Remodeling of rat hepatocyte phospholipids by selective acyl turnover

Acyl turnover of rat hepatocyte phospholipids and triacylglycerols was assessed by incubating the cells in media containing 40% H2(18)O and measuring the time-dependent incorporation of 18O into ester carbonyls by gas chromatography-mass spectrometry of hydrogenated methyl esters. Incorporation of 18O into 22-carbon acyl groups was low in phosphatidylcholine, phosphatidylinositol, and phosphatidylserine, whereas in phosphatidylethanolamine, it was about the same as in the other acyl groups. Incorporation of 18O into individual molecular species of phosphatidylcholine and phosphatidylethanolamine was determined after phospholipase C hydrolysis, derivatization to dinitrobenzoates, and separation by high-performance liquid chromatography. In most molecular species, acyl groups at the sn-1 and sn-2 positions became 18O-labeled at drastically different rates, indicating remodeling through deacylation-reacylation. Molecular species expected to arise de novo from acylation of glycerophosphate exhibited similar rates of 18O incorporation at the sn-1 and sn-2 positions. The data suggest that hepatocyte phospholipids are continually synthesized, remodeled by deacylation-reacylation at specific turnover rates up to 10-15%/h, and degraded. This acyl turnover probably does not involve the majority of intracellular unesterified fatty acids whose 18O incorporation was found to be very low. In contrast, the oxygens of extracellular unesterified fatty acids were readily exchanged with the media. This exchange was enzyme-catalyzed, possibly by lipases released into the media from damaged cells. Incorporation of 18O into exogenously added fatty acids was also rapid and resulted in enhanced uptake of 18O-labeled fatty acids into cellular lipids, primarily triacylglycerols and phosphatidylcholine, without drastic change of the intracellular free fatty acid pool.     

The incorporation of unsaturated fatty acids of the n-9, n-6, and n-3 families into individual phospholipids by isolated hepatocytes of thermally-acclimated rainbow trout, Salmo gairdneri

Rates of incorporation of 1-14C-oleic (18:1n9), -linoleic (18:2n6), and -linolenic (18:3n3) acids into individual phosphatides were determined in isolated hepatocytes from cold (5 degrees C)- and warm (20 degrees C)-acclimated rainbow trout, Salmo gairdneri. Fatty acid incorporation into phosphatidylcholine (PC) exceeded that into all other phospholipids, but at assay and acclimation temperatures of 5 degrees C, incorporation into phosphatidylethanolamine (PE) was generally intermediate between that of PC and the remaining phosphatides. Specific radioactivities (ratios of percentage isotope incorporation-to-mole percentage of phosphatide) were consistently less than one for both PC and PE, and greater than one for phosphatidic acid (PA), lysophosphatidylcholine (LPC), phosphatidylserine (PS), and cardiolipin (CL). For PS, specific radioactivities were greater in cold- than warm-acclimated trout, and greater at 5 degrees C than 20 degrees C. Rates of oleate incorporation were generally higher, and rates of incorporation of 18:2 and 18:3 lower in cold- than warm-acclimated trout. Most phospholipids demonstrated a clear preference for the incorporation of 18:2 when assayed at 20 degrees C; however, at 5 degrees C the incorporation of 18:2 was reduced and 18:3 was generally the preferred substrate. A reduction in assay temperature from 20 degrees C to 5 degrees C also shifted the incorporation of 18:2 away from PC into PS and PA. These data were interpreted to indicate 1) a cold-induced activation of PS metabolism, possibly resulting in elevated levels of PE; 2) lower rates of general acyl group turnover in animals acclimated to 5 degrees C than 20 degrees C; 3) a specificity to the acclimation response that favors the incorporation at cold temperatures of polyunsaturated fatty acids, but not the parent acids from which they are derived; and 4) the participation of a deacylation-reacylation cycle in the metabolism of phospholipids, particularly at cold temperatures.     

Reactivities of highly unsaturated fatty acids for the hydrogenation on nickel catalyst

The reactivities of the C₂₀ highly unsaturated fatty acids (20:5, 20:4, 20:3 etc.…) during heterogeneous hydrogenation on nickel catalyst have been studied using a computer program. Three parameters are required to determine the hydrogenation rate constant of the different fatty acid classes; the C₂₀ fatty acid composition of the starting oil, the C₂₀ fatty acid composition of a partially hydrogenated oil (PHO) and the time of reaction. It is shown that, in order to minimize the experimental errors, the PHO must be selected in such a way that the induction period is over and that this oil still contains appreciable amounts of 20:5 and 20:4.Very little difference was found for the reactivities of the 20:5, 20:4 and 20:3 acids. The major difference among unsaturated fatty acids was found to be between the 20:2 and 20:1 isomers for a hydrogenation effected according to common commercial practices.The computer program is a general one also useful for the prediction of the fatty acid composition of slightly hydrogenated oils, but is not suitable for oils hydrogenated to very low iodine values, or for those containing high proportions of trans fatty acids.     

Discontinuous thermotropic response of Tetrahymena membrane lipids correlated with specific lipid compositional changes

Steady-state fluorescence polarization measurements of 1,6-diphenyl-1,3,5-hexatriene in microsomal lipids from Tetrahymena pyriformis cells grown at 39 or 15°C revealed discrete slope discontinuities in plots of polarization vs. temperature. Two well-defined ‘break points’ were present in the 0–40°C temperature range examined and their precise location was dependent upon the growth temperature of the cells. By mixing phospholipids from cells grown at different temperatures, the break points at 17.5 and 32°C in 39°C-lipid multilayer preparations were shown to correlate with the breaks at 12 and 27°C, respectively, in similar preparations from 15°C-grown cells. The discrete break points were also present, but at slightly different characteristic temperatures, in a phosphatidylcholine fraction and a phosphatidylethanolamine plus 2-aminoethylphosphonolipid fraction purified from the phospholipids and in total microsomal lipids (phospholipids plus the sterol-like triterpenoid, tetrahymanol). However, catalytic hydrogenation of the phospholipid fatty acids or mixing the non-hydrogenated phospholipids with increasing proportions of synthetic dipalmitoyl phosphatidylcholine eliminated the break points. We interpret this discontinuous thermotropic response in microsomal lipids as signalling a lipid phase separation of importance in regulating physiological events.     

Modulation of chloroplast membrane lipids by homogeneous catalytic hydrogenation

A method is reported for the modification of lipids in situ in chloroplast membrane by which a homogeneous, water-soluble catalyst Pd(QS)2 (QS, sulphonated alizarine; C14H6O7NaS) is incorporated into the thylakoids of isolated chloroplast. The catalyst itself did not affect the photosynthetic activity but caused an extensive loss of unsaturated fatty acids in the presence of hydrogen gas. The polyunsaturated fatty acids were hydrogenated at a faster rate than the monoenoic acids. During hydrogenation the orientational ordering of membrane lipids, as measured with the C-12 positional isomer of spin-labelled stearic acid, displayed a slight increase in agreement with the alterations in membrane composition. Progressive saturation of double bonds of lipids primarily inhibits electron transport between the photosystems followed by the inhibition of electron flow around photosystem II. Photosystem I electron transport was not inhibited even by 50% fatty acid hydrogenation. We suggest that using Pd(QS)2 catalyst for thylakoid hydrogenation offers an excellent technique to study the role of various unsaturated fatty acids in the regulation of membrane fluidity and photosynthetic processes.     

Effect of catalytic hydrogenation of Tetrahymena ciliary phospholipid fatty acids on ciliary phospholipase A activity

Detached Tetrahymena cilia were treated for increasing periods of time with the homogeneous hydrogenation catalyst palladium di(sodium alizarine monosulphonate). This caused a 4-70% reduction in the number of double bonds in phospholipid-bound fatty acids and a concurrent decrease in membrane fluidity as detected by ESR measurements. Ciliary phospholipase A activity was markedly inhibited when as little as 13% of the fatty acid double bonds had been hydrogenated, suggesting that the enzyme activity is very sensitive to changes in membrane fluidity.     

Hepatic lipase-mediated hydrolysis versus liver uptake of HDL phospholipids and triacylglycerols by the perfused rat liver

Hepatic triacylglycerol-lipase-mediated hydrolysis and liver uptake of high-density lipoprotein (HDL) lipid components were studied in a recirculating rat liver perfusion, a situation where the enzyme is physiologically expressed and active at the vascular bed. Human native HDL were labelled with tri-[3H]oleoylglycerol, [N-methyl-3H]dipalmitoylphosphatidylcholine (DPPC), 1-palmitoyl,2-[14C]linoleoylphosphatidylcholine (PLPC), 1-palmitoyl,2-[14C]linoleoylphosphatidyl-ethanolamine (PLPE) and 1-palmitoyl,2-[14C]palmitoylphosphatidylethanolamine (DPPE). (1) Relative degradation rates of phosphatidylethanolamine molecular species were 2- to 10-fold higher than those of phosphatidylcholine. Considering [14C] PLPC and [14C] PLPE as representative of HDL phosphatidylcholine and phosphatidylethanolamine, respectively, the amounts of lysophosphatidylcholine and lysophosphatidylethanolamine generated after a 60 min perfusion were comparable. The enzyme showed a clear preference for the molecular species bearing an unsaturated fatty acid at the 2 position of glycerol; this was the most pronounced in the case of phosphatidylethanolamine molecular species. (2) Relative liver uptake of HDL-phosphatidylethanolamine was 4- to 5-fold higher than that of HDL-phosphatidylcholine, irrespective of the constitutive fatty acids. Nevertheless, mass estimation indicated that 3 times more molecules of phosphatidylcholine than of phosphatidylethanolamine were transferred. No correlation could be found between the relative degradation rates of phospholipids and their relative liver uptake, indicating a dissociation between the two processes. (3) Perfusate decay and relative liver uptake of labelled HDL-triacylglycerol were higher than that of any phospholipid class. No circulating radiolabelled free fatty acids accumulated in the perfusate, but they were found acylated into liver cell phospholipids and triacylglycerols. (4) A prior 10-12-min washout of the liver vascular bed with heparin removed over 80% of the hepatic lipase activity, as assessed by specific immunoinhibition. Hepatic lipase-depleted liver displayed impaired phospholipid hydrolysis and triacyglycerol uptake, whereas the transfer of HDL phospholipids to liver tissue was unaffected.     

Relationship between lipid composition, frequency of ethanol-induced respiratory deficient mutants, and ethanol tolerance in Saccharomyces cerevisiae

The frequency of ethanol-induced respiratory deficient mutants and lipid composition in two Saccharomyces cerevisiae strains showing different degrees of ethanol tolerance were investigated. The more ethanol-tolerant strain exhibited a lower frequency of ethanol-induced respiratory deficient mutants than the less ethanol-tolerant strain. In addition, the more ethanol-tolerant strain contained a higher ergosterol/phospholipid ratio, a higher proportion of phosphatidylcholine, a lower proportion of phosphatidylethanolamine, a higher incorporation of long-chain fatty acids in total phospholipids, and a slightly higher proportion of unsaturated fatty acids in total phospholipids than the less ethanol-tolerant strain. These results show a clear relationship between the lipid composition, the frequency of ethanol-induced respiratory deficient mutants, and the ethanol tolerance of S. cerevisiae. A possible explanation of this relationship is discussed.     

The release of radioactive arachidonate from lipids of red blood cells during prolonged incubations in vitro

Red blood cells were isolated from rat blood and incubated in the presence of [3H]arachidonate. A sizeable quantity (18%) of the radioactivity was incorporated into red cell lipids, of which phosphatidylcholine was the most highly labelled. Radioactive arachidonate was found at position 2 of this phospholipid. Free fatty acids were removed by washing the cells in solutions containing fatty-acid-free bovine serum albumin. The labelled red cells were then incubated for up to 16 h at 37 degrees C. After 16 h of incubation in saline-buffer-glucose or rat serum, 20 and 26%, respectively, of the total radioactivity was found in free fatty acids, and there were corresponding declines in the percentage radioactivities found in phosphatidylcholine. In the presence of serum, there was a more rapid release of radioactive fatty acid over the 2- to 16-h time course. There was not a significant drop in the phosphate levels of the total red cell phospholipids or phosphatidylcholine after 16 h of incubation and, as a result, there were large declines in the specific radioactivities of phosphatidylcholine. Diacylglycerols were not highly labelled and the action of phospholipase A2 on labelled phosphatidylcholine was indicated. When white blood cells were added to labelled red cells, there was little evidence of white cell involvement in the release of radioactive fatty acid, suggesting that the red cells themselves may be involved in arachidonate release. Red cells may serve as sources of arachidonate, released following hemorrhage in brain and metabolized to form various biologically active eicosanoids.     

Incorporation into phospholipid classes and metabolism via desaturation and elongation of various 14C-labelled (n-3) and (n-6) polyunsaturated fatty acids in trout astrocytes in primary culture

The incorporation and metabolism of [1-14C]18:3(n-3), [1-14C]20:5(n-3), [1-14C]18:2(n-6), and [1-14C]20:4(n-6) were studied in primary cultures of trout brain astrocytes. There were no significant differences between the amounts of individual fatty acids incorporated into total lipid at 22 degrees C, with greater than 90% of all the fatty acids being incorporated into polar lipid classes. The distributions of 18:2(n-6), 18:3(n-3), and 20:5(n-3) in individual phospholipid classes at 22 degrees C were very similar, with 57-63 and 18-24% being incorporated into phosphatidylcholine and phosphatidylethanolamine, respectively. Approximately equal amounts of 20:4(n-6), approximately 30% of the total, were incorporated into each of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. The metabolism of the (n-3) fatty acids to longer-chain and more unsaturated species was significantly greater than that of (n-6) acids, but delta 4-desaturase activity was very low. A culture temperature of 10 degrees C increased the incorporation of all the fatty acids into total lipid and that of C20 fatty acids into polar lipid. At 10 degrees C, the incorporation of C20 fatty acids into phosphatidylethanolamine and phosphatidylinositol was increased, and the incorporation into phosphatidylcholine and phosphatidylserine was decreased. The distribution of C18 fatty acids was unchanged at the lower temperature, as was the desaturation and elongation of all the polyunsaturated fatty acids incorporated.     

Changes in lipid fluidity and fatty acid composition with altered culture temperature in Tetrahymena pyriformis-NT1

Cultures of T. pyriformis-NT1 were grown at 20 degrees C (Tg 20 degrees C) and 38 degrees C (Tg 38 degrees C). G.L.C. analysis and D.P.H. fluorescence polarization measurements in extracted phospholipids indicated that there was increased saturation of fatty acids and relatively reduced fluidity as growth temperature was increased. Breakpoints occurred in the Arrhenius plots of fluorescence polarization at 16 degrees C for Tg 38 degrees C total extracted phospholipids and 9 degrees C for Tg 20 degrees C lipids.     

Alteration of fatty acid composition of LM cells by lipid supplementation and temperature.

Alteration of the fatty acid composition of monolayer cultures of LM cells grown in chemically defined medium was achieved by supplementation with fatty acids complexed to bovine serum albumin. Phospholipids containing up to 40% linoleate were found in cells grown in medium containing 20 mu g of linoleate/ml. Incorporation of linoleate into phospholipids reached a plateau after 12-24 hr, and cells remained viable for at least 3-4 days. Although linoleic, linolenic, and arachidonic acids were incorporated into LM cells equally well, only the latter was elongated by these cells under these experimental conditions. Nonadecanoic acid was incorporated to a lesser extent than the polyunsaturated fatty acids. Phosphatidylcholine and phosphatidylethanolamine of LM cells had different fatty acid compositions; phosphatidylethanolamine contained more longer chain and unsaturated fatty acids. Cells were also grown in the absence of choline and presence of choline analogs such as N,N-dimethylethanolamine, N-methylethanolamine, 3-amino-1-propanol, and 1-2-amino-1-butanol. The analog phospholipids in these cells had fatty acid compositions which were intermediate between those of phosphatidylethanolamine and phosphatidylcholine of control cells grown in the presence of choline. Linoleate was found in both phosphatidylcholine and phosphatidylethanolamine of cells supplemented with linoleate. The sphingolipid fraction of these cells, however, did not contain significant amounts of linoleate. When linoleate was present in the phospholipids, compensatory decreases in the oleate and palmitoleate content of phospholipids were observed. Lowering of the growth temperature to 28 degrees produced an increase in unsaturate fatty acid content of the phospholipids. When linoleate was supplied to cells grown at 28 degrees, there was no further increase in the unsaturated fatty acid composition of the phospholipids. Using both fatty acid supplementation and lowered growth temperature, LM cell membranes can be produced which have phospholipids with vastly different fatty acid compositions.     

Asymmetry of arachidonic acid metabolism in the phospholipids of the human platelet membrane as studied with purified phospholipases

Human platelets were incubated with high density lipoproteins (HDL) doubly labelled with either free [14C]arachidonate/[3H]arachidonoylphosphatidylcholine or free [14C]oleate/[3H]oleoylphosphatidylcholine. Whereas [14C]arachidonate was incorporated at a 10-15-times higher rate than [14C]oleic acid, the exchange of both species of phosphatidylcholine occurred to the same extent. In both cases, free 3H-labelled fatty acids were generated during the labelling procedure, indicating phospholipase A2 hydrolysis. A redistribution of radioactivity to other phospholipids was noted after exchange of [3H]arachidonoylphosphatidylcholine only. (2) The exchange of phosphatidylcholine to platelets was confirmed using [14C]choline-labelled dipalmitoyl-and 1-palmitoyl-2-arachidonoylphosphatidylcholines. (3) Non-lytic degradation of platelet phospholipids by phospholipases revealed that free fatty acids were incorporated at the inside of the cells, whereas exchange was taking place on the platelet outer surface. However, 2-arachidonoylphosphatidylcholine displayed a more rapid movement towards the cell inside. The above findings suggest a topological asymmetry for the two pathways (acylation and exchange) of fatty acid renewal in platelets. The possible mechanisms and physiological relevance of the translocation of the external arachidonic acid pool across the membrane are discussed.     

Chlorinated fatty acid distribution in Mycobacterium convolutum phospholipids after growth on 1-chlorohexadecane

The composition of phospholipids from Mycobacterium convolutum R22 was determined after growth at two temperatures (20 and 30 degrees C) with 1-chlorohexadecane as the substrate. Comparisons were made with the phospholipids of cells grown on n-hexadecane. Phosphatidylinositolmannosides and phosphatidylethanolamine (PE) were the major phospholipids in n-hexadecane-grown cells. In 1-chlorohexadecane-grown cells, phosphatidylinositolmannosides were approximately half of the total phospholipids, with lesser amounts of PE and cardiolipin (CL). The relative level of PE was greater at 20 degrees C (versus that at 30 degrees C) after growth on either substrate. A determination was made of structure and positional distribution of constituent fatty acid in both CL and PE. The relative amount of unsaturated fatty acid was higher at 20 degrees C. There were two C16:1 fatty acids (C16:1 delta 9 and C16:1 delta 11), and these had positional preferences in both CL and PE. The positional sites of chlorinated fatty acids differed in both CL and PE at the two temperatures. The results confirm that microorganisms can specifically distribute chlorinated fatty acids into cellular phospholipids.     

Chlorinated fatty acid distribution in Mycobacterium convolutum phospholipids after growth on 1-chlorohexadecane.

The composition of phospholipids from Mycobacterium convolutum R22 was determined after growth at two temperatures (20 and 30 degrees C) with 1-chlorohexadecane as the substrate. Comparisons were made with the phospholipids of cells grown on n-hexadecane. Phosphatidylinositolmannosides and phosphatidylethanolamine (PE) were the major phospholipids in n-hexadecane-grown cells. In 1-chlorohexadecane-grown cells, phosphatidylinositolmannosides were approximately half of the total phospholipids, with lesser amounts of PE and cardiolipin (CL). The relative level of PE was greater at 20 degrees C (versus that at 30 degrees C) after growth on either substrate. A determination was made of structure and positional distribution of constituent fatty acid in both CL and PE. The relative amount of unsaturated fatty acid was higher at 20 degrees C. There were two C16:1 fatty acids (C16:1 delta 9 and C16:1 delta 11), and these had positional preferences in both CL and PE. The positional sites of chlorinated fatty acids differed in both CL and PE at the two temperatures. The results confirm that microorganisms can specifically distribute chlorinated fatty acids into cellular phospholipids.     

Formation of omega- and (omega-1)-hydroxyfatty acids and plausible formation of ketofatty acid from microsomal phospholipids

Rat liver microsomes labeled with spin-labeled phosphatidylcholine release the label into the aqueous phase during the aerobic incubation with NADPH (Biochem. Biophys. Res. Commun. (1979) 87, 300-307). To establish the chemical nature of the released moiety, microsomes were labeled with [14C]phosphatidylcholine. When the 14C-labeled microsomes were incubated with NADPH under aerobic conditions, a few percent of the radioactivity was liberated into the aqueous phase within 60 min. Thin-layer chromatographic analysis of the radioactive substance liberated showed the presence of hydroxylated fatty acids derived from the 2-position of glycerol moiety. About one-third of the fatty acids formed from [14C]phosphatidylcholine during the incubation were converted into hydroxy-derivatives. Gas chromatography/mass spectrometry analysis further confirmed an NADPH-dependent formation of 16-hydroxypalmitic acid, 15-hydroxypalmitic acid, and hydroxy-derivatives of other fatty acids from the phospholipids of the microsomal membrane. Evidence was also obtained indicating the formation of ketopalmitic acid.     

Lipid hydrogenation induces elevated 18:1-CoA desaturase activity in Candida lipolytica microsomes.

Microsomal membranes prepared from the mesophilic yeast Candida lipolytica grown at 10 degrees C were hydrogenated by the homogeneous Pd-catalyst, palladium di (sodium alizarine sulfonate) (Pd(QS)2). After hydrogenation to various levels, the microsomes were washed free of the Pd-complex and transferred to a reaction mixture (containing NADH, MgCl2, ATP, CoA and [14C]18:1-CoA) for assay of 18:1-CoA desaturase activity. Microviscosity alterations were also followed by measuring changes in DPH fluorescence polarization. Rapid catalytic hydrogenation of unsaturated fatty acids of the lipids occurred within 20-120 s, resulting in large increases in 16:0, 18:0 and 18:1 acids and decreases in 18:2 acid. In the range 7-20% 18:0 content, a pronounced increase in desaturase activity was observed, with a maximum of greater than 2-fold at a 18:0 content of 12%, followed by a decrease to the initial activity at 33% 18:0 content. These changes were well-correlated with changes in microviscosity, maximal desaturase activity occurring in the DPH fluorescence anisotropy range of 0.23-0.24; above and below this range, desaturase activities were close to the initial control values. It is suggested that the hydrogenation-induced increase in the formation of 18:2 from 18:1-CoA (proceeding partly through direct desaturation of PC) may be due to changes in conformation of the membrane-bound desaturase enzyme complex as a result of controlled rigidification of the surrounding lipids. The operation of such a self-regulating control mechanism would be consistent with a previously proposed model for microsomal desaturase action.     

Effect of retinoic acid on the acylation of phospholipids in granulocytes in vitro

The influence of retinoic acid on the incorporation of [1-14C]palmitic acid and [1-14C]arachidonic acid into phospholipids was examined in guinea pig peritoneal granulocytes. All-trans-retinoic acid inhibited the incorporation of both fatty acids into phosphatidic acid and phosphatidylinositol. However, it stimulated the incorporation of both fatty acids into phosphatidylcholine but not other phospholipids. All-trans-retinoic acid was more effective than 13-cis-retinoic acid. The influence of all-trans-retinoic acid on the acylation of phospholipids was concentration-dependent with significant effect occurring at 2.1 microM. The loss of labeled fatty acids from prelabeled phospholipids and the transport of labeled fatty acids into granulocytes were not responsive to the presence of retinoic acid in the incubation media. These results suggest that retinoic acid may affect the activities of acyltransferases involved in the synthesis of phosphatidic acid, phosphatidylinositol and phosphatidylcholine.     

Lipid profiles of Aspergillus niger and its unsaturated fatty acid auxotroph, UFA2

A comparative study of the mycelial lipid composition of a wild strain (V35) and one unsaturated fatty acid auxotroph (UFA2) of Aspergillus niger has been performed. The lipid composition of both strains are qualitatively the same but quantitatively different. All the strains contain the following phospholipids: cardiolipin, phosphatidylethanolamine, phosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylcholine, and phosphatidylserine; and triglycerides, diglycerides, monoglycerides, ergosterol, and sterol esters as the neutral lipids; mono- and di-galactosyl diglyceride as the major glycolipids along with small amounts of the corresponding mannose analogs. Phosphatidylethanolamine and phosphatidylcholine constitute the bulk of the phospholipids. The mutant (UFA2) contains a higher level of glycerides and lower levels of sterol (both free and esterified form), phospholipids, and glycolipids than the wild type. Aspergillus niger contains C16 to C18 saturated and unsaturated fatty acids. Small amounts of long-chain (C20 to C24) and short-chain (C10 to C14) saturated and unsaturated acids are also present. Linoleic, oleic, and palmitic are the major acids, stearic and linolenic acids being minor ones. UFA2 grows only in the presence of unsaturated fatty acid (C16 or C18) and accumulates a higher concentration of supplemented acid which influences its fatty acid profile.     

Influence of temperature on complement-dependent immune damage to liposomes

Maximal release of trapped liposomal glucose, in the presence of saturating amounts of liposomal antigen (galactocerebroside), antiserum (anti-galactocerebroside), and complement, was dependent on temperature. At lower temperatures (20--25 degrees C), maximal glucose release was inversely related to liposomal phospholipid fatty acyl chain length (dimyristoyl phosphatidylcholine > dipalmitoyl phosphatidylcholine > distearoyl phosphatidylcholine > sphingomyelin). At higher temperatures (32--35 degrees C) a limiting plateau of glucose release, at approx. 60%, was reached, or approached, by all preparations. Sphingomyelin liposomes still released less glucose than those prepared from other phospholipids, even at 35 degrees C. The titers of antiserum and complement (ABL50/ml and CL50/ml) were dependent on temperature, and differences based on liposomal phospholipid fatty acyl chain length were observed. Analysis of antiserum and complement-dependence on temperature, and on phospholipid type, revealed that although antibody binding to galactocerebroside undoubtedly was subject to steric hindrance due to interference by surrounding phospholipids at 20--25 degrees C, steric hindrance did not play a major role in blocking antibody binding above 32 degrees C.