Intramembraneous hydrogenation of mitochondrial lipids reduces the substrate availability, but not the enzyme activity of endogenous phospholipase A. The role of polyunsaturated phospholipid species

Cyanobacterial monogalactosyldiacylglycerol-synthesis pathway is involved in normal unsaturation of galactolipids and low-temperature adaptation of Synechocystis sp. PCC 6803

We characterized certain physiological functions of cyanobacterial monoglucosyldiacylglycerol using a Synechocystis sp. PCC 6803 mutant in which the gene for monoglucosyldiacylglycerol synthase had been disrupted and its function complemented by inclusion of an Arabidopsis monogalactosyldiacylglycerol synthase gene. By using this method, we prepared the first viable monoglucosyldiacylglycerol-deficient mutant of cyanobacterium and found that monoglucosyldiacylglycerol is not essential for its growth and photosynthesis under a set of "normal growth conditions" when monogalactosyldiacylglycerol is adequately supplied by the Arabidopsis monogalactosyldiacylglycerol synthase. The mutant had healthy thylakoid membranes and normal pigment content. The membrane lipid composition of the mutant was similar with that of WT except lack of monoglucosyldiacylglycerol and a slight increase in the level of phosphatidylglycerol at both normal and low temperatures. However, the ratio of unsaturated fatty acids in monogalactosyldiacylglycerol and digalactosyldiacylglycerol was reduced in the mutant compared with WT. Although the growth of the mutant was indistinguishable with that of WT at normal growth temperature, it was markedly retarded at low temperature compared with that of WT. Our data indicated the possibility that cyanobacterial monogalactosyldiacylglycerol-synthesis pathway might be required for the adequate unsaturation level of fatty acids in galactolipids and affect the low-temperature sensitivity.

Catalytic hydrogenation of polyunsaturated biological membranes: effects on membrane fatty acid composition and physical properties

The relationship between phospholipid saturation and membrane physical structure in a complex, highly polyunsaturated biological membrane (trout liver microsomes) has been studied by the graded and specific hydrogenation of polyunsaturated fatty acids. The homogeneous catalyst Pd(QS)2 caused rapid and effective hydrogenation, increasing the proportion of saturated fatty acids from 20-30% up to 60%, without loss or fragmentation. Long chain, polyunsaturated fatty acids (20:5 omega 3, 22:6 omega 3) were rapidly converted to a large number of partially hydrogenated isomers, and ultimately to the fully saturated C20 or C22 fatty acids. C18 mono- and di-unsaturates showed slower rates of hydrogenation. Increased saturation was closely associated with an increased membrane physical order as determined by the fluorescence anisotropy probe, 1,6-diphenyl-1,3,5-hexatriene. However, extensive hydrogenation led to highly ordered membranes exhibiting a gel-liquid crystalline phase transition between 30 and 60 degrees C. Polyunsaturated membranes can thus be converted into partially or substantially saturated membranes with measurable phase structure without direct alteration of other membrane components. This offers a less equivocal means of assessing the influence of polyunsaturation upon membrane structure and function.

Modulation of lipid unsaturation and membrane fluid state in mammalian cells by stable transformation with the delta9-desaturase gene of Saccharomyces cerevisiae

The composition and physical state of membrane lipids determine the dynamic nature of membranes, which in turn, could directly be linked to the activity of various membrane-associated cellular functions. To better understand the molecular basis of different membrane-related phenomena we established a novel strategy to alter unsaturation of mammalian cell membranes with an identical genetic background. We transfected L929 mouse fibroblastoid cells with DNA constructs containing the Delta9-fatty acid desaturase gene (Ole1) of S. cerevisiae under the control of desaturase promoters derived either from wild type or mutant strains of the dimorphic fungus H. capsulatum.

Evidence for a lipochaperonin: association of active protein-folding GroESL oligomers with lipids can stabilize membranes under heat shock conditions

During heat shock, structural changes in proteins and membranes may lead to cell death. While GroE and other chaperone proteins are involved in the prevention of stress-induced protein aggregation and in the recovery of protein structures, a mechanism for short-term membrane stabilization during stress remains to be established. We found that GroEL chaperonin can associate with model lipid membranes. Binding was apparently governed by the composition and the physical state of the host bilayer. Limited proteolysis of GroEL oligomers by proteinase K, which removes selectively the conserved glycine- and methionine-rich C terminus, leaving the chaperonin oligomer intact, prevented chaperonin association with lipid membranes. GroEL increased the lipid order in the liquid crystalline state, yet remained functional as a protein-folding chaperonin. This suggests that, during stress, chaperonins can assume the functions of assisting the folding of both soluble and membrane-associated proteins while concomitantly stabilizing lipid membranes.

Dietary lipid and iron modify normal colonic mucosa without affecting phospholipase A2 activity

Phospholipase A2 (PLA2) functions as the rate-limiting step in arachidonic acid metabolism and in the removal of damaged or peroxidized membrane lipids. It is elevated in some human tumors and may be involved with mechanisms of tumor promotion. In vitro systems have shown PLA2 activity to be altered by variations in fatty acid and antioxidant components. This study encompassed two objectives. First, PLA2, activity in colon tumors produced using azoxymethane (AOM) in Fischer-344 rats was examined. Secondly, this study tested the effect of iron supplementation as a potential pro-oxidant in diets of varied fatty acid composition on PLA2 activity. Diets included 35 or 140 mg/kg or iron in AIN-76A based diets high in corn oil, menhaden oil, or beef tallow. Results for the first objective showed PLA2 activity to be significantly higher in colon tumors than in normal mucosa with the increase due primarily to an increase in activity within a particulate subcellular fraction. In the second objective, fatty acid composition of colon mucosa was altered by both dietary fat and iron. Animals fed beef tallow had the highest level of oleic acid and corn oil-fed animals had the highest level of linoleic acid. Animals fed menhaden oil had the lowest level of arachidonic acid and highest level of alpha-linolenic, eicosapentaenoic, docosapentaenoic, and docosahexaenoic acids. Iron supplementation in diets high in corn oil resulted in decreased membrane composition of palmitoleic and delta-linolenic acid. In spite of these changes in membrane composition, there were no changes in PLA2 activity. These results show that PLA2 activity is increased in AOM-induced tumors but that diet alone does not influence PLA2 activity in this model.

Phospholipase A2 activity in vitro cultured cells--influence of ascorbate supplementation

Non-malignant LLCMK cells and malignant B16 cells were supplemented with ascorbate, over the concentration range 0-100 micrograms/ml ascorbate. The effects of ascorbate supplementation on cell growth and phospholipase A2 activity of the membrane fractions of the respective cell lines were determined. Increasing ascorbate supplementation had a significant inhibitory effect on the growth of the B16 cells. Phospholipase A2 activity in the control B16 cells was lower than that detected in the control LLCMK cells. Phospholipase A2 activity decreased significantly in the B16 cells upon increasing ascorbate supplementation, while the supplementation of ascorbate to the LLCMK cells did not have any significant effect on phospholipase A2 activity in these cells.

Effects of various dietary fats on cardiolipin acyl composition during ontogeny of mice

Cardiolipin (CL) is a unique mitochondrial phospholipid, containing up to 85 wt% 18:2n-6 in mammals. The influence of maternal dietary fatty acids on the acyl composition of offspring CL has not been examined previously. Adult female mice were thus fed diets rich in 18:1n-9 (olive oil), 18:2n-6 (safflower oil), 18:3n-3 (linseed oil) or 20:5n-3 and 22:6n-3 (fish oil/safflower, 9:1, w/w), for a five month period, encompassing two breeding cycles. Offspring from the second breeding cycle were then fed these diets. The acyl composition of CL, phosphatidylcholine and phosphatidylethanolamine from liver and heart was evaluated from mice killed 3, 18 and 42 days after parturition. The primary nutrient sources at these three time points were transplacental nutrients, breast milk and the diet, respectively. Maternal diet was found to influence the acyl composition of CL via both placental transfer of fatty acids and breast milk. Fish oil feeding resulted in replacement of a substantial portion of 18:2n-6 with 22:6n-3; after 42 days, the area% of 18:2n-6 in heart CL was reduced from 62% in safflower oil fed mice to 12%. In comparison to fish oil feeding, linseed oil feeding resulted in a much lower accumulation of 22:6n-3. Olive oil feeding resulted in substantial replacement of 18:2n-6 with 18:1n-9 (18:2n-6 was reduced from 62% to 31%). Physiologically, these findings are relevant because changes in CL acyl composition may influence the activity of associated inner mitochondrial membrane enzymes.

Effect of an essential fatty acid deficiency on the phospholipid composition in anterior pituitary membranes

The effects of an essential fatty acid deficient diet were investigated on the phospholipid fatty acids of several membrane fractions of the rat anterior pituitary, the secretion of which is known to be partly dependent on the membrane phospholipidic constituents. In standard dietary conditions, arachidonic acid (20:4n-6) and its elongation product, adrenic acid (22:4n-6), were the two main polyunsaturated fatty acids in all fractions studied. In rats deprived of EFA for 6 weeks after weaning, the levels of both 20:4n-6 and 22:4n-6 were not changed in microsomal + plasma membrane and nuclear fractions, whereas they were decreased in heavy mitochondrial and light mitochondrial fractions. The present data suggest a mechanism of compensation between membrane fractions which may preferentially preserve 20:4n-6 and 22:4n-6 in discrete membrane fractions.

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Replacement of vertebrate serum with lipids and other factors in the culture of invertebrate cells, tissues, parasites, and pathogens

Culture medium supplementation with vertebrate serum results in the selection of fibroblastoid insect cell lines and a general decline during continuous subculturing of both morphologic and functional differentiation of the surviving cells. Essential lipid mixtures can substitute for vertebrate serum in the culture of insect and some vertebrate cells, tissues, parasites, and pathogens. The provision of sterols and essential (with nonessential) polyunsaturated fatty acids as phospholipids in oxidation-protected peptoliposomes or proteoliposomes allows cells in culture to duplicate in vivo specific membranes more accurately. Such lipid-corrected membranes allow cultured cells to communicate with neighboring cells through the extracellular matrix, effectively transmit hormonal signals directly and via receptor control, and respond with various tissue-specific functions and differentiation states as directed.

Complex hydrogenation/oxidation reactions of the water-soluble hydrogenation catalyst palladium di (sodium alizarinmonosulfonate) and details of homogeneous hydrogenation of lipids in isolated biomembranes and living cells

Palladium di (sodium alizarinmonosulfonate) is a highly efficient catalyst for the hydrogenation of unsaturated fatty acids esterified in lipids of model or biological membranes, enabling the study of the relationship between function and the physical state of membranes. However, the catalyst shows a complex behavior in the action of molecular hydrogen and oxygen, giving rise to the formation of at least four products. Two of these are free radicals. Owing to this complexity, precise control of the reaction requires pretreatment of the catalyst. When partial hydrogenation of the palladium complex is followed by air oxidation, a catalyst solution is produced which is stable on air and maintains catalytic hydrogenation activity for several days. This form of the catalyst induces hydrogenation of unsaturated lipids with no induction period making a strict timing of the procedure possible. Of the several other factors affecting the outcome of membrane hydrogenations, one of the most important is the accessibility to the catalyst of particular membrane regions or lipid pools. Differences in accessibility may arise as a consequence of different local microviscosities or their change during hydrogenation, of the appearance of distinct liquid crystalline phases, and of strong protein-lipid interactions. Obviously, in case of whole-cell hydrogenations, the accessibility is influenced by the spatial separation of the organelles, as well.