Degradation of 3-methylpyridine and 3-ethylpyridine by Gordonia nitida LE31

Cells of Gordonia nitida LE31 grown on 3-methylpyridine degraded 3-ethylpyridine without a lag time and vice versa. Cyclic intermediates were not detected, but formic acid was identified as a metabolite. Degradation of levulinic acid was induced in cells grown on 3-methylpyridine and 3-ethylpyridine. Levulinic aldehyde dehydrogenase and formamidase activities were higher in cells grown on 3-methylpyridine and 3-ethylpyridine than in cells grown on acetate. These data indicate that 3-methylpyridine and 3-ethylpyridine were degraded via a new pathway involving C-2-C-3 ring cleavage.     

Biodegradation of 2-methyl, 2-ethyl, and 2-hydroxypyridine by an Arthrobacter sp. isolated from subsurface sediment

A bacterium capable of degrading 2-methylpyridine was isolated by enrichment techniques from subsurface sediments collected from an aquifer located at an industrial site that had been contaminated with pyridine and pyridine derivatives. The isolate, identified as an Arthrobacter sp., was capable of utilizing 2-methylpyridine, 2-ethylpyridine, and 2-hydroxypyridine as primary C, N, and energy sources. The isolate was also able to utilize 2-, 3-, and 4-hydroxybenzoate, gentisic acid, protocatechuic acid and catechol, suggesting that it possesses a number of enzymatic pathways for the degradation of aromatic compounds. Degradation of 2-methylpyridine, 2-ethylpyridine, and 2-hydroxypyridine was accompanied by growth of the isolate and release of ammonium into the medium. Degradation of 2-methylpyridine was accompanied by overproduction of riboflavin. A soluble blue pigment was produced by the isolate during the degradation of 2-hydroxypyridine, and may be related to the diazadiphenoquinones reportedly produced by other Arthrobacter spp. when grown on 2-hydroxypyridine. When provided with 2-methylpyridine, 2-ethylpyridine, and 2-hydroxypyridine simultaneously, 2-hydroxypyridine was rapidly and preferentially degraded; however there was no apparent biodegradation of either 2-methylpyridine or 2-ethylpyridine until after a seven day lag. The data suggest that there are differences between the pathway for 2-hydroxypyridine degradation and the pathway(s) for 2-methylpyridine and 2-ethylpyridine.     

Aerobic biodegradation of 4-methylpyridine and 4-ethylpyridine by newly isolated Pseudonocardia sp. strain M43

A filamentous bacterium capable of utilizing 4-methylpyridine and 4-ethylpyridine as the sole source of carbon, nitrogen and energy was isolated from sludge. The organism, designated as strain M43, clustered most closely with members of the genus Pseudonocardia by 16S rRNA gene sequence analysis. During the degradation of 4-methylpyridine and 4-ethylpyridine, c. 60% of nitrogen in the pyridine ring was released as ammonia. Metabolite analyses showed that 2-hydroxy-4-methylpyridine and 2-hydroxy-4-ethylpyridine were transiently accumulated during the degradation of 4-methylpyridine and 4-ethylpyridine, respectively. Strain M43 was also able to degrade pyridine, 3,4-dimethylpyridine, 4-carboxypyridine and 2-hydroxy-4-methylpyridine. The results indicate that degradation of 4-methylpyridine and 4-ethylpyridine by strain M43 proceeded via initial hydroxylation.     

Microbial Decomposition of alpha-Picoline

An organism, which degrades alpha-picoline but also utilizes 2-ethylpyridine or piperidine as alternative growth substrates, has been isolated from soil and characterized as arthrobacter sp. alpha-picoline-grown cells oxidize 2-ethylpyridine and vice versa. Other pyridine derivatives tested are neither utilized as growth substrates nor oxidized by the organism. alpha-Picolinate and 2-hydroxy-6-methylpyridine are not metabolized, indicating that degradation is neither initiated by methyl oxidation nor by hydroxylation in the 6-position of pyridine ring. Succinate semi-aldehyde and pyruvate accumulate when alpha-picoline oxidation by resting cell suspensions is blocked by semicarbazide. The Arthrobacter grown on alpha-picoline rapidly oxidizes succinate semi aldehyde...     

Degradation of pyridine and 4-methylpyridine by <Emphasis Type="Italic">Gordonia terrea</Emphasis> IIPN1

Gordonia terrea IIPN1 was isolated and characterized from soils collected at petroleum drilling sites. The strain was able to catabolize pyridine and 4-methylpyridine as sole carbon and nitrogen source. The strain failed to catabolize other pyridine derivatives. Growing cells completely degraded 30 mM of pyridine in 120 h with growth yield of 0.29 g g(-1). Resting Cells grown on 5 mM pyridine degraded 4-methylpyridine without a lag time and vice versa. Supplementary carbon and nitrogen source did not significantly change the specific growth rate and degradation rate by the resting cells.     

Inverse correlation between combined mutagenicity in Salmonella typhimurium and strength of coordinate bond in mixtures of cobalt(II) chloride and 4-substituted pyridines

Cobalt(II) chloride (CoCl₂), non-mutagenic by itself, has been tested for mutagenic activity in the presence of 4-substituted pyridines in the test strains of Salmonella typhimurium. CoCl₂ was found to be mutagenic in strains TA1537 and TA2637, when combined pyridine, with methyl isonicotinate, 4-methylpyridine, 4-ethylpyridine, 4-chloropyridine or 4-bromopyridine. Mixtures of CoCl₂ and isonicotinic acid, 4-cyanopyridine, 4-aminopyridine, or 4-dimethylaminopyridine exhibited no mutagenicity. Judging from the spectral observations, such combined mutagenicity may be due to the formation of moderate to weak complexes between these compounds and the Co(II) cation.     

5-Dehydro-3-deoxy-D-arabino-heptulosonic acid 7-phosphate. An intermediate in the 3-dehydroquinate synthase reaction.

3-Dehydroquinate synthase was purified to homogeneity from Escherichia coli. It was found to be a single polypeptide chain of Mr = approximately 57,000. Reaction mixtures of pure enzyme and the substrate, 3-deoxy-D-arabino-heptulosonic acid 7-phosphate, were incubated for short times and treated with NaB3H4. The resulting 3-deoxyheptonic acid 7-phosphate was degraded with sodium periodate, and formic acid representing C-5 of the substrate was isolated. The presence of 3H in the formate corresponding to 15% of the enzyme was interpreted as indicating a 5-dehydro derivative of the substrate as an intermediate of the reaction. Quinic acid, resulting from reduction of 3-dehydroquinate with NaB3H4, was also isolated and degraded with periodate. The formate from C-4 of the quinate was unlabeled, indicating that 3,4-bisdehydroquinate is not an intermediate.     

Gluconate Catabolism in Rhizobium japonicum

Gluconate catabolism in Rhizobium japonicum ATCC 10324 was investigated by the radiorespirometric method and by assaying for key enzymes of the major energy-yielding pathways. Specifically labeled gluconate gave the following results for growing cells, with values expressed as per cent (14)CO(2) evolution: C-1 = 93%, C-2 = 57%, C-3 = 30%, C-4 = 70%, C-6 = 39%. The preferential release of (14)CO(2) from C-1 and C-4 indicate that gluconate is degraded primarily by the Entner-Doudoroff pathway but the inequalities between C-1 and C-4 and between C-3 and C-6 indicate that another pathway(s) also participates. The presence of gluconokinase and a system for converting 6-phosphogluconate to pyruvate also indicate a role for the Entner-Doudoroff pathway. The extraordinarily high yield of (14)CO(2) from C-1 labeled gluconate suggests that the other participating pathway is a C-1 decarboxylative pathway. The key enzyme of the pentose phosphate pathway, 6-phosphogluconate dehydrogenase, could not be demonstrated. Specifically labeled 2-ketogluconate and 2,5-diketogluconate were oxidized by gluconate grown cells and gave ratios of C-1 to C-6 of 2.73 and 2.61, respectively. These compare with a ratio of 2.39 obtained with specifically labeled gluconate. Gluconate dehydrogenase, the first enzyme in the ketogluconate pathway found in acetic acid bacteria, was found. Oxidation of specifically labeled pyruvate, acetate, succinate, and glutamate by gluconate-grown cells yielded the preferential rates of (14)CO(2) evolution expected from the operation of the tricarboxylic acid cycle. These data are consistent with the operation of the Entner-Doudoroff pathway and tricarboxylic acid cycle as the primary pathways of gluconate oxidation in R. japonicum. An ancillary pathway for the initial breakdown of gluconate would appear to be the ketogluconate pathway which enters the tricarboxylic acid cycle at alpha-ketoglutarate.     

Coordinate regulation of cholesterol synthesis and 3-hydroxy-3-methylglutaryl coenzyme A synthase but not 3-hydroxy-3-methylglutaryl coenzyme A reductase in C-6 glia

The effects on cholesterol biosynthesis of growth of cultured C-6 glial cells in serumfree medium ± supplementation with linoleic or linolenic acid were studied. Markedly higher activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase, EC 1.1.1.34) were observed in cells grown in linoleate- or linolenate-supplemented versus nonsupplemented medium. After 48 h HMG-CoA reductase activities were two-and four-fold higher in cells supplemented with 20 and 100 μm linoleate, respectively. The increase in activity became apparent after 24 h and was marked after 48 h. Rates of incorporation of [¹⁴C]acetate or ³H₂O into sterols did not reflect the changes in reductase activity. Thus, in cells supplemented with 50 μm linoleate for 24 and 48 h rates of incorporation of [¹⁴C]acetate were 75–80% lower than rates in nonsupplemented cells. This difference resulted because over the first 24 h of the experiment a fivefold increase in the rate of sterol synthesis occurred in the nonsupplemented cells, whereas essentially no change occurred in the linoleate-supplemented cells; little further change occurred between 24 and 48 h in the nonsupplemented and the linoleate-supplemented cells. That the difference in sterol synthesis under these experimental conditions could be mediated at the level of HMG-CoA synthase (EC 4.1.3.5) was suggested by two series of findings, i.e., first, similar quantitative and temporal changes in the activity of this enzyme, and, second, no change in the activity of acetoacetyl-CoA thiolase (EC 2.3.1.9) or the incorporation of [¹⁴C]mevalonate into sterols. Thus, the data suggest that HMG-CoA synthase, and not HMG-CoA reductase, may direct the rate of cholesterol biosynthesis under these conditions of serum-free growth ± supplementation with polyunsaturated fatty acid.     

Heterologous Production of Dihomo-γ-Linolenic Acid in Saccharomyces cerevisiae

To make dihomo-γ-linolenic acid (DGLA) (20:3n-6) in Saccharomyces cerevisiae, we introduced Kluyveromyces lactis Δ12 fatty acid desaturase, rat Δ6 fatty acid desaturase, and rat elongase genes. Because Fad2p is able to convert the endogenous oleic acid to linoleic acid, this allowed DGLA biosynthesis without the need to supply exogenous fatty acids on the media. Medium composition, cultivation temperature, and incubation time were examined to improve the yield of DGLA. Fatty acid content was increased by changing the medium from a standard synthetic dropout medium to a nitrogen-limited minimal medium (NSD). Production of DGLA was higher in the cells grown at 15°C than in those grown at 20°C, and no DGLA production was observed in the cells grown at 30°C. In NSD at 15°C, fatty acid content increased up until day 7 and decreased after day 10. When the cells were grown in NSD for 7 days at 15°C, the yield of DGLA reached 2.19 μg/mg of cells (dry weight) and the composition of DGLA to total fatty acids was 2.74%. To our knowledge, this is the first report describing the production of polyunsaturated fatty acids in S. cerevisiae without supplying the exogenous fatty acids.     

A novel pathway for the biodegradation of 3-nitrotoluene in Pseudomonas putida

Abstract: 3-Nitrotoluene was degraded when incubated with the resting cells of Pseudomonas putida OU83. Most of the 3-nitrotoluene (70%) was metabolized via reduction of the nitro group to form 3-aminotoluene (3-AT). A minor portion (30%) was degraded through a novel pathway involving oxidation of 3-NT to form 3-nitrophenol through a series of intermediary metabolites: 3-nitrobenzyl alcohol, 3-nitrobenzaldehyde and 3-nitrobenzoic acid. Degradation of 3-nitrophenol occurred with the formation of a transient intermediary metabolite, hydroxynitroquinone, which was further degraded with the near stoichiometric release of nitrite into the medium. 3-Nitrotoluene-induced cells showed increased oxygen consumption with 3-nitrotoluene, 3-nitrobenzaldehyde, 3-nitrobenzoate, and 3-nitrophenol as substrates in comparison to uninduced cells. Cell extracts prepared from strain OU83 contained benzylalcohol dehydrogenase and benzaldehyde dehydrogenase activities. The experimental evidence suggests a novel pathway for the degradation of 3-NT in which C-1 elimination is catalyzed by a cofactor-independent deformylase, rather than a decarboxylase or dioxygenase.     

Suppression of glucocorticoid-induced elevation of alkaline phosphatase in C-4-1 cells by inhibitors of 3-hydroxy-3-methylglutaryl-coenzymea reductase and reversal of the suppression by mevalonate

Cell line C-4-a which produces alkaline phosphatase (EC 3.1.1.4) of the placental type in response to glucocorticoids was grown in the presence of inhibitors of mevalonate formation for periods ranging from 1 to 4 days. When C-4-1 cells were incubated in the presence of 25-hydroxycholesterol (1 μM) or compactin (11.6 μM) the induction of alkaline phosphatase by 0.2 μM dexamethasone was supressed. This suppression could be partially prevented by the addition of mevalonolactone to the growing culture. The reversal effect by mevalonate was most evident with compactin, a well known competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. In contrast, the effect of tunicamycin which inhibits N-linked protein glycosylation and also prevents alkaline phosphatase induction by glucocorticoids could not be reversed by mevalonate. These results implicate mevalonate in alkaline phosphatase induction, possibly through its role as a precursor of dolichols.     

Studies on Cell Wall of Alkalophilic Bacillus

Cell walls of alkalophilic Bacillus No. C-125 and No. A-59 which grew in different pH conditions were prepared and analyzed. In the walls from cells grown at pH 10.3 (pH 10.3-cell wall) and the walls from cells grown at pH 7.5 (pH 7.5-cell wall) of the alkalophilic bacilli, the contents of neutral sugar and phosphorus were low as compared with those of Bacillus subtilis 6160, while uronic acid and amino acids were abundant. The uronic acid content of the pH 10.3-cell walls was higher than that of the pH 7.5-cell walls in both strains. The insoluble fraction (peptidoglycan) of cell walls of Bacillus No. C-125 consisted of muramic acid, glutamic acid, alanine, diaminopimelic acid and glucosamine as in neutrophilic bacilli. In the TCA soluble fraction of pH 10.3-cell walls of Bacillus No. C-125, uronic acid was a polymer of glucuronic acid containing a small amount of hexosamine, and 2/3 of the ninhydrin positive material was glutamic acid which was derived mainly from poly γ-L-glutamic acid.     

Degradation of phenanthrene and anthracene by Nocardia otitidiscaviarum strain TSH1, a moderately thermophilic bacterium

Aims:  The metabolism of phenanthrene and anthracene by a moderate thermophilic Nocardia otitidiscaviarum strain TSH1 was examined.
Methods and Results:  When strain TSH1 was grown in the presence of anthracene, four metabolites were identified as 1,2-dihydroxy-1,2-dihydroanthracene, 3-(2-carboxyvinyl)naphthalene-2-carboxylic acid, 2,3-dihydroxynaphthalene and benzoic acid using gas chromatography-mass spectrometry (GC-MS), reverse phase-high performance liquid chromatography (RP-HPLC) and thin-layer chromatography (TLC). Degradation studies with phenanthrene revealed 2,2'-diphenic acid, phthalic acid, 4-hydroxyphenylacetic acid, o -hydroxyphenylacetic acid, benzoic acid, a phenanthrene dihydrodiol, 4-[1-hydroxy(2-naphthyl)]-2-oxobut-3-enoic acid and 1-hydroxy-2-naphthoic acid (1H2NA), as detectable metabolites.
Conclusions:  Strain TSH1 initiates phenanthrene degradation via dioxygenation at the C-3 and C-4 or at C-9 and C-10 ring positions. Ortho -cleavage of the 9,10-diol leads to formation of 2,2'-diphenic acid. The 3,4-diol ring is cleaved to form 1H2NA which can subsequently be degraded through o -phthalic acid pathway. Benzoate does not fit in the previously published pathways from mesophiles. Anthracene metabolism seems to start with a dioxygenation at the 1 and 2 positions and ortho -cleavage of the resulting diol. The pathway proceeds probably through 2,3-dicarboxynaphthalene and 2,3-dihydroxynaphthalene. Degradation of 2,3-dihydroxynaphthalene to benzoate and transformation of the later to catechol is a possible route for the further degradation of anthracene.
Significance and Impact of the Study:  For the first time, metabolism of phenanthrene and anthracene in a thermophilic Nocardia strain was investigated.     

The Binding of Indole-3-acetic Acid and 3-Methyleneoxindole to Plant Macromolecules

Homogenates of pea (Pisum sativum L., var. Alaska) seedlings exposed to ¹⁴C-indole-3-acetic acid or ¹⁴C-3-methyleneoxindole, an oxidation product of indole-3-acetic acid, were extracted with phenol. In both cases 90% of the bound radioactivity was found associated with the protein fraction and 10% with the water-soluble, ethanol-insoluble fraction. The binding of radioactivity from ¹⁴C-indole-3-acetic acid is greatly reduced by the addition of unlabeled 3-methyleneoxindole as well as by chlorogenic acid, an inhibitor of the oxidation of indole-3-acetic acid to 3-methyleneoxindole. Chlorogenic acid does not inhibit the binding of ¹⁴C-3-methyleneoxindole. The labeled protein and water-soluble, ethanol-insoluble fractions of the phenol extract were treated with an excess of 2-mercaptoethanol. Independently of whether the seedlings had been exposed to ¹⁴C-indole-3-acetic acid or ¹⁴C-3-methyleneoxindole, the radioactivity was recovered from both fractions in the form of a 2-mercaptoethanol-3-methyleneoxindole adduct. These findings indicate that 3-methyleneoxindole is an intermediate in the binding of indole-3-acetic acid to macromolecules.     

Identification of a Unique Radical S-Adenosylmethionine Methylase Likely Involved in Methanopterin Biosynthesis in Methanocaldococcus jannaschii

Methanopterin (MPT) and its analogs are coenzymes required for methanogenesis and methylotrophy in specialized microorganisms. The methyl groups at C-7 and C-9 of the pterin ring distinguish MPT from all other pterin-containing natural products. However, the enzyme(s) responsible for the addition of these methyl groups has yet to be identified. Here we demonstrate that a putative radical S-adenosyl-l-methionine (SAM) enzyme superfamily member encoded by the MJ0619 gene in the methanogen Methanocaldococcus jannaschii is likely this missing methylase. When MJ0619 was heterologously expressed in Escherichia coli, various methylated pterins were detected, consistent with MJ0619 catalyzing methylation at C-7 and C-9 of 7,8-dihydro-6-hydroxymethylpterin, a common intermediate in both folate and MPT biosynthesis. Site-directed mutagenesis of Cys77 present in the first of two canonical radical SAM CX₃CX₂C motifs present in MJ0619 did not inhibit C-7 methylation, while mutation of Cys102, found in the other radical SAM amino acid motif, resulted in the loss of C-7 methylation, suggesting that the first motif could be involved in C-9 methylation, while the second motif is required for C-7 methylation. Further experiments demonstrated that the C-7 methyl group is not derived from methionine and that methylation does not require cobalamin. When E. coli cells expressing MJ0619 were grown with deuterium-labeled acetate as the sole carbon source, the resulting methyl group on the pterin was predominantly labeled with three deuteriums. Based on these results, we propose that this archaeal radical SAM methylase employs a previously uncharacterized mechanism for methylation, using methylenetetrahydrofolate as a methyl group donor.     

Glycoprotein-bound large carbohydrates of early embryonic cells: structural characteristic of the glycan isolated from F9 embryonal carcinoma cells

The high-molecular-weight glycopeptides characteristic of early embryonic cells were isolated from F9 embryonal carcinoma cells grown in vitro and also from the cells grown in vivo as subcutaneous tumors. The two preparations had similar carbohydrate compositions. The major components were galactose and N-acetylglucosamine (molar ratio 1:0.86) in the glycan isolated from the cultured cells. In addition, small amounts of fucose, N-acetylgalactosamine and mannose were present. The glycan from the in vitro grown cells was found to have a molecular weight of more than 10,000 by gel filtration after mild alkaline treatment or hydrazinolysis. The structural characteristics of the core portion of the glycan were studied by using the radioactively labeled glycopeptide from the in vitro grown cells. Methylation analysis provided the following informations. 1) The glycan was highly branched at galactosyl residues. 2) Large numbers of galactosyl residues were also present at non-reducing termini. 3) Monosubstitution of galactose occurred at C-3. 4) Glucosamine residues were mainly monosubstituted. That the disaccharide GlcNAc-Gal was the major structural unit of the glycan was suggested by the isolation of the deacetylated disaccharide after alkaline thiophenol cleavage followed by acid hydrolysis. Furthermore, methylation analysis of the glycan from the in vivo grown tumors indicated that monosubstitution of glucosamine occurred at C-4 and that disubstitution of galactose occurred at least mainly at C-3 and C-6. We propose that the basic structural unit of the core portion is 4GlcNAc 1 leads to 3Gal, and that the galactosyl residue serves as a branching point at C-6. Thus, the structural unit of the core portion of the large glycan appears to be the same as that of lactosaminoglycans found in adult cells.     

The stereochemistry of biosynthesis of decaprenoxanthin in a cell-free system

Intact cells of Flavobacterium dehydrogenans grown on glucose or acetate did not incorporate mevalonic acid-[¹⁴C]. After treatment with lysozyme the protoplasts were lysed by sonication in a dilute medium containing mevalonic acid-[¹⁴C] and the cell-free system produced incorporated label into uncyclized C₄₀, monocyclic C₄₅ and bicyclic C₅₀ carotenoids of which decaprenoxanthin was the most abundant.With mevalonate-[2-¹⁴C,4R-4-³H₁] the ¹⁴C:³H ratios of the carotenoids showed that the hydrogen atoms at C-2 and C-6 of the ring and that at C-3 of the 1-hydroxy, 2-methyl but-2-ene-4-yl residues of decaprenoxanthin were derived from the 4-pro-R hydrogen atom of mevalonic acid.Mevalonate-[2-¹⁴C,2R-2-³H₁] and mevalonate-[2-¹⁴C,2S-2-³H₁] gave ratios which showed that the C-4 hydrogen atoms of decaprenoxanthin were derived from the 2-pro-S hydrogen atom of mevalonic acid.     

Conversion of ecdysone and 20-hydroxyecdysone into 3-dehydroecdysteroids is a major pathway in third instar Drosophila melanogaster larvae

Ecdysone and 20-hydroxyecdysone metabolism was investigated in third instar Drosophila larvae both in vivo by injecting radiolabelled ecdysteroids and in vitro by incubating various tissues with labelled ecdysteroids.Ecdysone metabolism proceeds through different pathways: (1) C-20 hydroxylation; (2) C-26 hydroxylation and C-26 oxidation leading to the formation of 26-hydroxyecdysteroids (26-hydroxyecdysone and 20,26-dihydroxyecdysone) and acidic compounds (ecdysonoic acid and 20-hydroxyecdysonoic acid); C-3 oxidation and C-3 epimerization then conjugation leading to the formation of 3-dehydrocompounds (3-dehydroecdysone and 3-dehydro-20-hydroxyecdysone), 3-epimers (3-epiecdysone and 3-epi-20-hydroxyecdysone) and conjugates (only one conjugate was tentatively characterized as 3-epi-20-hydroxyecdysone-3-phosphate). 3-Dehydrocompounds are the major metabolites formed in third instar Drosophila larvae and C-3 oxidation occurs in various tissues. Experiments using tritiated cholesterol provided evidence that 3-dehydroecdysone and 3-dehydro-20-hydroxyecdysone are true endogenous ecdysteroids in Drosophila larvae.     

The manipulation of fatty acid composition in L-M cell monolayers supplemented with cyclopentenyl fatty acids

Mouse L-M fibroblasts, grown in a serum-free medium, were supplemented with fatty acids of 16 and 18 carbon chain lengths that contain a cyclopentene ring in the ω position. These fatty acids, unnatural to mammalian systems, were incorporated into the major lipid classes of L-M fibroblasts. Supplementation with the cyclopentenyl fatty acids caused an accumulation of neutral glycerolipids and marked inhibition of cell growth. Following the addition of supplement, the cells became more rounded. Of particular interest was the fact that the phospholipid fraction isolated from treated cells contained cyclic fatty acids that accounted for as much as 24% of the total phospholipid acyl groups. Unlike the pattern of distribution displayed by endogenous natural monoenes, the majority of the cyclic acid present was esterified in the sn-1 position of both phosphatidylcholine and phosphatidylethanolamine. The 18-carbon cyclic fatty acid [chaulmoogric acid, 13-(2-cyclopenten-1-yl)tridecanoic acid] was incorporated at the expense of the endogenous C-16:0, C-18:0, and C-18:1 fatty acids of the glycerophospholipids. The esterification altered the ratio of saturated to unsaturated acyl groups in the cellular phospholipids. No biochemical modification of chaulmoogric acid was detected.Our results imply that incorporation of unnatural fatty acid analogs, such as chaulmoogric acid, into cellular membranes would alter the functional properties of biological membranes that are dependent on membrane fluidity and structural organization.