An integrated procedure for the extraction of bacterial isoprenoid quinones and polar lipids

A simple small-scale procedure for the sequential extraction of isoprenoid quinones and polar lipids from bacterial cells was developed. Extraction with a biphasic mixture of petroleum ether (b.p. 60–80°C) and methanolic saline gave an upper phase containing isoprenoid quinones. The lower phase, containing the partially extracted organisms, was processed according to the Bligh and Dyer extraction method to give a polar lipid extract. As examples of the procedure, the isoprenoid quinones and polar lipids of Bacillus subtilis, Mycobacterium avium, Pseudomonas diminuta and Streptomyces griseus were extracted and analyzed.     

Liquid membrane extraction of bio-active amphiphilic substances: Recovery of surfactin

The interest of application of liquid membrane (pertraction) processes for recovery of biosurfactants from aqueous media was demonstrated. Transport of pure surfactin in three-liquid-phase system was studied. Surfactin was successfully extracted from slightly acid media (pH 5.65–6.05) applying batch pertraction in a rotating discs contactor and using n-heptane as liquid membrane. The process efficiency was found to be strongly affected by the feed solution acidity (83% at pH_F 6.05 and 97% at pH_F 5.65 after 4 h pertraction).An atypical pH effect was observed when the behaviour of surfactin extraction from aqueous media by non-polar solvents (n-heptane and n-octane) was studied. The obtained high extraction degrees from both acid and basic media and the clearly reduced degree of extraction from neutral media could be attributed to the different conformations of surfactin in these media.     

Effects of oxygen vectors on the synthesis and molecular weight of poly(γ-glutamic acid) and the metabolic characterization of Bacillus subtilis NX-2

The effects of different oxygen vectors on the synthesis and molecular weight of poly(γ-glutamic acid) (PGA) were investigated in the batch fermentation of Bacillus subtilis NX-2. n-Hexane, n-heptane, and n-hexadecane enhanced the PGA concentration and molecular weight. The PGA concentration reached a maximum of 39.4 ± 0.19 g L^?1, and the highest molecular weight obtained was (19.0 ± 0.02) × 10⁵ Da with the addition of 0.3% n-heptane. However, n-dodecane decreased the PGA concentration and molecular weight to final values of 20.1 ± 0.10 g L^?1 and (8.4 ± 0.02) × 10⁵ Da, respectively. Analysis of the intracellular nucleotide levels of B. subtilis NX-2 with n-heptane and n-dodecane additives showed that the lowest NADH/NAD⁺ ratio and ATP levels were obtained with the n-dodecane additives, which can explain the decreased PGA yield and molecular weight. The metabolic flux distribution of B. subtilis NX-2 with n-heptane and n-dodecane additives was also investigated. Flux distribution was primarily directed to the EMP and TCA cycles with n-heptane additives. The flux of 2-oxoglutarate to intracellular glutamate and the flux distribution from extracellular to intracellular glutamate both increased to improve PGA production.     

On the role of electron impact in an atmospheric-pressure microwave discharge in liquid <Emphasis Type="Italic">n</Emphasis>-heptane

The role of electron impact in the dissociation of n-heptane in an atmospheric-pressure microwave discharge in liquid n-heptane was investigated using a self-consistent two-dimensional model. The model includes the Navier–Stokes equations for a two-phase subsonic flow of incompressible liquid and compressible gas, the heat conduction equation, Maxwell’s equations for the microwave field, the Boltzmann equation for plasma electrons, and the balance equations for the electron density and weight fraction of n-heptane in the gaseous and liquid phases. It is shown that the effect of electron impact is negligible at times longer than 10^–3 s.     

Biosurfactants production by immobilized cells of Bacillus subtilis ATCC 21332 and their recovery by pertraction

Microbial production and isolation of biosurfactants was studied. The production of lipopeptides surfactin and fengycin was performed by free and immobilized aerobic cells of Bacillus subtilis ATCC 21332. After preliminary tests with 5 polymer materials, the particles of polypropylene foamed with powder activated carbon (PPch) were selected for lipopeptides production for their thermal and mechanical stability and for the high colonizing effect. To avoid foaming during biosurfactant production, biofilm grown on solid floating support was aerated by air injected over the surface of cultural medium. The synthesis of both lipopeptides and especially of the fengycin was greatly enhanced by the immobilization. The relationship between support wettability, colonization of the cells, and lipopeptide production was discussed. Extraction behaviour of the lipopeptides into alkanes was studied. The distribution ratio of surfactin was found to be higher than this of fengycin at the same conditions and the n-heptane was more efficient solvent for both lipopeptides. Kinetics of surfactin recovery from fermentation broth applying batch pertraction in a rotating discs contactor was studied. Lipopeptide was successfully extracted (more than 75% in the first hour) using n-heptane as liquid membrane and a 0.2 mol L⁻¹ phosphate buffer solution (pH ∼ 7.3) as receiving solution. However, the stripping of the organic liquid and surfactin accumulation into the receiving phase were less efficient.     

Pressurized solvent extraction of pure food grade starch

A commercial pressurized solvent extractor was used to remove lipid and non-lipid material from cornstarch using n-propanol/water and ethanol/water mixtures. Yields and chemical composition of the extract fractions were determined. Cornstarch samples were characterized using pasting properties and shear storage modulus measurements. The n-propanol/water extracted slightly higher amounts of both lipids and non-lipids. The lipid fractions contained mostly linoleic, palmitic and oleic free fatty acids. The non-lipid fraction contained mostly protein in the form of zein. The extracted starch had lower peak and setback viscosities than did the unextracted starch. The starch extracted with n-propanol/water had the lowest shear storage modulus values. Conversely, the samples extracted with ethanol/water had the highest shear storage modulus values. It is hypothesized that low amounts of zein present in conjunction with the starch is responsible for this observed effect.     

Carbon and hydrogen isotopic fractionation during lipid biosynthesis in a higher plant (Cryptomeria japonica)

Compound-specific carbon and hydrogen isotopic compositions of lipid biomolecules (n-alkanes, n-alkanoic acids, n-alkanols, sesquiterpenes, diterpenes, phytol, diterpenols and β-sitosterol), extracted from Cryptomeria japonica leaves, were determined in order to understand isotopic fractionations occurring during lipid biosynthesis in this species. All lipid biomolecules were depleted in both ¹³C and D relative to bulk tissue and ambient water, respectively. n-Alkyl lipids associated with the acetogenic pathway were depleted in ¹³C relative to bulk tissue by 2.4-9.9‰ and depleted in D relative to ambient water by 91-152‰. C₁₅- and C₃₀-isoprenoid lipids (sesquiterpenes, squalene and β-sitosterol) associated with the mevalonic-acid pathway are depleted in ¹³C relative to bulk tissue by 1.7-3.1‰ and depleted in D relative to ambient water by 212-238‰. C₂₀-isoprenoid lipids (phytol and diterpenoids) associated with the non-mevalonic-acid pathway were depleted in ¹³C relative to bulk tissue by 4.6-5.9‰ and depleted in D relative to ambient water by 238-303‰. Phytol was significantly depleted in D by amounts up to 65‰ relative to other C₂₀ isoprenoid lipids. The acetogenic, mevalonic-acid and non-mevalonic-acid pathways were clearly discriminated using a cross-plot between the carbon and hydrogen isotopic fractionations.     

Paraffin Oxidation in Pseudomonas aeruginosa II. Gross Fractionation of the Enzyme System into Soluble and Particulate Components

Osmoplast production in Pseudomonas aeruginosa was investigated to obtain osmotically sensitive cells for studies on the subcellular location of the paraffin-oxidizing enzyme system. It proved possible to convert cells of P. aeruginosa treated with lysozyme and ethylenediaminetetraacetic acid in tris(hydroxymethyl)aminomethane-sucrose buffer (pH 8) into osmotically sensitive cells within 2 min. Active, cell-free preparations were obtained by the subsequent osmotic disruption in the presence of deoxyribonuclease and magnesium chloride. The conditions necessary for a complete separation of membranes and soluble cell constituents were established by following the distribution of two reference enzymes. An enzyme assay based on direct gas chromatographic analysis of the oxidation products from n-heptane is described for the paraffin-oxidizing enzyme system. By using this method, we investigated the enzymatic organization and subcellular distribution of the paraffin-oxidizing enzyme system. It was confirmed that the enzyme system is composed of three components, each of which is indispensable for the hydroxylation of n-heptane. One of these components, the hydroxylase, was located in two cell fractions; the other two components occur exclusively in the soluble cell fraction. The half-life of a crude enzyme preparation kept at ambient temperature is approximately 3.5 hr. This poor stability was found to be primarily due to the instability of one of the soluble factors, presumably the reduced nicotinamide adenine dinucleotide-rubredoxin reductase.     

Dietary Omega-3 Polyunsaturated Fatty Acids Alter the Fatty Acid Composition of Hepatic and Plasma Bioactive Lipids in C57BL/6 Mice: A Lipidomic Approach

Background

Omega (n)-3 polyunsaturated fatty acids (PUFA) are converted to bioactive lipid components that are important mediators in metabolic and physiological pathways; however, which bioactive compounds are metabolically active, and their mechanisms of action are still not clear. We investigated using lipidomic techniques, the effects of diets high in n-3 PUFA on the fatty acid composition of various bioactive lipids in plasma and liver.

Methodology and Principal Findings

Female C57BL/6 mice were fed semi-purified diets (20% w/w fat) containing varying amounts of n-3 PUFA before mating, during gestation and lactation, and until weaning. Male offspring were continued on their mothers’ diets for 16 weeks. Hepatic and plasma lipids were extracted in the presence of non-naturally occurring internal standards, and tandem electrospray ionization mass spectrometry methods were used to measure the fatty acyl compositions. There was no significant difference in total concentrations of phospholipids in both groups. However, there was a significantly higher concentration of eicosapentaenoic acid containing phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and cholesteryl esters (CE) (p < 0.01) in the high n-3 PUFA group compared to the low n-3 PUFA group in both liver and plasma. Plasma and liver from the high n-3 PUFA group also had a higher concentration of free n-3 PUFA (p < 0.05). There were no significant differences in plasma concentrations of different fatty acyl species of phosphatidylethanolamine, triglycerides, sphingomyelin and ceramides.

Conclusions/Significance

Our findings reveal for the first time that a diet high in n-3 PUFA caused enrichment of n-3 PUFA in PC, LPC, CE and free fatty acids in the plasma and liver of C57BL/6 mice. PC, LPC, and unesterified free n-3 PUFA are important bioactive lipids, thus altering their fatty acyl composition will have important metabolic and physiological roles.     

Effects of Q metabolites and related compounds on mitochondrial succinate and NADH oxidase systems

The effects of Q metabolites (Q acid-I, Q acid-II) and related compounds (dihydro Q acid-I, dehydro Q acid-II, QS-n, and their esters) on mitochondrial succinate and NADH oxidase systems were investigated. The activity restoring succinate oxidation in acetone-treated beef heart mitochondria was found to decrease with descending order of carbon number (n) of the side chain of the Q metabolites; activity was restored with Q acid-I (n = 7) to one-third as much as that with Q-7 and Q-10, but Q acid-II (n = 5) did not restore any activity. Of the related compounds with a carboxyalkyl group (QS-n), QS-16-QS-18 (n = 16–18) were found to be most active, and their activities were also correlated with n. The relationship between the restoration of activity and the partition coefficient was considered. NADH oxidation in pentane-treated beef heart submitochondrial particles could be restored with esters of low molecular weight quinones to the same extent as with Q-10, but not with the metabolites.     

Synthesis of 4-nitrophenyl acetate using molecular sieve-immobilized lipase from <Emphasis Type="Italic">Bacillus coagulans</Emphasis>

Extracellular lipase from Bacillus coagulans BTS-3 was immobilized on (3 Å × 1.5 mm) molecular sieve. The molecular sieve showed approximately 68.48% binding efficiency for lipase (specific activity 55 IU mg^?1). The immobilized enzyme achieved approx 90% conversion of acetic acid and 4-nitrophenol (100 mM each) into 4-nitrophenyl acetate in n-heptane at 65°C in 3 h. When alkane of C-chain length other than n-heptane was used as the organic solvent, the conversion of 4-nitrophenol and acetic acid was found to decrease. About 88.6% conversion of the reactants into ester was achieved when reactants were used at molar ratio of 1:1. The immobilized lipase brought about conversion of approximately 58% for esterification of 4-nitrophenol and acetic acid into 4-nitrophenyl acetate at a temperature of 65°C after reuse for 5 cycles.     

The desaturation and elongation of linolenic acid and eicosapentaenoic acid by hepatocytes and liver microsomes from rainbow trout (Oncorhynchus mykiss) fed diets containing fish oil or olive oil

The products of desaturation and elongation of [1−¹⁴C] 18:3(n − 3) and [1−¹⁴C]20:5(n − 3) were studied using hepatocytes and microsomes prepared from livers of trout maintained on diets containing either olive oil or fish oil, to establish the extent to which the formation of 22:6(n − 3) was enhanced in the absence of dietary 22:6(n − 3) and to investigate the pathway(s) of conversion of 18:3(n − 3) and 20:5(n − 3) to 22:6(n − 3). Levels of 20:5(n − 3) and 22:6(n − 3) in the total lipid of hepatocytes from trout fed olive oil were 20-fold and 10-fold, respectively, lower than in cells from trout fed fish oil. For both dietary groups, [1−¹⁴C]18:3(n − 3) was incorporated into hepatocyte lipid to a greater extent than [1−¹⁴C]20:5(n − 3). Almost 70% of the total radioactivity from [1−¹⁴C]18:3(n − 3) was recovered in hepatocyte triacylglycerols, whereas radioactivity from [1−¹⁴C]20:5(n − 3) was recovered almost equally in neutral lipids (52%) and polar lipids (48%). The products of desaturation and elongation from both labelled substrates were esterified mainly into hepatocyte polar lipids, whereas elongation products of [1−¹⁴C]18:3(n − 3) were preferentially incorporated into neutral lipids. Radioactivity recovered in the 22:6(n − 3) of polar lipids of hepatocytes from trout fed olive oil, from both ¹⁴C substrates, was approximately double that in hepatocytes from trout fed fish oil. No radioactivity from either [1−¹⁴C]18:3(n − 3) or [1−¹⁴C]20:5(n − 3) was incorporated into 22:6(n − 3) by microsomes isolated from livers from either group of fish and incubated in the presence of acetyl-CoA, malonyl-CoA, NADH, NADPH, ATP and coenzyme A. However, significant radioactivity was recovered in 24:5(n − 3) and 24:6(n − 3) from [1−¹⁴C]20:5(n − 3) and more radioactive 24:6(n − 3) accumulated in microsomes from trout fed olive oil than from trout fed fish oil. The results establish that the formation of 22:6(n − 3) from both 18:3(n − 3) and 20:5(n − 3) in hepatocytes of rainbow trout is stimulated by omitting 22:6(n − 3) from the diet and are consistent with the biosynthesis of 22:6(n − 3) in trout liver cells proceeding via 24:5(n − 3) and 24:6(n − 3) intermediates.     

Antiplasmodial activity of quinones: Roles of aziridinyl substituents and the inhibition of Plasmodium falciparum glutathione reductase

Although quinones have been the subject of great interest as possible antimalarial agents, the mechanism of their antimalarial activity is poorly understood. Flavoenzyme electrontransferase-catalyzed redox cycling of quinones, and their inhibition of the antioxidant flavoenzyme glutathione reductase (GR, EC 1.8.1.7) have been proposed as possible mechanisms. Here, we have examined the activity of a number of quinones, including the novel antitumor agent RH1, against the malaria parasite Plasmodium falciparum strain FcB1 in vitro, their single-electron reduction rates by P. falciparum ferredoxin:NADP⁺ reductase (PfFNR, EC 1.18.1.2), and their ability to inhibit P. falciparum GR. The multiparameter statistical analysis of our data implies, that the antiplasmodial activity of fully-substituted quinones (n = 15) is relatively independent from their one-electron reduction potential (). The presence of aziridinyl groups in quinone ring increased their antiplasmodial activity. Since aziridinyl-substituted quinones do not possess enhanced redox cycling activity towards PfFNR, we propose that they could act as as DNA-alkylating agents after their net two-electron reduction into aziridinyl-hydroquinones. We found that under the partial anaerobiosis, i.e., at the oxygen concentration below 40-50 μM, this reaction may be carried out by single-electron transferring flavoenzymes present in P. falciparum, like PfFNR. Another parameter increasing the antiplasmodial activity of fully-substituted quinones is an increase in their potency as P. falciparum GR inhibitors, which was revealed using multiparameter regression analysis. To our knowledge, this is the first quantitative demonstration of a link between the antiplasmodial activity of compounds and GR inhibition.     

Photosystem II Core Phosphorylation Heterogeneity, Differential Herbicide Binding, and Regulation of Electron Transfer in Photosystem II Preparations from Spinach

The effect of photosystem II core phosphorylation on the secondary quinone acceptor of photosystem II (Q_B) domain environment was analyzed by comparative herbicide-binding studies with photosystem II preparations from spinach (Spinacia oleracea L.). It was found that phosphorylation reduces the binding affinity for most photosynthetic herbicides. The binding of synthetic quinones and of the electron acceptor 2,6-dichlorophenolindophenol is also reduced by photosystem II phosphorylation. Four photosystem II core populations isolated from membranes showed different extents of phosphorylation as well as different degrees of affinity for photosynthetic herbicides. These findings support the idea that heterogeneity of photosystem II observed in vivo could be, in part, due to phosphorylation.     

Maintenance of lower proportions of (n − 6) eicosanoid precursors in phospholipids of human plasma in response to added dietary (n − 3) fatty acids

Competition between the (n ? 3) and (n ? 6) types of highly unsaturated fatty acids can diminish the abundance of (n ? 6) eicosanoid precursors in a tissue, which in turn can diminish the intensity of tissue responses that are mediated by (n ? 6) eicosanoids. The mixture of 20- and 22-carbon highly unsaturated fatty acids maintained in the phospholipids of human plasma is related to the dietary intake of 18:2 (n ? 6) and 18:3 (n ?3) by empirical hyperbolic equations in a manner very similar to the relationship reported for laboratory rats (Lands, W.E.M., Morris, A. and Libelt, B. (1990) Lipids 25, 505–516). Analytical results from volunteers ingesting self-selected diets showed an inter-individual variance for the proportion of (n ? 6) eicosanoid precursors in the fatty acids of plasma phospholipids of about 5%, but the variance among multiple samples taken from the same individual throughout the day was less (about 3%), closer to the experimental variance of the analytical procedure (about 1%). The reproducibility of the results makes it likely that analysis of fatty-acid composition of plasma lipids from individuals will prove useful in estimating the diet-related tendency for severe thrombotic, arthritic of other disorders that are mediated by (n ? 6) eicosanoids. Additional constants and terms were included in the equations to account for the effects of 20- and 22-carbon highly unsaturated (n ? 3) fatty acids in the diet. A lower constant for the 20- and 22-carbon (n ? 3) fatty acids compared to that for the 18-carbon (n ? 3) fatty acid in decreasing the ability of dietary 18:2 (n ? 6) to maintain 20:4 (n ? 6) in tissue lipids confirmed the greater competitive effectiveness of the more highly unsaturated n ? 3 fatty acids in the elongation/ desaturation process. Also, a lower constant for direct incorporation of 20-carbon fatty acids of the n ? 6 vs. the n ? 3 type indicated a greater competitive effectiveness of 20:4 (n ? 6) relative to 20:5 (n ? 3) in reesterification after release from tissue lipids. The equations may be used in reverse to estimate the dietary intakes of the (n ? 3) and (n ? 6) fatty acids by using the composition of the fatty acids that had been maintained in plasma lipids.     

Effect of Pt and Sn on the adsorption of n-heptane in γ-Al2O3 catalyst models

The Grand Canonical Monte-Carlo (GCMC) method has been used to carry out simulations of the adsorption of n-heptane in models of naphtha-reforming catalysts. Models used in the study differed in the number and distribution of metal atoms—Pt and Sn. The number of adsorbed n-heptane molecules grows linearly with increasing number of metal atoms. The effect of Pt content on the adsorption of n-heptane molecules is most distinct at approximately 100 kPa and within the lower range of the temperatures investigated. In the models of bimetallic catalysts, the effect of the two metals is additive.Figure Effect of Pt and Sn on number of n-heptane molecules adsorbed in Al₂O₃ catalyst in 773 K and 1000 kPa.      

Lipase immobilized microstructured fiber based flow-through microreactor for facile lipid transformations

A facile continuous flow-through Candida antarctica lipase B immobilized silica microstructured optical fiber (SMOF) microreactor for application in lipid transformations has been demonstrated herewith. The lipase was immobilized on the amino activated silica fiber using glutaraldehyde as a bifunctional reagent. The immobilized lipase activity in the SMOF was tested calorimetrically by determination of p-nitrophenyl butyrate hydrolysis products. The specific activity of the immobilized lipase was calculated to be 0.91 U/mg. The SMOF microreactor performance was evaluated by using it as a platform for synthesis of butyl laurate from lauric acid and n-butanol in n-hexane and n-heptane at 50 °C, with products identified by gas chromatography–mass spectrometry (GC–MS). Different substrate mole ratios were evaluated, with 1:3, lauric acid:n-butanol showing best performance. Remarkably, percentage yields of up to 99% were realized with less than ∼38 s microreactor residence time. In addition, the SMOF microreactor could be reused many times (at least 7 runs) with minimal reduction in the activity of the enzyme. The enzyme stability did not change even with storage of the microreactor in ambient conditions over one month.     

The composition of cuticular hydrocarbons of the khapra beetles,trogoderma granarium

• 1.1. The cuticular and internal hydrocarbons of the khapra beetle Trogoderma granarium were studied by capillary column gas chromatography and mass spectrometry. n-Alkanes, 3-methyl-, 5-methyl-, 11-methyl-, 12-methyl-, 13-methyl-, 14-methyl- and 15-methylalkanes were found in the cuticular and internal lipids.
• 2.2. Some quantitative differences of the compositions were estimated for cuticular and internal hydrocarbons.
• 3.3. The n-alkanes in the samples are mostly odd chain lengths from 23 to 33 carbon atoms. In turn, the branched hydrocarbons consist of even carbon numbers ranging from C₂₆ to C₃₂, but the branching points are situated on the odd carbon numbers.
• 4.4. There are similarities in the n-alkanes patterns extracted from khapra beetle and wheat grains, the latter of which are the natural nutrition of this pest.

     

Isoprenoid quinones in an aerobic hyperthermophilic archaeon, Aeropyrum pernix

Aeropyrum pernix is the first strictly aerobic hyperthermophile known to grow heterotrophically at neutral pH and at temperatures up to 100°C. Using a simple and sensitive frit-fast atom bombardment liquid chromatography/mass spectrometry quinone analysis method, we analyzed the quinones in A. pernix. This organism contained demethylmenaquinone analogs (DMK-6(H_n)) and methionaquinone analogs (MTK-6(H_n)) when it was grown under vigorous shaking in the presence of air. The quinones were partially or fully saturated with six isoprenyl units. Although DMK and MTK are the quinones found in eubacteria, this is the first report to demonstrate the simultaneous occurrence of DMK and MTK in archaea. The effect of Na₂S₂O₃ on the quinone composition was studied at concentrations of 0, 0.1 and 0.5% under aerobic growth conditions with shaking. The total quinone content was highest (83.4 μg g⁻¹ dry cell weight) at 0.1% Na₂S₂O₃. In the absence of Na₂S₂O₃, only DMK-6 analogs were detected. While DMK analogs such as DMK-6(H₁₂), DMK-6(H₁₀) and DMK-6(H₈) were the major quinones at 0.1% Na₂S₂O₃, MTK analogs such as MTK-6(H₁₂) and MTK-6(H₁₀) were also detected. When the Na₂S₂O₃ concentration was increased to 0.5%, both DMK-6(H₈) and MTK-6(H₁₀) disappeared, while MTK-6(H₁₂) increased to approximately 20% of the total quinone content. When A. pernix was grown under oxygen limitation in a tightly closed bottle without gas phase, MK-6(H₁₀) appeared.     

Lipids of chill-sensitive and -resistant Passiflora species: Fatty acid composition and temperature dependence of spin label motion

Polar lipids were extracted from the leaves of Passiflora species which varied in their resistance to chilling injury. The fatty acid compositions of the 8 major polar lipid classes from P. caerulea (chill-resistant) were generally similar to those of the corresponding lipids from P. flavicarpa (chill-sensitive). Using ESR spectroscopy, the motion of spin-labelled molecules was measured in phospholipids isolated from a range of Passiflora species. The temperature dependence of the motion of the spin labels showed a change at 1° for lipids of the most chill-resistant species and at 9° for the lipids of the most chill-sensitive species. Lipids from other species showed changes at intermediate temperatures, and the greater the chilling sensitivity of the species, the higher was the temperature of the change. It is concluded that pronounced differences in chilling sensitivity of the Passiflora species are correlated with physical differences in their membrane lipids; however, the degree of unsaturation of the lipids is not a reliable guide to chilling sensitivity.