- and stearoyl-CoA appeared in the 1-position, indicating that some isomerization of the lysolipid acceptor had occurred. Maximal acylation of 1-acylglycerophosphorylcholine (1-acylGPC) occurred under conditions similar to that for the inositol lipid, but a somewhat different selectivity was shown. Acylation rates with 1-acylGPC were the same or higher than for the inositol lipid except with arachidonoyl-CoA, where the rate with 1-acylGPI was 2 to 3 times higher than with 1-acylGPC. It is suggested that the acylation of 1-acylGPI constitutes an important and highly selective mechanism for achieving the strict species specificity exhibited by inositides in rat brain. The marked difference in acylation rates between arachidonoyl-CoA (20:4, n-6) and eicosatrienoyl-CoA (20:3, n-6) indicates that the double bond between carbons 5 and 6 may be critical in directing enzyme selectivity for arachidonoyl-CoA.

Growth effects on the insulin alteration of chang liver fatty acid metabolism

The effect of insulin on the free fatty acid metabolism of Chang liver cells was observed to vary, depending on the growth rates of the cells. When the cells were not actively growing, insulin modestly increased the total recovery of radioactive fatty acid in lipid and produced a major increment of fatty acid in cellular triglyceride. During logarithmic growth of the cells these insulin changes were much less pronounced.

Synthesis of fatty acid esters of short-chain alcoh an acyltransferase in rat liver microsomes

Ethyl esters of fatty acids have been identified as the product formed when rat liver microsomes were incubated in the presence of ethanol, radioactive fatty acids, CoA, ATP, and Mg 2+ . Ag + thin-layer chromatography and preparative gas-liquid chromatography were used to identify the product. The biosynthesis of ethyl esters was optimal at a pH near 8. Other primary short-chain alcohols were also esterified and the K m for the alcohol decreased with increasing chain length from methanol to hexanol.

The oleyl-coenzyme-A desaturase of potato tubers. Enzymatic properties, intracellular localization and induction during "aging" of tuber slices.

An active oleyl‐coenzyme‐A desaturase was associated with a microsomal fraction from “aged” slices of potato tuber; starting from [1‐14C]oleyl‐coenzyme A as a substrate, in vitro, more than 40% of the final fatty acid radioactivity was recovered in linoleic acid, the most abundant fatty acid of the intracellular membranes of potato tubers. The presence of serum albumin in the reaction mixture was essential for the desaturation reaction and for preventing the degradation of polyunsaturated fatty acids. This stabilization of the desaturase activity by serum albumin allowed a great resistance upon freezing. The microsomal oleyl‐coenzyme‐A desaturase showed a pH optimum around 7.0–7.2 and a temperature optimum near 25°C. The apparent Km of the desaturase for oleyl‐coenzyme A was 25 μM. Oxygen and pyridine nucleotide were required for oleyl‐coenzyme A desaturation (NADH or NADPH were found nearly equally effective in the desaturation). Although NADPH was more effective than NADP, NAD was a effective as NADH for desaturation, suggesting that a NADH‐regenerating system probably exists in the microsomal suspension. The oleyl‐coenzyme‐A desaturase was specific in vitro for oleyl‐coenzyme A as a substrate; no desaturation was observed with ammonium oleate, which was, however, desaturated in vivo by aged slices of potato tuber. Oleyl‐coenzyme A (and the newly labelled linoleic acid molecules) were essentially incorporated into phospholipids and particularly phosphatidylcholine. The oleyl‐coenzyme‐A desaturase was almost entirely associated with the microsomal membranes, as shown by differential centrifugation and sucrose‐gradient separations. The oleyl‐coenzyme‐A desaturase activity (absent in the freshly cut slices) was induced during the aging of slices; a linear increase with the time of aging was found in many microsomal activities, such as oleyl‐coenzyme A desaturase, NADH‐cytochrome c reductase and protein synthesis. The inhibition of all these events by cycloheximide, or the partial inhibition by actinomycin D indicated that derepression of the genetic activity and synthesis of new proteins were involved in the induction of the oleyl‐coenzyme‐A desaturase.

The contribution of lipogenesis in situ to the accumulation of fat by rat adipose tissue

The purpose of this study was to assess the contribution of lipogenesis in situ for the accumulation of fat by the adipose tissue of rats. [U- 14C] Glucose was injected into animals that had been fed diets containing increasing amounts of corn oil. Under these conditions the recovery of labelled fatty acids from the adipose tissue of the animals fed diets containing 4 and 9% corn oil was significantly decreased. On the other hand, when the adipose tissue of these animals was incubated in vitro in the presence of [U- 14C] glucose, the synthesis of labelled fatty acids was significantly increased. Increasing amounts of dietary fat did not alter the adipose tissue lipoprotein lipase activity. Under these conditions the uptake of labelled triglyceride fatty acids by the adipocytes of rats fed fat is probably very limited when compared with the uptake by the adipocytes of rats fed on a fat-free diet. In the liver of the animals fed fat the synthesis of labelled fatty acids was decreased both in vitro and in vivo. By reducing the in vivo lipogenesis by the liver the amount of labelled triglyceride fatty acids of hepatic origin secreted into the plasma was also reduced. It is argued, therefore, that in the animals fed on a fat-free diet the radioactivity recovered in the adipose tissue fatty acid fraction can probably be credited to synthesis in situ and uptake of plasma triglyceride fatty acids, while in the adipose tissue of the animals fed on a high-fat diet the radioactive fatty acids recovered in the adipose tissue can be credited mainly to synthesis in situ.

Positional distribution and turnover of fatty acids in phosphatidic acid, phosphoinositides, phosphatidylcholine and phosphatidylethanolamine in rat brain in vivo

1. 1. Experiments were designed to examine the possible relation between fatty acids of phosphatidic acid and the phospholipids derived from phosphatidic acid in rat brain in vivo. After intracerebral injection of radioactive fatty acids, distribution studies revealed that the enzymes for phosphatidic acid synthesis in brain were selective with respect to placement of the major saturated and polyunsaturated fatty acids. Thus, stearate and palmitate were incorporated preferentially into the 1-position and arachidonate almost exclusively into the 2-position. Oleate and linoleate were almost equally divided between both positions. 2. 2. The uptake of [ 3H]arachidonate by phosphatidylcholine and monophosphoinositide was very rapid and exceeded that by phosphatidic acid. Incorporation into phosphatidylethanolamine was less and appeared to be biphasic. Double-label ratios from simultaneously injected [ 3H]arachidonate and [ 14C]glycerol suggested that the rapid incorporation of arachidonate resulted from acyl-exchange reactions independent of de novo synthesis. Double-label ratios of di-and triphosphoinositides were much lower than monophosphoinositide, indicating there was a compartment of monophosphoinositide, highly labelled with arachidonate, that did not equilibrate with the polyphosphoinositides. 3. 3. A sequential transfer of stearoyl groups from phosphatidic acid to other phospholipids was indicated, since incorporation of [ 3H]stearate into phosphatidic acid preceded that into monophosphoinositide, phosphatidylcholine and phosphatidylethanolamine. However, double-label experiments with [ 14C]glycerol suggested that a fraction of the stearoyl groups may be turning over by acyl-exchange reactions. 4. 4. I-Acyl lysophosphatidylcholine, labelled with [ 3H]stearate and [ 14C]glycerol, injected intracerebrally, was incorporated intact into diacyl phosphatidylcholine, confirming that direct acylation of lysointermediates could occur in brain. I-Acyl lysomonophosphoinositide was degraded rapidly and there was no significant conversion to diacyl lipid.

In vivo and in vitro metabolism in hypothalamic obesity.

U-14C-Glucose was injected into weanling rats two weeks after electrolytic destruction of the ventromedial hypothalamic nuclei. Incorporation of radio-activity into plasma lipids as well as liver, adipose tissue, diaphragm and carcass glycogen, total lipid and saponifiable fatty acids was measured. On a fat free as well as on a chow diet, rats with lesions incorporated more radioativity into all adipose tissue components and into liver fatty acids but not into liver glycogen. On the fat containing diet (chow) radioactivity of plasma lipid was increased and that of liver total lipid unchanged, whereas on a fat-free diet incorporation into plasma lipid was not increased while that into liver lipid was. Diaphragm total lipid and fatty acid radioactivity was increased while that of diaphragm glycogen was not. Carcass lipid, fatty acid and glycogen radioactivity were increased. — Diaphragm was also incubatedin vitro with U-14C-Glucose or 1-14C-Palmitate. Glucose incorporation into total lipid and fatty acid was increased whereas oxidation and incorporation into glycogen were not. Palmitate oxidation and incorporation into phospholipid were decreased while incorporation into triglyceride was increased. - Results have been discussed in the light of similar changes previously noted with adipose tissuein vitro.

Stearyl CoA as a precursor of oleic acid and glycerolipids in mammary microsomes from lactating bovine: possible regulatory step in milk triglyceride synthesis.

AbstractThe stearyl desaturase of lactating bovine mammary tissue is located in the microsomes and requires activated fatty acid and NADH for activity. Other enzymes, acyl‐transferase(s) and deacylase which apparently compete with the desaturase for substrate are also present. Both the substrate 1‐14C‐stearyl CoA and the oleic acid produced by desaturase are esterified into the various lipid classes. The oleic acid is preferentially acylated into positionsn‐3 of the triglycerides andsn‐2 of the phosphatidylcholine. Experimental conditions causing reduced desaturase activity depressed triglyceride synthesis, and stimulation of desaturation by NADH L−α GP, acidic pH, 5.6, was accompanied by increased incorporation of radioactive fatty acids into the triglycerides. These data indicated that desaturase and glyceride acyl transferase were located contiguously within the microsomal membranes. The possibility that desaturase activity might control triglyceride synthesis in vivo is discussed. It was observed that mammary tissue from nonlactating cows 1–2 weeks and 2 days prior to calving lacked or possessed very low stearyl desaturase activity.

An improved method for collection and measurement of radioactivity in compounds separated by gas—liquid chromatography

14C-Labeled compounds in the effluent of a gas—liquid chromatograph were collected intact by condensation and adsorption to small glass beads coated with silicone fluid in short glass cartridges and then eluted into scintillation vials for counting. The overall recovery of radioactive fatty acid methyl esters and trimethylsilyl derivatives of glycerol and glucose was greater than 90%.

Effect of free fatty acid structure on binding to rat liver mitochondria

We have compared the binding of seven long-chain free fatty acids to rat liver mitochondrial suspensions. Bovine serum albumin was present in the incubation medium, and the fatty acid-albiumin molar ratio was varied between 0.5 and 5.5. A steady-state amount of radioactive fatty acid was recovered from the mitochondria after 2 min of incubation at 23°. Most of the fatty acid uptake was due to transfer from albumin to the mitochondria, not incorporation of the intact fatty acid-albumin complex. Uptake of the saturated fatty acids increased as the chain length increased: lauric < myristic < palmitic < stearic. Saturated fatty acids of a given chain length were taken up to a greater extent than the corresponding unsaturated fatty acids: palmitate > palmitoleate; stearate > oleate or linoleate. Almost all of the newly incorporated fatty acid was bound reversibly in unesterified form and was associated with the mitochondrial membranes. These findings suggest that the differences in uptake of the various free fatty acids result at least partly from differences in binding to the mitochondrial membranes.

The pattern of fatty acid synthesis in lactating rabbit mammary gland studied in vivo.

The biosynthesis of fatty acids has been studied in lactating rabbits at 6h after intravenous injection of sodium [1-(14)C]acetate. The specific radioactivities of the individual fatty acids (C(6:0) to C(14:0)) and the proportions of these fatty acids synthesized were similar in mammary tissue and milk. Hexanoic acid had the highest specific radioactivity, and the C(8:0)-C(14:0) fatty acids had similar specific radioactivities, which were about five times those of C(16) and C(18) acids. No radioactivity was detected in fatty acids of chain length <C(14) in the liver, blood or adipose tissue and the specific radioactivities of fatty acids of chain length >C(14) in these tissues were similar to those of the long-chain fatty acids in the milk and mammary gland. The results show that the C(4:0)-C(14:0) fatty acids are synthesized within the mammary gland rather than by fatty acid uptake from circulating blood or by oxidation of long-chain fatty acids within the gland. We conclude that de novo synthesis of esterified fatty acids in vivo by this tissue has a high degree of chain-length specificity.

Changes in fatty acid metabolism after erythrocyte peroxidation: stimulation of a membrane repair process.

To study certain membrane repair processes in human erythrocytes, vitamin E-deficient cells were incubated with hydrogen peroxide. The incorporation of exogenous fatty acid and the transfer of fatty acid from phosphatidylcholine and neutral lipid into phosphatidylethanolamine were examined using radioactive fatty acids. Hydrogen peroxide stimulated the incorporation of fatty acid into all membrane phospholipids. The specific activity of phosphatidylethanolamine was increased disproportionately. The lipids of the membranes of erythrocytes were labeled with saturated and unsaturated fatty acid. When these erythrocytes were subsequently incubated with hydrogen peroxide, both types of fatty acid were transferred from superficial erythrocyte neutral lipids into phosphatidylethanolamine. However, the unsaturated fatty acids of phosphatidylethanolamine were subsequently altered by hydrogen peroxide, whereas the saturated fatty acids were not. The cumulative effect of these processes was a relative decrease in unsaturated fatty acid and an increase in saturated fatty acid in the phosphatidylethanolamine of the erythrocyte membrane. The net effect of these events represents the operation of repair processes which distort the usual fatty acid composition of erythrocyte membranes in the presence of H(2)O(2). This distortion may contribute to membrane permeability changes which occur during peroxide exposure and which precede the eventual hemolysis of these cells.