Incorporation of labelled glycerols into ether lipids in Caldariella acidophila

The lipids of Caldariella acidophila, an extreme thermophile member of the new archaebacteria group, are macrocyclic tetraethers. They are made up of two glycerol molecules (or one glycerol and one nonitol) bridged through ether linkages by two C₄₀16,16′-biphytanyl chains. To elucidate the biosynthesis of the glycerol moiety of these tetraethers and the mechanism of glycerol ether assembly, labelled [U-¹⁴C, 1(3)-³H]glycerol and [U-¹⁴C, 2-³H]glycerol, were fed to C. acidophila. Both precursors were selectively incorporated with high efficiency, and without any change in the ³H/¹⁴C ratio, in the glycerol moiety of tetraethers. These results suggest that the ether forming step in the biosynthesis of tetraether lipids of C. acidophila, occurs without any loss of hydrogen from any of the glycerol carbons which in turn could be directly alkylated by geranylgeranyl pyrophosphate. The incorporation of radioactivity in the isoprenoid chains and into nonitol is also analysed.     

The caldariella group of extreme thermoacidophile bacteria: Direct comparison of lipids in Sulfolobus,Thermoplasma, and the MT strains

It is shown that the lipids from 5 extreme thermoacidophile bacteria of the Caldariella group—2 isolates of Sulfolobus acidocaldarius, one of Thermoplasma acidophila, and 2 of the MT series—are all based on the same type of cyclic diether combining glycerol and one of a series of very unusual C₄₀ isoprenoid diols. The relative proportions of the different C₄₀ components in each isolate have been determined.     

13C-NMR assignments and biosynthetic data for the ether lipids of Caldariella

Fully assigned ¹³C-NMR spectra confirm the C₄₀ (16,16 -biphytanyl) structures of the alkyl chains in the ether lipids of extreme thermoacidophile bacteria of the Caldariella group. The incorporations of ¹³C- and ₁₄C- labelled acetate and mevalonate provide further structural confirmation and define their biosynthetic origin.     

A range of ether core lipids from the methanogenic archaebacterium Methanosarcina barkeri

The core ether lipids of the methanogenic archaebacterium Methanosarcina barkeri were found to consist of C₂₀,C₂₀ glycerol diether and trace amounts of C₂₀,C₂₅ glycerol diether, C₂₀ glycerol monoether, C₄₀,C₄₀ diglycerol tetraethers with 1–3 cyclopentane rings, and a novel C₂₀,C₂₀ tetritol diether.     

Purification and characterization of mononocardomycoloylglycerol from Nocardia rhodochrous

A component of the acetone-soluble lipids of Nocordia rhodochrous grown on glycerol, was purified by column chromatography on silicic acid and characterized by infrared, nuclear magnetic resonance spectroscopy, optical rotation measurement and product identification after alkaline hydrolysis. Glycerol was the sole water-soluble component and nocardomycolic acids with chain lengths ranging from C₄₀ to C₄₄ were the constituent fatty acids identified. On the basis of the evidence obtained, the substance isolated from N. rhodochrous is identified as a mixture of mononocardomycoloylglycerols in which nocardomycolic acids are bound to one of the primary hydroxyl groups of the glycerol molecule.     

Structure of calditol,a new branched-chain nonitol,and of the derived tetraether lipids in thermoacidophile archaebacteria of the Caldariella group

A second category of membrane lipids in extreme thermoacidophile archaebacteria of the Caldariella group is based on the same type of macrocyclic tetraether, incorporating two 16,16′-biphytanyl chains, as those described earlier, but only one of the hydrophilic components is glycerol; the second hydrophilic component is calditol, a unique branched-chain nonitol. It is also shown that in the biphytanyl chains there can be up to 4 cyclopentane rings whose location is demonstrated.     

Effect of isoprenoid cyclization on the transition temperature of lipids in thermophilic archaebacteria

The plasma membrane of Caldariella acidophila, an extreme thermophilic archaebacterium, is characterized by unusual bipolar lipids. They are based on two C₄₀ ω-ω′ biphytanyl residues, with up to four cyclopentane rings per chain linked to either two glycerols (symmetric lipid) or to one glycerol and to one branched-chain nonitol (asymmetric lipid). When C. acidophila is grown at various temperatures, these lipids show a degree of cyclization of the biphytanyl components which increases as the environmental temperature increases. The rôle of cyclization in determining the temperature adaptation is studied on three lipid samples presenting four, five and six cyclopentane rings per molecule, respectively. Differential scanning calorimetry on the dry asymmetric sample as well as conductance and capacitance measurements on black films have been performed. Both sets of measurements indicate the presence of thermal transitions, three in the hydrated compounds, two in the dry system. The latter are shifted towards higher temperature values as the number of cycles increases. Calorimetric measurements show that two of these transitions are strictly related to the presence of nonitol-containing polar heads. In fact, only a single 10-fold higher transition is detected in the homologous lipid bearing two glycerol polar heads, in the dry as well as in the hydrated form. It is suggested that the two higher-temperature thermal transitions, observed on warming the sample, are induced by the breaking of hydrogen bonds between the nonitol-containing polar heads. By contrast, the lower temperature transition, present only in the hydrated compound and similar to that exhibited by the symmetrical sample, is due to a partial melting of the hydrophobic core. The large change in capacitance observed near the higher transition points by lowering temperature would thus correspond to variations in the dielectric constant due to formation of hydrogen bonds.     

Structural regularities in tetraether lipids of Caldariella and their biosynthetic and phyletic implications

Individual di(biphytanyl) diglycerol tetraether lipids from thermoacidophile archaebacteria of the Caldariella series, with differently cyclized biphytanyl components, are separated and shown to have structures 8–12, with the glycerol and biphytanyl components demonstrably both antiparallel and with partial assignments of stereochemistry. Tetraethers with alternative arrangements of the components are absent. The structures allow previous observations on these and related lipids to be rationalized both biosynthetically and phyletically.     

Synthesis and chiroptical properties of neutral ether lipids

A variety of neutral ether lipids was synthesized. A method for the synthesis of 1,3-O-dialkyl-sn-glycerols was developed which involves selective alkylation of 3-O-alkyl-sn-glycerols. The ORD and CD curves of the various glyceryl ethers and their esters were analyzed. The correlation between the CD sign of the acyl residue and its position in the glycerol derivative was clarified.     

Evidence for Transaldolase Activity in the Isolated Heart Supplied with [U-13C3]Glycerol

Studies of glycerol metabolism in the heart have largely emphasized its role in triglyceride synthesis. However, glycerol may also be oxidized in the citric acid cycle, and glycogen synthesis from glycerol has been reported in the nonmammalian myocardium. The intent of this study was to test the hypothesis that glycerol may be metabolized to glycogen in mammalian heart. Isolated rat hearts were supplied with a mixture of substrates including glucose, lactate, pyruvate, octanoate, [U-¹³C₃]glycerol, and ²H₂O to probe various metabolic pathways including glycerol oxidation, glycolysis, the pentose phosphate pathway, and carbon sources of stored glycogen. NMR analysis confirmed that glycogen production from the level of the citric acid cycle did not occur and that the glycerol contribution to oxidation in the citric acid cycle was negligible in the presence of alternative substrates. Quite unexpectedly, ¹³C from [U-¹³C₃]glycerol appeared in glycogen in carbon positions 4–6 of glucosyl units but none in positions 1–3. The extent of [4,5,6-¹³C₃]glucosyl unit enrichment in glycogen was enhanced by insulin but decreased by H₂O₂. Given that triose phosphate isomerase is generally assumed to fully equilibrate carbon tracers in the triose pool, the marked ¹³C asymmetry in glycogen can only be attributed to conversion of [U-¹³C₃]glycerol to [U-¹³C₃]dihydroxyacetone phosphate and [U-¹³C₃]glyceraldehyde 3-phosphate followed by rearrangements in the nonoxidative branch of the pentose phosphate pathway involving transaldolase that places this ¹³C-enriched 3-carbon unit only in the bottom half of hexose phosphate molecules contributing to glycogen.     

Structural studies on santalin permethyl ether

The chloroform extract of the heartwood of Pterocarpus santalinus yielded a mixture of red pigments which could be separated by polyamide column chromatography into two major compounds, santalin-A and santalin-B. Both gave the same permethyl ether, C₃₈H₃₆O₁₀ which had 8 methoxyls and formed a number of derivatives typical of anhydrobenzopyranols. IR and UV spectra confirmed the same. NMR and MS suggested the presence of homoveratrayl group supported by the formation of veratraldehyde in alkali degradation. Permanganate oxidation gave 2,4-dimethoxy benzoic acid, veratric acid and 3,4,6-trimethoxy phthalic acid. On a basic fluorone skeleton, the substituents in the A ring are indicated by 2,4-dihydroxy-5-methoxy benzaldehyde, an alkali fission product and, further, 2,4-dimethoxy phenyl and homoveratryl units are located in ring C based on NMR, MS and biogenetic considerations. The residues constitute another benzene ring fused to ring C leading to the complete structures of the permethyl ether as (VII) which explains all its degradations and which constitutes a highly condensed biflavonoid of a new type.     

Oleaginous yeast Meyerozyma guilliermondii shows fermentative metabolism of sugars in the biosynthesis of ethanol and converts raw glycerol and cheese whey permeate into polyunsaturated fatty acids

We studied the biotechnological potential of the recently isolated yeast Meyerozyma guilliermondii BI281A to produce polyunsaturated fatty acids and ethanol, comparing products yields using glucose, raw glycerol from biodiesel synthesis, or whey permeate as substrates. The yeast metabolism was evaluated for different C/N ratios (100:1 and 50:1). Results found that M. guilliermondii BI281A was able to assimilate all tested substrates, and the most efficient conversion obtained was observed using raw glycerol as carbon source (C/N ratio 50:1), concerning biomass formation (5.67 g·L⁻¹) and lipid production (1.04 g·L⁻¹), representing 18% of dry cell weight. Bioreactors experiments under pH and aeration-controlled conditions were conducted. Obtained fatty acids were composed of ~67% of unsaturated fatty acids, distributed as palmitoleic acid (C_16:1, 9.4%), oleic acid (C_18:1, 47.2%), linoleic acid (C_{18:2 n−6}, 9.6%), and linolenic acid (C_{18:3 n−3}, 1.3%). Showing fermentative metabolism, which is unusual for oleaginous yeasts, M. guilliermondii produced 13.7 g·L⁻¹ of ethanol (yields of 0.27) when growing on glucose medium. These results suggest the promising use of this uncommonly studied yeast to produce unsaturated fatty acids and ethanol using cheap agro-industrial residues as substrates in bioprocess.     

Functional properties of diapophytoene and related desaturases of C30 and C40 carotenoid biosynthetic pathways

The desaturation reactions of C₃₀ carotenoids from diapophytoene to diaponeurosporene was investigated in vitro and by complementation in Escherichia coli. The expressed diapophytoene desaturase from Staphylococcus aureus inserts three double bonds in an FAD-dependent reaction. The enzyme is inhibited by diphenylamine. In the complementation experiment diapophytoene desaturase was able to convert C₄₀ phytoene to some extend but exhibited a high affinity to ζ-carotene. Comparison to the reaction of a phytoene desaturase from Rhodobacter capsulatus catalyzing a parallel three-step desaturation sequence with the corresponding C₄₀ carotenes revealed that this desaturase can also convert C₃₀ diapophytoene. Other homologous bacterial C₄₀ carotene desaturases could also utilize C₃₀ substrates, including one type of ζ-carotene desaturase which converted diaponeurosporene to diapolycopene. Further complementation experiments including the diapophytoene synthase gene from S. aureus revealed that the C₃₀ carotenogenic pathway is determined by this initial enzyme which is highly homologous to C₄₀ phytoene synthases.     

Chemical characterization of the lipophilic extract of Hydrilla verticillata: a widely spread aquatic weed

The composition of the lipophilic extract from Hydrilla verticillata, the common aquatic weed collected from Sasthamkotta Lake, the largest freshwater lake in Kerala, south of the west coast of India, was investigated. The lake is a designated wetland of international importance under the Ramsar Convention since 2002. GC-MS study of the unsaponifiable lipophilic extract of H. verticillata confirmed the presence of 3,5,11,15-tetramethyl 1- hexadecen-3-ol (C₂₀H₄₀O) and phytol (C₂₀H₄₀O) as major components, and their structures were elucidated. Phytol and 3,5,11,15-tetramethyl 1- hexadecen3-ol are the two isomers of the diterpeneol (C₂₀H₄₀O) found in the unsaponifible lipophilic extract of H. verticillata and are formed by the hydrolysis of the alcohol moiety of chlorophyll. On quantification, an appreciable concentration of phytol (6.39 g?Kg^?1) was estimated. The feasibility to utilize H. verticillata to produce phytol is to be addressed by further studies since H. verticillata is considered as one of the world’s fast widely spread aquatic weeds on account of its numerous mechanisms of vegetative reproductions.     

Biohydrogenation of C20 polyunsaturated fatty acids by anaerobic bacteria

The PUFAs include many bioactive lipids. The microbial metabolism of C₁₈ PUFAs is known to produce their bioactive isomers, such as conjugated FAs and hydroxy FAs, but there is little information on that of C₂₀ PUFAs. In this study, we aimed to obtain anaerobic bacteria with the ability to produce novel PUFAs from C₂₀ PUFAs. Through the screening of ∼100 strains of anaerobic bacteria, Clostridium bifermentans JCM 1386 was selected as a strain with the ability to saturate PUFAs during anaerobic cultivation. This strain converted arachidonic acid (cis-5,cis-8,cis-11,cis-14-eicosatetraenoic acid) and EPA (cis-5,cis-8,cis-11,cis-14,cis-17-EPA) into cis-5,cis-8,trans-13-eicosatrienoic acid and cis-5,cis-8,trans-13,cis-17-eicosatetraenoic acid, giving yields of 57% and 67% against the added PUFAs, respectively. This is the first report of the isolation of a bacterium transforming C₂₀ PUFAs into corresponding non-methylene-interrupted FAs. We further investigated the substrate specificity of the biohydrogenation by this strain and revealed that it can convert two cis double bonds at the ω6 and ω9 positions in various C₁₈ and C₂₀ PUFAs into a trans double bond at the ω7 position. This study should serve to open up the development of novel potentially bioactive PUFAs.     

Electrochemical changes in media due to microbial

Microbial metabolism affected the electrical impedance parameters of a two terminal-measuring cell-containing growth media. The relationship between microbial growth and relative changes in both The capacitive and resistive parts of impedance was examined. Both components of impedance were shown to be indicative of bacterial growth. In low conductivity media the change in the conductance of the media (G_sol) clearly correlated to bacterial growth. In more conductive media the relative changes in G_sol were smaller, and in these media measurements of the changes of polarization capacitance (C_pol) were useful for monitoring bacterial growth.Yeast growth in two media resulted in large changes in C_pol (20–100%) while the changes in G_sol were very small (1–4%). This result indicated that, for some combinations of microorganisms and media, measuring C_pol might be preferable over G_sol for the detection of microbial growth.Microbial metabolism resulted in a change of 2–2.5 units in pH. This pH change resulted in a 40% change in C_pol but less than a 14% change in G_sol.     

Synthesis and cytotoxicity of novel phosphorusless analogues of edelfosine

Modified series of phosphorusless edelfosine analogues bearing the polar heads of aliphatic bases, N,N-dimethylethanolamine and N,N,N1,N¹-tetramethylethylenediamine, were synthesized, with the length of the spacer varying from three to four methylene units. The cytotoxic characteristics of the compounds synthesized were studied.     

Monolayers of ether lipids from archaebacteria

The surface behavior of six different ether lipids from archaebacteria, based on condensation of glycerol or more complex polyols with two isoprenoid alcohols at 20 or 40 carbon atoms, was investigated in monolayers at the air-water interface.The compounds with no complex polar group (GD, GDGT, GDNT) form monolayers showing a reversible collapse at surface pressure as low as 22 dynes/cm. This collapse pressure decrease with temperature in such a way that the film tension remains constant. In condensed films, these molecules do not assume a completely upright position.Lipids with complex polar ends (HL, GLB, PLII) form films more stable to compression. Forcearea characteristics and surface moment values of HL monolayers are similar to those of analogous ester lipids with fatty acid chains. Monolayers of the two bipolar lipids, GLB and PLII, at room temperature present a more condensed state, probably due to the lateral cohesion between long alkyl chains, but a lower collapse pressure.For all bipolar lipids, the area expansion induced by temperature increase is larger than that of monopolar ones.Abbreviations GD Glycerol diether (2,3-di-O-phytanyl-sn-glycerol - GDGT Glycerol-dialkyl-glycerol tetraether - GDNT Glycerol-dialkyl-nonitol tetraether - GLB Glycolipid B - PLII Phospholipid II - HL Total lipid extract from Halobacterium halobium     

Metabolite regulation of partially purified soybean nodule phosphoenolpyruvate carboxylase

Phosphoenolpyruvate carboxylase (PEPC) was purified 40-fold from soybean (Glycine max L. Merr.) nodules to a specific activity of 5.2 units per milligram per protein and an estimated purity of 28%. Native and subunit molecular masses were determined to be 440 and 100 kilodaltons, respectively, indicating that the enzyme is a homotetramer. The response of enzyme activity to phosphoenolpyruvate (PEP) concentration and to various effectors was influenced by assay pH and glycerol addition to the assay. At pH 7 in the absence of glycerol, the K_m (PEP) was about twofold greater than at pH 7 in the presence of glycerol or at pH 8. At pH 7 or pH 8 the K_m (MgPEP) was found to be significantly lower than the respective K_m (PEP) values. Glucose-6-phosphate, fructose-6-phosphate, glucose-1-phosphate, and dihydroxyacetone phosphate activated PEPC at pH 7 in the absence of glycerol, but had no effect under the other assay conditions. Malate, aspartate, glutamate, citrate, and 2-oxoglutarate were potent inhibitors of PEPC at pH 7 in the absence of glycerol, but their effectiveness was decreased by raising the pH to 8 and/or by adding glycerol. In contrast, 3-phosphoglycerate and 2-phosphoglycerate were less effective inhibitors at pH 7 in the absence of glycerol than under the other assay conditions. Inorganic phosphate (up to 20 millimolar) was an activator at pH 7 in the absence of glycerol but an inhibitor under the other assay conditions. The possible significance of metabolite regulation of PEPC is discussed in relation to the proposed functions of this enzyme in legume nodule metabolism.     

Composition of leaf epicuticular waxes of Pteridium subspecies

The leaf epicuticular waxes of two subspecies of Pteridium consisted principally of alkyl esters (92 %; C₄₀–C₅₀) together with small amounts of n-alkanols (2 %; C₂₄–C₃₂) and hydrocarbons (2%; C₂₇–C₃₁). The esters comprised C₂₂–C₃₂ alkanols randomly combined with C₂₀ – C₂₄ fatty acids.