Fatty Acids In Yeast Research Articles

Adaptation to oxidative stress induced by polyunsaturated fatty acids in yeast

To create a conditional system for molecular analysis of effects of polyunsaturated fatty acids (PUFA) on cellular physiology, we have constructed a strain of yeast ( Saccharomyces cerevisiae) that functionally expresses, under defined conditions, the Δ12 desaturase gene from the tropical rubber tree, Hevea brasiliensis. This strain produces up to 15% PUFA, exclusively under inducing conditions resulting in production of 4-hydroxy-2-nonenal, one of the major end products of n − 6 polyunsaturated fatty acid peroxidation. The PUFA-producing yeast was initially more sensitive to oxidative stress than the wild-type strain. However, over extended time of cultivation it became more resistant to hydrogen peroxide indicating adaptation to endogenous oxidative stress caused by the presence of PUFA. Indeed, PUFA-producing strain showed an increased concentration of endogenous ROS, while initially increased hydrogen peroxide sensitivity was followed by an increase in catalase activity and adaptation to oxidative stress. The deletion mutants constructed to be defective in the catalase activity lost the ability to adapt to oxidative stress. These data demonstrate that the cellular synthesis of PUFA induces endogenous oxidative stress which is overcome by cellular adaptation based on the catalase activity.

Metabolism of fatty acid in yeast: addition of reducing agents to the reaction medium influences β-oxidation activities, γ-decalactone production, and cell ultrastructure inSporidiobolus ruineniicultivated on ricinoleic acid methyl ester

The sensitivity of Sporidiobolus ruinenii yeast to the use of reducing agents, reflected in changes in the oxidoreduction potential at pH 7 (Eh7) environment, ricinoleic acid methyl ester catabolism, gamma-decalactone synthesis, cofactor level, beta-oxidation activity, and ultrastructure of the cell, was studied. Three environmental conditions (corresponding to oxidative, neutral, and reducing conditions) were fixed with the use of air or air and reducing agents (hydrogen and dithiothreitol). Lowering Eh7 to neutral conditions (Eh7 = +30 mV and +2.5 mV) favoured the production of lactone more than the more oxidative condition (Eh7 = +350 mV). In contrast, when a reducing condition was used (Eh7 = -130 mV), the production of gamma-decalactone was very low. These results were linked to changes in the cofactor ratio during lactone production, to the beta-oxidation activity involved in decanolide synthesis, and to ultrastructural modification of the cell.

Beta oxidation of oleic acid in yeast requires a thioesterase but not dienoyl‐CoA isomerase

The β-oxidation of unsaturated fatty acids in yeast was studied by measuring and comparing the growth of wild-type S. cerevisiae with the growth of mutants that either have a deleted Δ3,5, Δ2,4-dienoyl-CoA isomerase (dienoyl-CoA isomerase) gene (DCI1) or thioesterase gene (TES1) on oleic or palmitic acid. Growth of wild-type and dci1 strains on oleic acid was indistinguishable, whereas the tes1 mutant grew slower and to a lower density. In contrast, all three strains grew in a similar manner on palmitic acid. 3,5-Tetradecanoic acid was detected in the medium by gas chromatography/mass spectrometry after growth of wild-type cells on oleic acid but not when palmitic acid was the carbon source. When the tes1 mutant was transformed with a plasmid expressing human dienoyl-CoA isomerase, the growth defect on oleic acid was partially corrected. These observations support the conclusion that the product of the DCI1 gene does not function as dienoyl-CoA isomerase in oleate β-oxidation. Hence 3,5-tetradecadienoyl-CoA, an intermediate of oleate β-oxidation, does not seem to be degraded via the reductase-dependent pathway but rather by an alternate pathway that involves a thioesterase, which hydrolyzes 3,5-tetradecadienoyl-CoA to 3,5-tetradecadienoic acid that is excreted into the growth medium. (Supported by NIH Grants GM08168 and RR03060 and Grant 0350364N from the American Heart Association).

Production of (10 E,12 Z)-conjugated linoleic acid in yeast and tobacco seeds

The polyenoic fatty acid isomerase from Propioniumbacterium acnes (PAI) was expressed in E. coli and biochemically characterized. PAI catalyzes the isomerization of a methylene-interrupted double bond system to a conjugated double bond system, creating (10 E,12 Z)-conjugated linoleic acid (CLA). PAI accepted a wide range of free polyunsaturated fatty acids as substrates ranging from 18:2 fatty acids to 22:6, converting them to fatty acids with two or three conjugated double bonds. For expression of PAI in yeast the PAI-sequence encoding 20 N-terminal amino acid residues was altered for optimal codon usage, yielding codon optimized PAI ( coPAI). The percentage of 10,12-CLA of total esterified fatty acids was 8 times higher in yeast transformed with coPAI than in cells transformed with PAI. CLA was detected in amounts up to 5.7% of total free fatty acids in yeast transformed with coPAI but none was detected in yeast transformed with PAI. PAI or coPAI under the control of the constitutive CaMV 35S promoter or the seed-specific USP promoter was transformed into tobacco plants. CLA was only detected in seeds in coPAI-transgenic plants. The amount of CLA detected in esterified fatty acids was up to 0.3%, in free fatty acids up to 15%.

Metabolism of fatty acid in yeast: Characterisation of β-oxidation and ultrastructural changes in the genus Sporidiobolus sp. cultivated on ricinoleic acid methyl ester

Cell structure modifications and β-oxidation induction were monitored in two strains of Sporidiobolus, Sp. Ruinenii and Sp. pararoseus after cultivation on ricinoleic acid methyl ester. Ultrastructural observations of the yeast before and after cultivation on fatty acid esters did not reveal major modifications in Sp. ruinenii. Unexpectedly, in Sp. pararoseus a proliferation of the mitochondrion was observed. After induction, Sp. ruinenii principally exhibited an increase in the activities of acyl-CoA oxidase (ACO), hydroxyacyl-CoA deshydrogenase (HAD), thiolase and catalase. In contrast, Sp. pararoseus lacked ACO and catalase activities, but an increase in acyl-CoA deshydrogenase (ACDH) and enoyl-CoA hydratase (ECH) activity was observed. These data suggest that in Sp. ruinenii, β-oxidation is preferentially localized in the microbody, whereas in Sp. pararoseus it might be localized in the mitochondria.

Apparent Digestibility Coefficients of Various Feed Ingredients for Grouper Epinephelus coioides

Apparent digestibility coefficients (ADC) of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in white fish meal, brown fish meal, soybean meal, peanut meal, and yeast were determined for grouper Epinephelus coioides. Apparent digestibility was determined using a reference diet with 0.5% chromic oxide indicator and test diets that contained 70% reference diet and 30% of the feed ingredient being evaluated. The fish, averaging 12.0 g, were held in 250-L tanks at a density of 30 fish per tank. Feces were collected from three replicate groups-of fish. Apparent dry matter digestibility of ingredients was 78.85 ± 2.43, 79.11 ± 0.61, 69.85 ± 3.60, 73.67 ± 2.30 and 57.70 ± 4.69% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent gross energy digestibility of ingredients was 93.27 ± 2.90, 89.48 ± 1.78, 70.52 ± 4.01, 73.13 ± 2.41 and 51.67 ± 2.01% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent protein digestibility of ingredients was 89.82 ± 1.24, 87.34 ± 1.25, 83.97 ± 1.92, 80.79 ± 1.95, and 61.14 ± 0.54% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. White fish meal and brown fish meal showed higher protein digestibility among ingredients tested (P ± 0.01). Lipid digestibility of ingredients was high (90.66-94.48%) and not significantly different except for yeast. Amino acid availability values for test ingredients were similar to values of protein digestibility. Amino acid availability values of white fish meal and brown fish meal were higher than other ingredients. Fatty acid availability values for test ingredients were similar to values of lipid digestibility. In general, the digestibility of most fatty acids was over 80% in all ingredients, except for 14:0 in yeast and 18:0 in peanut meal, PUFA + HUFA > MUFA > SFA. Longer-chain saturated fatty acids were less digestibility, except for 14:0, with digestibilities diminishing as fatty acid chain length increased. Apparent digestibility of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in yeast was the lowest among the ingredients.

Upstream of Growth and Differentiation Factor 1 (uog1), a Mammalian Homolog of the Yeast Longevity Assurance Gene 1 (LAG1), RegulatesN-Stearoyl-sphinganine (C18-(Dihydro)ceramide) Synthesis in a Fumonisin B1-independent Manner in Mammalian Cells

The longevity assurance gene (LAG1) and its homolog (LAC1) are required for acyl-CoA-dependent synthesis of ceramides containing very long acyl chain (e.g. C26) fatty acids in yeast, and a homolog of LAG1, ASC1, confers resistance in plants to fumonisin B(1), an inhibitor of ceramide synthesis. To understand further the mechanism of regulation of ceramide synthesis, we now characterize a mammalian homolog of LAG1, upstream of growth and differentiation factor-1 (uog1). cDNA clones of uog1 were obtained from expression sequence-tagged clones and sub-cloned into a mammalian expression vector. Transient transfection of human embryonic kidney 293T cells with uog1 followed by metabolic labeling with [4,5-(3)H]sphinganine or L-3-[(3)H]serine demonstrated that uog1 conferred fumonisin B(1) resistance with respect to the ability of the cells to continue to produce ceramide. Surprisingly, this ceramide was channeled into neutral glycosphingolipids but not into gangliosides. Electrospray tandem mass spectrometry confirmed the elevation in sphingolipids and revealed that the ceramides and neutral glycosphingolipids of uog1-transfected cells contain primarily stearic acid (C18), that this enrichment was further increased by FB(1), and that the amount of stearic acid in sphingomyelin was also increased. UOG1 was localized to the endoplasmic reticulum, demonstrating that the fatty acid selectivity and the fumonisin B(1) resistance are not due to a subcellular localization different from that found previously for ceramide synthase activity. Furthermore, in vitro assays of uog1-transfected cells demonstrated elevated ceramide synthase activity when stearoyl-CoA but not palmitoyl-CoA was used as substrate. We propose a role for UOG1 in regulating C18-ceramide (N-stearoyl-sphinganine) synthesis, and we note that not only is this the first case of ceramide formation in mammalian cells with such a high degree of fatty acid specificity, but also that the N-stearoyl-sphinganine produced by UOG1 most significantly impacts neutral glycosphingolipid synthesis.

The Acyl-CoA Synthetases Encoded within FAA1 andFAA4 in Saccharomyces cerevisiaeFunction as Components of the Fatty Acid Transport System Linking Import, Activation, and Intracellular Utilization

Exogenous long-chain fatty acids are activated to coenzyme A derivatives prior to metabolic utilization. In the yeast Saccharomyces cerevisiae, the activation of these compounds prior to metabolic utilization proceeds through the fatty acyl-CoA synthetases Faa1p and Faa4p. Faa1p or Faa4p are essential for long-chain fatty acid import, suggesting that one or both of these enzymes are components of the fatty acid transport system, which also includes Fat1p. By monitoring the intracellular accumulation of the fluorescent long-chain fatty acid analogue 4,4-difluoro-5-methyl-4-bora-3a,4a-diaza-s-indacene-3-dodecanoic acid, long-chain fatty acid transport was shown to be severely restricted in a faa1 Delta faa4 Delta strain. These data established for the first time a mechanistic linkage between the import and activation of exogenous fatty acids in yeast. To investigate this linkage further, oleoyl CoA levels were defined following incubation of wild type and mutant cells with limiting concentrations of exogenous oleate. These studies demonstrated oleoyl CoA levels were reduced to less than 10% wild-type levels in faa1 Delta and faa1 Delta faa4 Delta strains. Defects in metabolic utilization and intracellular trafficking were also found in the fatty acyl-CoA synthetase-deficient strains. The faa1 Delta faa4 Delta strain had a marked reduction in endogenous acyl-CoA pools, suggesting these enzymes play a role in maintenance of endogenous acyl-CoA pools, metabolism and trafficking. In addition, this strain had levels of in vivo beta-oxidation of exogenous oleate reduced 3-fold when compared with the isogenic parent. Northern analyses demonstrated an additional defect in fatty acid trafficking as FAA1 or FAA4 were required for the transcriptional regulation of the genes encoding the peroxisomal enzymes acyl-CoA oxidase (POX1) and medium-chain acyl-CoA synthetase (FAA2). These data support the hypothesis that fatty acyl-CoA synthetase (Faa1p or Faa4p) functions as a component of the fatty acid import system by linking import and activation of exogenous fatty acids to intracellular utilization and signaling.

The genetics of fatty acid metabolism in Saccharomyces cerevisiae.

Long-chain fatty acids are a vital metabolic energy source and are building blocks of membrane lipids. The yeast Saccharomyces cerevisiae is a valuable model system for elucidation of gene-function relationships in such eukaryotic processes as fatty acid metabolism. Yeast degrades fatty acids only in the peroxisome, and recently, genes encoding core and auxiliary enzymes of peroxisomal beta-oxidation have been identified. Mechanisms involved in fatty acid induction of gene expression have been described, and novel fatty acid-responsive genes have been discovered via yeast genome analysis. In addition, a number of genes essential for synthesis of the variety of fatty acids in yeast have been cloned. Advances in understanding such processes in S. cerevisiae will provide helpful insights to functional genomics approaches in more complex organisms.

Cloning of delta12- and delta6-desaturases from Mortierella alpina and recombinant production of gamma-linolenic acid in Saccharomyces cerevisiae.

Two cDNA clones with homology to known desaturase genes were isolated from the fungus Mortierella alpina. The open reading frame in one clone encoded 399 amino acids and exhibited delta12-desaturase activity when expressed in Saccharomyces cerevisiae in the presence of endogenous fatty acid substrate oleic acid. The insert in another clone contained an open reading frame encoding 457 amino acids and exhibited delta6-desaturase activity in S. cerevisiae in the presence of exogenous fatty acid substrate linoleic acid. Expression of the delta12-desaturase gene under appropriate media and temperature conditions led to the production of linoleic acid at levels up to 25% of the total fatty acids in yeast. When linoleic acid was provided as an exogenous substrate to the yeast cultures expressing the delta6-desaturase activity, the level of gamma-linolenic acid reached 10% of the total yeast fatty acids. Co-expression of both the delta6- and delta12-desaturase cDNA resulted in the endogenous production of gamma-linolenic acid. The yields of gamma-linolenic acid reached as high as 8% of total fatty acids in yeast.

Purification, Identification, and Properties of a Saccharomyces cerevisiae Oleate-activated Upstream Activating Sequence-binding Protein That Is Involved in the Activation of POX1

Peroxisomes have a central function in lipid metabolism, and it is well established that these organelles are inducible by many compounds including fatty acids. Peroxisomes are the sole site for the beta-oxidation of fatty acids in yeast. The first and rate-limiting enzyme of this cycle is fatty acyl-CoA oxidase. The gene encoding this enzyme in Saccharomyces cerevisiae (POX1) undergoes a complex regulation that is dependent on the growth environment. When this yeast is grown in medium containing oleic acid as the main carbon source, peroxisomes are induced and POX1 expression is activated. When cells are grown in the presence of glucose, the expression of POX1 mRNA is repressed, whereas growth on a carbon source such as glycerol or raffinose causes derepression. This rigorous regulation is brought about by the complex interactions between trans-acting factors and cis-elements in the POX1 promoter. Previously, we characterized regulatory elements in the promoter region of POX1 that are involved in the repression and activation of this gene (Wang, T., Luo, Y., and Small, G. M. (1994) J. Biol. Chem. 269, 24480-24485). In this study we have purified and identified an oleate-activated transcription factor (Oaf1p) that binds to the activating sequence (UAS1) in the POX1 gene. The protein has a predicted molecular mass of approximately 118 kDa.

A Novel Cytochrome b5-like Domain Is Linked to the Carboxyl Terminus of the Saccharomyces cerevisiae Δ-9 Fatty Acid Desaturase

Cytochrome b5 is an amphipathic mobile membrane protein that is predominantly located at the endoplasmic reticulum surface. It is an essential component of a number of membrane-bound redox systems. In animal and fungal cells cytochrome b5 is thought to be an electron donor for sterol modifying enzymes and fatty acid desaturases. Disruption of the Saccharomyces cytochrome b5 gene, however, yielded cells that had no nutritional requirement for either sterols or unsaturated fatty acids. Expression of sterol and fatty acid-modifying genes was increased in the cytochrome b5-disrupted cells, however, suggesting that cytochrome b5 may play some nonessential role in these functions. Unsaturated fatty acids in yeast are formed by Ole1p, an oxygen-dependent delta-9 fatty acid desaturase that is an intrinsic endoplasmic reticulum membrane protein. Although the yeast delta-9 fatty acid desaturase does not appear to require cytochrome b5, introduction of the rat liver stearoyl-CoA desaturase gene into an ole1-disrupted, cytochrome b5-disrupted yeast strain revealed that this enzyme specifically requires cytochrome b5 to function. Comparison of the coding sequences of the yeast and rat desaturase genes showed that the yeast protein contains a 113-amino acid carboxyl-terminal extension not found in the rat enzyme. That extension has regions of strong homology to cytochrome b5, particularly in the heme binding and electron transfer motifs. Truncation or disruption of the desaturase cytochrome b5-like domain in cells that contain the wild type diffusible b5 produced unsaturated fatty acid auxotrophy, suggesting that the cytochrome b5-like domain of Ole1p plays an essential role in the desaturase reaction.

Determination of Selected Sterols and Fatty Acids in Yeast

The level of lipids in yeast cells is known to be an important indicator of the yeast's vitality and expected fermentative performance. Measurement of the concentration of these lipids provides a useful tool for studying and managing yeast performance during fermentation. A method is developed for the quantitative determination of selected lipids in brewers' yeast. It consists of the optimized hydrolysis and extraction of the most important sterols and long chain fatty acids from the yeast in a single sample preparation procedure followed by their accurate individual quantitation by chromatographic techniques. Highpressure liquid chromatography with multiple wavelength diode-array detection is used for the simultaneous detection of sterols (ergosterol and lanosterol) and a sterol precursor (squalene). The reproducibility error for all measured sterols is less than 9% over the concentration range 0.1-1% (measurement based on dry cell weight). The C 16 and C 18 saturated and monounsaturated fatty acids are quantitated in their free (underivatized) form by gas chromatography. The reproducibility error for all the measured fatty acids is less than 6% over the concentration range 0.5-2.5% (measurement based on dry cell weight).

Use of an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae to modify the lipid composition and function of mitochondrial membranes.

KD115 (ol1), an unsaturated fatty acid auxotroph of S. cerevisiae, was grown in a semi-synthetic medium supplemented with 3.3 x 10(-4) M palmitoleic (cis 16:1) or palmitelaidic (trans 16:1) acids. The parent strain S288C was studied as a control. The lipid composition (fatty acids, neutral lipids, and phospholipids), respiratory activity (O2 consumption), and ultrastructure were compared in mutant yeast grown with each unsaturated fatty acid supplement. The fatty acid supplement represented 70-80% of the yeast fatty acids. Yeast grown in trans 16:1 contained more squalene, a higher ratio of phosphatidylethanolamine (PE) to phosphatidylcholine (PC), and had 10-20% of the respiratory activity compared to the same yeast grown in cis 16:1. The mitochondrial morphology of yeast in each growth supplement was notably different. The use of mixtures of cis and trans 16:1 in different proportions revealed that the PE/PC ratio, the squalene content, the respiratory defect, and the mitochondrial morphology were all similarly dependent on the fraction of trans 16:1 in the mixtures. As little as 10-20% of cis 16:1 in the mixture was sufficient to abrogate the physiological effects of trans 16:1 on each of the parameters noted above. The combined effects of high content of trans unsaturated fatty acid and the altered phospholipid composition seem to account for the decrease in lipid fluidity, the defective structure and function of the mitochondrial membrane.

Differentiation of yeast species, and strains within a species, by cellular fatty acid analysis. 1. Application of an adapted technique to differentiate between strains of Saccharomyces cerevisiae

A fatty acid analysis technique was adapted to give colourless, moisture-free, completely esterified fatty acid extracts from yeasts. Capillary columns with different stationary phases spanning a range of polarity were used ensure optimal resolution of the yeast fatty acids. 15 fatty acids were identified in 13 strains of Saccharomyces cerevisiae by comparison of relative retention times, methyl ester mass spectra and picolinyl ester mass spectra with those of reference standards. Fatty acids were identified by interpretation of picolinyl ester mass spectra in the absence of suitable reference standards. The various strains showed district variations in the mean relative percentages of the fatty acids present in the cellular material. These variations were strain-specific and the fatty acid profiles could be satisfactorily reproduced. Percentage deviation for 10 fatty acids, C14: 0, C14: 1(9), C15: 0, C15: 1(9), C16: 1(11), C18: 0, C18: 1(9) and C18: 1(11) was good and the variation in the mean relative percentages of these fatty acids between strains afforded unambiguous strain differentiation after subjecting the data to an ANOVA. Minor fatty acids (relative percentages ⩽ 1%) were important contributors to the differentiating ability of the technique.

Superoxide dismutase deficiency and the toxicity of the products of autooxidation of polyunsaturated fatty acids in yeast

Mutants of Saccharomyces cerevisiae, deficient in cytosolic superoxide dismutase and catalase activities were used to study the role of various oxygen species in the process of lipid peroxidation in yeast cells. Lipid peroxidation does not occur normally in yeast, because this organism is unable to form fatty acids with more than one double bond, whereas under physiological conditions, only fatty acids with at least two double bonds undergo this process. The fatty acid content of cellular lipids was modified by growing the cells in anoxia in the presence of oleic or linolenic acid. Toxic effects of oxygen were observed almost exclusively in those cells of yeast mutants deficient in superoxide dismutase, which contain linolenic acid in cellular lipids. Hypersensitivity of the mutant cells, however, results mainly from toxic effects of the products of autooxidation of extracellular fatty acids. These facts suggest that superoxide dismutases are in some way involved in preventing toxic effects of the products of lipid peroxidation and to some extent prevent the process of lipid peroxidation.

Fatty Acid Profiles of Some Cultured and Wild Yeasts in Brewery

A simple, rapid, microscale, gas chromatographic method was developed for the determination of fatty acids in yeast. The method includes a simplified procedure for extraction and saponification, the use of a direct pyrolytic methylation technique, and the use of a high resolution wall-coated open tubular column. A total of 19 strains of cultured, wild, and alcohol-tolerant yeasts previously grown in brewer's wort at 20°C were analyzed. Chromatographic and quantitative profiles for each strain of yeast were established. Apart from some subtle differences among the yeasts, three major distinctions were apparent: 1) Cultured yeasts contained more saturated fatty acids, among which palmitic acid was the most abundant. On the other hand, wild and alcohol-tolerant yeasts contained more unsaturated fatty acids, among which palmitoleic acid was usually the most abundant. 2) The ratio of stearic to oleic acid was greater than 1 for cultured yeasts but smaller than 1 for the other yeasts. 3) Some additional fatty acids hitherto unidentified were present in most of the wild and alcohol-tolerant yeasts. Differentiating or identifying brewery yeasts by analyzing their fatty acid composition would therefore appear possible.

Fatty Acid Profiles of Some Cultured and Wild Yeasts in Brewery

A simple, rapid, microscale, gas chromatographic method was developed for the determination of fatty acids in yeast. The method includes a simplified procedure for extraction and saponification, the use of a direct pyrolytic methylation technique, and the use of a high resolution wall-coated open tubular column. A total of 19 strains of cultured, wild, and alcohol-tolerant yeasts previously grown in brewer's wort at 20°C were analyzed. Chromatographic and quantitative profiles for each strain of yeast were established. Apart from some subtle differences among the yeasts, three major distinctions were apparent: 1) Cultured yeasts contained more saturated fatty acids, among which palmitic acid was the most abundant. On the other hand, wild and alcohol-tolerant yeasts contained more unsaturated fatty acids, among which palmitoleic acid was usually the most abundant. 2) The ratio of stearic to oleic acid was greater than 1 for cultured yeasts but smaller than 1 for the other yeasts. 3) Some additional fatty acids hitherto unidentified were present in most of the wild and alcohol-tolerant yeasts. Differentiating or identifying brewery yeasts by analyzing their fatty acid composition would therefore appear possible.

Changes in stereospecific distribution of yeast fatty acids with age

Stereospecific analyses of glycerolipids from 7-, 14- and 21-day-old cultures of the yeast Lipomyces lipoferus revealed that each position of the glycerolipids had a unique distribution of fatty acids which changed to varying degrees with age, and that, in the triacylglycerols, age had a greater effect on fatty acid content at sn-3 that at sn-1 or sn-2. Age-related changes in unsaturation were, however, greater in the phospholipids than in the triacylglycerols. Among the major phospholipids of L. lipoferus (phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine), changes in the proportion of unsaturated to saturated fatty acids, and in the number of double bonds per mole, were greater at sn-2 than at sn-1, except for phosphatidylinositol between 14 and 21 days of age. The pattern of acylation of phosphatidylinositol between 14 and 21 days was thus different from that of phosphatidylcholine and phosphatidylethanolamine. Furthermore, at the three ages investigated, phosphatidylinositol had low and relatively constant levels of unsaturation compared with phosphatidylcholine and phosphatidylethanolamine. The net decrease in phospholipid double bonds per mole in aging cells of L. lipoferus, and previous data, suggest that aging in this yeast is accompanied by a decrease in membrane fluidity.

Regulation by temperature of the chain length of fatty acids in yeast.

Regulation by temperature of the chain length of fatty acids in yeast.