Unsubstituted Fatty Acids Research Articles

Primary Fatty Alcohols Are Major Components of Suberized Root Tissues of Arabidopsis in the Form of Alkyl Hydroxycinnamates.

Suberin is a complex hydrophobic polymer that acts as a barrier controlling water and solute fluxes and restricting pathogen infections. Suberin is deposited immediately outside of the plasmalemma in the cell wall of certain tissues such as endodermis of roots, aerial and underground periderms, and seed coats. Suberin consists of a variety of fatty acid derivatives polymerized with glycerol and phenolics. In this study, we show using liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry techniques that most of the fatty alcohols not covalently linked to the suberin polymer are in the form of alkyl hydroxycinnamates (AHCs), with alkyl caffeates predominating. Such compounds are not restricted to the periderm of mature roots but also are present in the endodermis of younger roots, where they are not extracted by rapid dipping in chloroform. Analysis of several mutants affected in key enzymes involved in the biosynthesis and export of suberin monomers suggests that the formation of the suberin polymer and associated waxes involves common pathways and occurs concomitantly in Arabidopsis (Arabidopsis thaliana) roots. Although fatty alcohols represent only minor components of the suberin polymer in Arabidopsis roots, this study demonstrates that they constitute the major aliphatics of suberin-associated waxes in the form of AHCs. Therefore, our results indicate that esterified fatty alcohols, both soluble and polymerized forms, represent major constituents of Arabidopsis root suberized barriers, being as abundant as α,ω-dicarboxylic and unsubstituted fatty acids. In addition, our results show that suberized layers represent a major sink for acyl-lipid metabolism in Arabidopsis roots.

Identification of an Arabidopsis feruloyl-coenzyme A transferase required for suberin synthesis.

All plants produce suberin, a lipophilic barrier of the cell wall that controls water and solute fluxes and restricts pathogen infection. It is often described as a heteropolymer comprised of polyaliphatic and polyaromatic domains. Major monomers include omega-hydroxy and alpha,omega-dicarboxylic fatty acids, glycerol, and ferulate. No genes have yet been identified for the aromatic suberin pathway. Here we demonstrate that Arabidopsis (Arabidopsis thaliana) gene AT5G41040, a member of the BAHD family of acyltransferases, is essential for incorporation of ferulate into suberin. In Arabidopsis plants transformed with the AT5G41040 promoter:YFP fusion, reporter expression is localized to cell layers undergoing suberization. Knockout mutants of AT5G41040 show almost complete elimination of suberin-associated ester-linked ferulate. However, the classic lamellar structure of suberin in root periderm of at5g41040 is not disrupted. The reduction in ferulate in at5g41040-knockout seeds is associated with an approximate stoichiometric decrease in aliphatic monomers containing omega-hydroxyl groups. Recombinant AT5G41040p catalyzed acyl transfer from feruloyl-coenzyme A to omega-hydroxyfatty acids and fatty alcohols, demonstrating that the gene encodes a feruloyl transferase. CYP86B1, a cytochrome P450 monooxygenase gene whose transcript levels correlate with AT5G41040 expression, was also investigated. Knockouts and overexpression confirmed CYP86B1 as an oxidase required for the biosynthesis of very-long-chain saturated alpha,omega-bifunctional aliphatic monomers in suberin. The seed suberin composition of cyp86b1 knockout was surprisingly dominated by unsubstituted fatty acids that are incapable of polymeric linkages. Together, these results challenge our current view of suberin structure by questioning both the function of ester-linked ferulate as an essential component and the existence of an extended aliphatic polyester.

A Novel Thermostable Arylesterase from the ArchaeonSulfolobus solfataricusP1: Purification, Characterization, and Expression

A novel thermostable arylesterase, a 35-kDa monomeric enzyme, was purified from the thermoacidophilic archaeon Sulfolobus solfataricus P1. The optimum temperature and pH were 94 degrees C and 7.0, respectively. The enzyme displayed remarkable thermostability: it retained 52% of its activity after 50 h of incubation at 90 degrees C. In addition, the purified enzyme showed high stability against denaturing agents, including various detergents, urea, and organic solvents. The enzyme has broad substrate specificity besides showing an arylesterase activity toward aromatic esters: it exhibits not only carboxylesterase activity toward tributyrin and p-nitrophenyl esters containing unsubstituted fatty acids from butyrate (C(4)) to palmitate (C(16)), but also paraoxonase activity toward organophosphates such as p-nitrophenylphosphate, paraoxon, and methylparaoxon. The k(cat)/K(m) ratios of the enzyme for phenyl acetate and paraoxon, the two most preferable substrates among all tested, were 30.6 and 119.4 s(-1) microM(-1), respectively. The arylesterase gene consists of 918 bp corresponding to 306 amino acid residues. The deduced amino acid sequence shares 34% identity with that of arylesterase from Acinetobacter sp. strain ADP1. Furthermore, we successfully expressed active recombinant S. solfataricus arylesterase in Escherichia coli. Together, our results show that the enzyme is a serine esterase belonging to the A-esterases and contains a catalytic triad composed of Ser156, Asp251, and His281 in the active site.

Myelin Lipid Abnormalities in the Aspartoacylase-Deficient Tremor Rat

The high concentration of N-acetylaspartate (NAA) in neurons of the central nervous system and its growing clinical use as an indicator of neuronal viability has intensified interest in the biological function of this amino acid derivative. The biomedical relevance of such inquiries is highlighted by the myelin-associated pathology of Canavan disease, an inherited childhood disorder resulting from mutation of aspartoacylase (ASPA), the NAA-hydrolyzing enzyme. This enzyme is known to be localized in oligodendrocytes with bimodal distribution in cytosol and the myelin sheath, and to produce acetyl groups utilized in myelin lipid synthesis. Loss of this acetyl source in Canavan disease and rodent models such as the tremor rat are thought to account for the observed myelin deficit. This study was undertaken to further define and quantify the specific lipid abnormalities that occur as a result of ASPA deficit in the tremor rat. Employing mass spectrometry together with high performance thin-layer chromatography, we found that myelin from 28-day-old animals showed major reduction in cerebrosides (CB) and sulfatides (Sulf) with unsubstituted fatty acids, and equal if not greater changes in myelin from 7-month-old tremors. Cerebrosides with 2-hydroxyfatty acids showed little if any change at either age; Sulf with 2-hydroxyfatty acids showed no significant change at 28 days, but surprisingly a major increase at 7 months. Two species of phosphatidylcholine, 32:0 and 34:1, also showed significant increase, but only at 28 days. One form of phosphatidylethanolamine, PE36:1, was reduced a modest amount at both ages, whereas the plasmalogen form did not change. The dysmyelination that results from inactivation of ASPA is thus characterized by selective decreases as well as some increases in specific lipids.

Molecular definitions of fatty acid hydroxylases in Arabidopsis thaliana

Towards defining the function of Arabidopsis thaliana fatty acid hydroxylases, five members of the CYP86A subfamily have been heterologously expressed in baculovirus-infected Sf9 cells and tested for their ability to bind a range of fatty acids including unsubstituted (lauric acid (C12:0) and oleic acid (C18:1)) and oxygenated (9,10-epoxystearic acid and 9,10-dihydroxystearic acid). Comparison between these five P450s at constant P450 content over a range of concentrations for individual fatty acids indicates that binding of different fatty acids to CYP86A2 always results in a higher proportion of high spin state heme than binding titrations conducted with CYP86A1 or CYP86A4. In comparison to these three, CYP86A7 and CYP86A8 produce extremely low proportions of high spin state heme even with the most effectively bound fatty acids. In addition to their previously demonstrated lauric acid hydroxylase activities, all CYP86A proteins are capable of hydroxylating oleic acid but not oxygenated 9,10-epoxystearic acid. Homology models have been built for these five enzymes that metabolize unsubstituted fatty acids and sometimes bind oxygenated fatty acids. Comparison of the substrate binding modes and predicted substrate access channels indicate that all use channel pw2a consistent with the crystal structures and models of other fatty acid-metabolizing P450s in bacteria and mammals. Among these P450s, those that bind internally oxygenated fatty acids contain polar residues in their substrate binding cavity that help stabilize these charged/polar groups within their largely hydrophobic catalytic site.

Influence of an Amide Group in Methyl Octadecanoates on the Monolayer Stability

The influence of a hydrogen bond donor and acceptor in the hydrophobic part of an amphiphile on the monolayer stability at the air/water interface is investigated. For that purpose, the amide group is integrated into the alkyl chain. Eight methyl octadecanoates have been synthesized with the amide group in two orientations and in different positions of the alkyl chain, namely, CH3O2C(CH2)m NHCO(CH2)n CH3 (n + m = 14): 1 (m = 1), 3 (m = 2), 5 (m = 3), 7 (m = 14); and CH3O2C(CH2)m CONH(CH2)n CH3: 2 (m = 1), 4 (m = 2), 6 (m = 3), 8 (m = 14). The monolayers have been characterized by their pi/A isotherms, their temperature dependence and Brewster angle microscopy (BAM). Amphiphile 1 with the amide group close to the ester group (m = 1) behaves like an unsubstituted fatty acid ester, while 3, 5, and 7, with the amide group in an intermediate and terminal position, exhibit a two-phase region. The amphiphiles 2, 4, 6, and 8, with a reversed orientation of the amide group, all exhibit a two-phase region with higher plateau pressures and lower collapse pressures than those of 1, 3, 5, and 7. For 7 and 8, domains of the liquid condensed (LC) phase are visualized by BAM in the two-phase region. The liquid expanded (LE)/LC-phase transitions are all exothermic with enthalpies deltaH ranging from -31 to -12 kJ/mol. Comparison with other bipolar amphiphiles indicates that the LC phase is better stabilized by the hydroxy and dihydroxy groups than by the amide group. For model compounds of 1-4, optimized conformers in the LE and LC phases have been determined by density functional theory (DFT) calculations.

Isolation and structure of monomethylated GM3-type ganglioside molecular species from the starfish Luidia maculata.

Two monomethylated GM(3)-Type ganglioside molecular species, 1 and 2, have been obtained from the polar lipid fraction of the chloroform/methanol extract of the starfish Luidia maculata. The structures of these gangliosides have been determined on the basis of chemical and spectroscopic evidence as 1-O-[8-O-methyl-(N-acetyl-alpha-D-neuraminosyl)-(2-->3)-beta-D-galactopyranosyl-(1-->4)-beta-D-glucopyranosyl]-ceramide (1) and 1-O-[8-O-methyl-(N-glycolyl-alpha-D-neuraminosyl)-(2-->3)-beta-D-galactopyranosyl-(1-->4)-beta-D-glucopyranosyl]-ceramide (2). The ceramide moieties were composed of heterogeneous unsubstituted fatty acid, 2-hydroxy fatty acid, sphingosine and phytosphingosine units. Compound 1, designated as LMG-3, represents new ganglioside molecular species. Compound 2 was a known ganglioside molecular species.

Constituents of ophiuroidea. 1. Isolation and structure of three ganglioside molecular species from the brittle star Ophiocoma scolopendrina.

Three ganglioside molecular species, OSG-0 (1), OSG-1 (2), and OSG-2 (3) have been obtained from the polar lipid fraction of the chloroform/methanol extract of the brittle star Ophiocoma scolopendrina. The structures of these gangliosides have been determined on the basis of chemical and spectroscopic evidence as 1-O-[(N-glycolyl-alpha-D-neuraminosyl)-(2-->6)-beta-D-glucopyranosyl]-ceramide (1), 1-O-[8-O-sulfo-(N-acetyl-alpha-D-neuraminosyl)-(2-->6)-beta-D-glucopyranosyll-ceramide (2) and 1-O-[(N-glycolyl-alpha-D-neuraminosyl)-(2-->8)-(N-acetyl- and N-glycolyl-alpha-D-neuraminosyl)-(2-->6)-beta-D-glucopyranosyl]-ceramide (3). The ceramide moieties were composed of heterogeneous unsubstituted fatty acid, 2-hydroxy fatty acid and phytosphingosine units. Compounds 2 and 3 represent new ganglioside molecular species.

Protonophoric Activity of Fatty Acid Analogs and Derivatives in the Inner Mitochondrial Membrane: A Further Argument for the Fatty Acid Cycling Model

The protonophoric (uncoupling) action of various long-chain fatty acids and their derivatives in mitochondria was investigated as related to their ability for rapid transbilayer movement in the inner mitochondrial membrane (flip-flop) and interaction with the ADP/ATP carrier (AAC). Flip-flop was assessed from a rapid decrease of internal mitochondrial pH. It was found that long-chain unsubstituted fatty acids (with the exception of very-long-chain unbranched homologs) and their thia and oxa analogs performed a rapid flip-flop, inhibited AAC activity and increased proton permeability of the inner mitochondrial membrane, resulting in dissipation of mitochondrial membrane potential and increased resting state respiration. Bipolar fatty acid analogs, i.e., those containing a second carboxylic group or OH group(s) at the hydrocarbon tail, phenyl-substituted fatty acid derivatives, and fatty acid analogs containing strongly ionized sulfonyl or sulfate groups instead of the carboxylic group, did not flip-flop and were not uncoupling, although some of them were weak inhibitors of AAC. These results provide further confirmation of the fatty acid cycling model (V. P. Skulachev,FEBS Lett. 294,158–162, 1991) in which the protonophoric function of fatty acids is a result of the spontaneous transbilayer passage of undissociated (protonated) molecules of the fatty acid from the external side of the inner mitochondrial membrane to the matrix side and the AAC-mediated transport of the fatty acid anion in the opposite direction.

Monitoring of lipoprotein oxidation by gas chromatographic analysis of hydroxy fatty acids

We describe a method developed for the quantitative analysis of hydroxy fatty acids derived from fatty acid monohydroperoxides formed during lipoprotein oxidation. The procedure starts with catalytic hydrogenation of the lipid extract, whereby hydroperoxyl groups are converted to hydroxyl groups and double bonds are eliminated, and the risk for lipid oxidation during the rest of the procedure is eliminated. The fatty acids are converted to methyl esters, which are fractionated by gas chromatography on a nonpolar column. The major differences to existing methods are that a mass spectrometer is not required and that the specificity thus lost is replaced by gas chromatography before and after acetylation of the hydroxyl groups. This changes the retention times of the hydroxyacids with respect to the unsubstituted fatty acids moving them to positions usually occupied by trace components only. The method allows quantification of monohydroxy fatty acids derived from 18-, 20- and 22-carbon polyunsaturated fatty acids. Positional isomers are separated from each other to some extent. The method has been mainly used for analysis of hydroperoxides in human low density lipoprotein preparations and for following lipoprotein oxidation in vitro.

Brucella abortus 16S rRNA and lipid A reveal a phylogenetic relationship with members of the alpha-2 subdivision of the class Proteobacteria

On the basis of ribosomal 16S sequence comparison, Brucella abortus has been found to be a member of the alpha-2 subdivision of the class Proteobacteria (formerly named purple photosynthetic bacteria and their nonphototrophic relatives). Within the alpha-2 subgroup, brucellae are specifically related to rickettsiae, agrobacteria, and rhizobiae, organisms that also have the faculty or the obligation of living in close association to eucaryotic cells. The composition of Brucella lipid A suggests a close phylogenetical relationship with members of the alpha-2 group. The chemical analysis of the lipid A fraction revealed that Brucella species contain both glucosamine and diaminoglucose, thus suggesting the presence of a so-called mixed lipid A type. The serological analysis with polyclonal and monoclonal antibodies is in agreement with the existence of mixed lipid A type in B. abortus. The amide-linked fatty acid present as acyl-oxyacyl residues were 3-O-C(16:0)12:0, 3-O-C(16:0)13:0, 3-O-C(16:0)14:0, and 3-O-C(18:0)14:0. The only amide-linked unsubstituted fatty acid detected was 3-OH-C16:0. The ester-linked fatty acids are 3-OH-C16:0, 3-OH-C18:0, C16:0, C17:0, and C18:0. Significant amounts of the large-chain 27-OH-C28:0 were detected together with traces of 25-OH-C26:0 and 29-OH-C30:0. Comparison of the Brucella lipid composition with that of the other Proteobacteria also suggests a close phylogenetical relationship with members of the alpha-2 subdivision. The genealogical grouping of Brucella species with pericellular and intracellular plant and animal pathogens as well as with intracellular plant symbionts suggests a possible evolution of Brucella species from plant-arthropod-associated bacteria.

Gangliosides from the starfishEvasterias echinosoma: identification of a disialoganglioside containing 8-O-methyl-N-acetylneuraminic acid andN-formylgalactosamine

Gangliosides were isolated from the starfishEvasterias echinosoma and their structures were elucidated by chemical and physicochemical methods. Two major gangliosides were found to be disialogangliosides, whose carbohydrate chain is based on the trisaccharide β-N-acylgalactosaminyl-(l→3)-β-galactosyl-(l→4)-β-glucose (acyl is formyl or acetyl), both residue at of 8-O-methyl-N-acetylneuraminic acid being attached to theN-acylgalactosamine residue at positions 3 and 6. The minor components are disialogangliosides with linear carbohydrate chains in which the terminal sialic acid residue is attached to the penultimateN-acetylneuraminic acid residue at positions 4, 8, or 9. The lipid part of the gangliosides consists of sphingenine and unsubstituted fatty acids (mainly, palmitic and stearic acids).

Hematoside with 8-O-methyl-N-glycolylneuraminic acid from the starfishLinckia laevigata

A ganglioside was isolated from the starfishLinckia laevigata, and its structure was elucidated by chemical methods, mass spectrometry, and enzymatic hydrolysis with neuraminidase. The ganglioside is a hematoside containing 8-O-methyl-N-glycolylneuraminic acid, 8-O-Me-Neu5Gc-α2→3-Gal-β1→4-Glc-β1→1-Cer. The lipid part of the ganglioside consists of unsubstituted fatty acids (the major component is palmitic acid) and C18∶1-iso-sphingenine.

Lipids of soil humic acids. II. Residual components after hymatomelanic acid extraction

After separation of the hymatomelanic acid fraction more lipid components can be recovered from humic acids by Soxhlet extraction with other solvents than ethanol (i.e., methylene chloride-methanol). The composition of these remaining mixtures has been investigated on the humic acids of three soils encompassing different properties in terms of pH, carbon content and associated vegetation (a Typic Xerochrept, a Typic Rendoll and a Typic Xerorthent). The hymatomelanic acid fraction of these samples has been studied elsewhere (ref. 1). Unsubstituted fatty acids generally predominate in both successive extracts, although distinct distributions are characteristics in each case. Important qualitative differences have been observed for other components, namely steroidal ketones and hydroxy acids.

Evidence for distinct pathways in rabbit renal brush-border membrane vesicles for the transport of unsubstituted and alpha-hydroxysubstituted aliphatic monocarboxylic acids.

We evaluated the effects of unsubstituted and hydroxymonocarboxylic acids on the kinetics of Na+-dependent L-lactate uptake in brush-border membrane vesicles prepared from the whole cortex of rabbit kidney. Acetate, propionate, and butyrate reversibly inhibited Na+-dependent L-lactate influx with [I]0.5 values of 5.5, 0.50, and 0.25 mM, respectively. Dixon plots (1/V versus acetate, propionate, and butyrate) were curved concavely downward, indicating partial inhibition. The Hill coefficients were approximately 1.0, suggesting that these anions interact at a single site on the Na+-L-lactate cotransporter. Acetate and the two other unsubstituted short-chain fatty acids tested decreased Na+-dependent L-lactate influx by increasing Km and decreasing Vmax, indicating mixed-type inhibition. In contrast, Na+-dependent L-lactate uptake was competitively inhibited by alpha-hydroxybutyrate and D-lactate. Finally, evidence is presented to show that D-lactate and alpha-hydroxybutyrate are mutually exclusive inhibitors of Na+-dependent L-lactate influx. Results from this and recent studies are interpreted as indicating that distinct transport systems serve for unsubstituted and alpha-hydroxymonocarboxylic acids in renal brush-border membrane vesicles.

Biochemical and physicochemical determinations in a premyelin fraction obtained by zonal centrifugation in normal mouse and in dysmyelinating mutants (quaking, shiverer, and myelin-deficient).

Myelin and premyelin material denser than myelin were obtained from quaking (Qk), shiverer (Shi), and myelin-deficient (mld) mutant and control mice, using zonal centrifugation on zonal rotor. On these fractions, we performed biochemical analysis (lipids and fatty acid), and, in parallel, we determined the physical structure of membranes by the spin-label method. The hyperfine splitting constant (2 Tll) was used to determine the order of membranes and their rigidity, and frequency of rotation (Vc) was used to measure fluidity. In control mice, the premyelin material contained a lesser amount of sphingolipids than pure myelin, but the relative proportions between hydroxy- and nonhydroxy-cerebroside and sulfatides were similar in the premyelin material and in pure myelin. The premyelin material contained half the alkanes found in the pure myelin and much less very-long-chain fatty acids. The (2 Tll) was lower in the premyelin material, but the (Vc) was similar in myelin and premyelin material. In mutants, the amount of material recovered in the premyelin fraction was reduced in qk, and increased in both shi and mld. The relative amount of sphingolipids were normal in mld, but not in shi mutants, especially in cerebrosides formed with alpha-hydroxylated fatty acids and sulfatides formed with unsubstituted fatty acids. The absolute amounts of sphingolipids were nearly normal in both shi and mld. In the premyelin fraction from qk mutants, both relative and absolute amounts of sphingolipids were drastically altered. In percentage, cerebrosides and sulfatides formed with nonhydroxyfatty acids were dramatically reduced, and, conversely, cerebrosides and sulfatides formed with hydroxyfatty acids were increased. In terms of absolute amount, only cerebrosides and sulfatides formed with nonhydroxyfatty acids were dramatically reduced. In the premyelin fraction, polyunsaturated fatty acids were increased in shi and mld, but decreased in qk. In this mutant, lignoceric (24:0) and nervonic (24:1) acids were drastically reduced. The amount of alkanes in the premylin material from qk and mld was reduced by 50%. The shi fraction was nearly free of alkanes. The maximal apparent coupling constant (hyperfine splitting constant, 2 Tll) was not affected in the mld and qk mutant, but was reduced in the shi mutant premyelin fraction. The Vc was dramatically increased in the qk, slightly decreased in the shi, and close to control in the mld. This work provides additional data on premyelin material prepared in various neurological mutants using continuous gradients in zonal rotor.(ABSTRACT TRUNCATED AT 400 WORDS)

Double-bond patterns of fatty acids and alcohols in steer and human meibomian gland lipids.

Ozonolysis studies of the monoenes of the fatty chain types in lipids of steer meibomian gland excreta (meibum) have confirmed earlier structural assignments based on gas liquid chromatography (GLC) retention data and have assisted in assigning complete structures to a group of recently identified omega-hydroxy fatty acids. The omega-hydroxy acids include straight-chain monoenoic acids (85%), saturated anteiso and iso acids (13%), monoenoic acids of the latter group (1%) and, finally, saturates of the normal monoenoic acids (1%). All the fatty chains of meibum can be biosynthesized by a unified process of chain buildup to primary chain lengths of 12:0-20:0 for the straight evens, with 16:0 predominating, 13:0-21:0 for the straight odds with 17:0 predominating, i16:0 to i28:0 for the iso and ai17:0 to ai29:0 for the anteiso chain types; then delta 9 desaturation of each of these chain types: and finally chain elongation of 1-10 C2 units. Some chain degradation may also occur. The meibum lipid components involved are unsubstituted fatty acids, alpha-OH fatty acids, alpha-OH fatty acids, omega-OH fatty acids, fatty alcohols and some other lipid components incompletely characterized. The carbon skeletons are straight even, straight odd, iso and anteiso except that the alpha-OH fatty acids are only straight even and straight odd and these chains are not elongated. All fatty chains are almost entirely saturated and monoenoic, the polyenes occurring in only trace amounts. Biosynthesis of the fatty chains of human meibum evidently occurs similarly, except that considerably more 18:0 than 16:0 fatty acids are built up by the fatty acid synthetase, before desaturation and extension.

Biochemical studies of metachromatic leukodystrophy in three siblings.

Biochemical analyses were performed on cerebral biopsies from three siblings with metachromatic leukodystrophy, and from autopsy tissue obtained 6 months later. The lipids of all gray matter samples were relatively normal, with the exception of an elevated sulfatide: cerebroside ratio. The white matter samples were grossly abnormal and showed a progression in severity of biochemical abnormalities with duration of the disease. Sulfatides were 4-8-fold higher than normal, and the ratio of cerebrosides to sulfatides ranged from 0.13 to 0.26, compared to the normal value of about 4.0. Myelin was isolated in very low yield, but had normal morphology. As others have reported, it had the same chemical defect as whole white matter; sulfatides were 7-8 times higher than normal and cerebrosides were reduced by more than half. The fatty acid compositions of the myelin sphingolipids were found to be of much longer average chain length than those in affected white matter. In myelin, the unsubstituted fatty acids of cerebrosides and sphingomyelin had a higher percentage of short chains than found in normal myelin, but were less abnormal than those in whole white matter, whereas the unsubstituted and alpha-hydroxy acids of sulfatides and the alpha-hydroxy acids of cerebrosides were not deficient in long chains. These data indicate that there are at least two compartments of sphingolipids in MLD white matter, each having different average chain lengths.

The composition of the skin surface lipids of the gerbil

The skin surface lipids of the gerbil were found to consist sterol esters (10%), wax diesters (36.3%), triacylglycerol (26.1%), free fatty alcohols (8.8%), free fatty acids (5.4%), cholesterol (8.4%) and polar lipids (5%). The wax diesters, identified as Type II, were made up of saturated 1,2-diols with odd carbon number, esterified with two molecules of unsubstituted fatty acids with even carbon number. Both the triacylglycerols and the free fatty acid fractions had saturated and unsaturated components. The free and esterified sterols were all cholesterol. The sterol esters contained saturated monoenoic and dienoic fatty acids, with both straight- and branched-chain components. The fatty alcohols were all straight-chain in structure, mostly of even carbon number. Comparison of these results with those previously reported for other species, indicates that the gerbil skin surface lipids are unique in that they contain diacyl alkane diols and fatty alcohols, both of which consist exclusively of saturated components.

Comparison of the inhibition by methylmercury and triethyllead of galactolipid accumulation in rat brain

Methylmercury chloride (MeHg) and triethyllead chloride (Et 3Pb) interfere with the myelin deposition in young rats. In order to establish how myelin synthesis and development are affected by these neurotoxins, we have investigated the synthesis of myelin galactolipids using two different systems: (1) slices of cerebellum from 2-week-old rats, (2) enzyme preparations from rat brain. MeHg (50 μ m) or Et 3Pb (5 μ m) gave maximum inhibition of the uptake of 35SO 4 by sulfatides (63%). The [ 3H]serine uptake by cerebrosides with normal unsubstituted fatty acids (NFA) was inhibited up to 45% at 70 and 7 μ m of MeHg and Et 3Pb, respectively, after incubation of the slices for 16 hr in an Eagle basal medium at 37°C. At the same concentrations the inhibition of [ 3H]serine uptake in cerebrosides with α-hydroxy fatty acids (HFA) was about 35%. MeHg (50–100 μ m) inhibited UDPgalactose:ceramide galactosyltransferase (CGalT) and phosphoadenosine-5′-phosphosulfate:cerebroside sulfotransferase (CST) activities up to 50%, while the inhibition with Et 3Pb was about 30% at 2.5 m m for the enzymes.