Fatty acid constituents of Peganum harmala plant using Gas Chromatography–Mass Spectroscopy

Fatty acid contents of the Peganum harmala plant as a result of hexane extraction were analyzed using GC–MS. The saturated fatty acid composition of the harmal plant was tetradecanoic, pentadecanoic, tridecanoic, hexadecanoic, heptadecanoic and octadecanoic acids, while the saturated fatty acid derivatives were 12-methyl tetradecanoic, 5,9,13-trimethyl tetradecanoic and 2-methyl octadecanoic acids. The most abundant fatty acid was hexadecanoic with concentration 48.13% followed by octadecanoic with concentration 13.80%. There are four unsaturated fatty acids called (E)-9-dodecenoic, (Z)-9-hexadecenoic, (Z,Z)-9,12-octadecadienoic and (Z,Z,Z)-9,12,15-octadecatrienoic. The most abundant unsaturated fatty acid was (Z,Z,Z)-9,12,15-octadecatrienoic with concentration 14.79% followed by (Z,Z)-9,12-octadecadienoic with concentration 10.61%. Also, there are eight non-fatty acid compounds 1-octadecene, 6,10,14-trimethyl-2-pentadecanone, (E)-15-heptadecenal, oxacyclohexadecan-2 one, 1,2,2,6,8-pentamethyl-7-oxabicyclo[4.3.1]dec-8-en-10-one, hexadecane-1,2-diol, n-heneicosane and eicosan-3-ol.     

In vivo biosynthesis of -linolenic acid in plants

[1-¹⁴C]acetate was readily incorporated into unsaturated fatty acids by leaf slices of spinach, barley and whole cells of $\text{Chlorella}\text{pyrenoidosa}$ and $\text{Candida}\text{bogoriensis}$. In these systems the [¹⁴C] label in newly synthesized oleate and linoleate was approximately equally distributed in the C_1–9 and the C_10–18 fragments obtained by reductive ozonolysis of these acids, whereas in a-linolenic acid over 90% of the total [¹⁴C] was localized in the C_1–9 fragment. While [1-¹⁴C]oleic acid was converted by whole cells of $\text{Chlorella}$ to [1-¹⁴C]linoleic and [1-¹⁴C]linolenic acids, [U-¹⁴C]oleic acid yielded [U-¹⁴C]linoleic acid but a-linolenic acid was labeled only in the carboxyl terminal carbon atoms. When spinach leaf slices were supplied with carboxyl labeled octanoic, decanoic, dodecanoic, tetradecanoic and octadecanoic acids, only the first three acids were converted to a-linolenic acids while the last two acids were ineffective. Thus we suggest that (a) linoleic acid is not the precursor of a-linolenic acid and (b) 12:3(3, 6, 9) is the earliest permissible trienoic acid which is then elongated to a-linolenic acid.     

The influence of charge on phosphatidic acid bilayer membranes

A complete titration of phosphatidic acid bilayer membranes was possible for the first time by the introduction of a new anaologue, $\text{1,2-}\text{dihexadecyl}\text{-sn-}\text{glycerol-3-phosphoric}$ acid, which has the advantage of a high chemical stability at extreme pH values. The synthesis of this phosphatidic acid is described and the phase transition behaviour in aqueous dispersions is compared with that of three ester phosphatidic acids; $\text{1,2-}\text{dimyristoyl}\text{-sn-}\text{glycerol-3-phosphoric}$ acid, 1,3-dimyristoylglycerol-2-phosphoric acid and $\text{1,2-}\text{dipalmitoyl}\text{-sn-}\text{glycerol-3-phosphoric}$ acid.The phase transition temperatures ($\text{T}{}_{\mathrm{<mtext>t</mtext>}}$) of aqueous phosphatidic acid dispersions at different degrees of dissociation were measured using fluorescence spectroscopy and 90° light scattering. The $\text{T}{}_{\mathrm{<mtext>t</mtext>}}$ values are comparable to the melting points of the solid phosphatidic acids in the fully protonated states, but large differences exist for the charged states.The $\text{T}{}_{\mathrm{<mtext>t</mtext>}}$ vs. pH diagrams of the four phosphatidic acids are quite similar and of a characteristic shape. Increasing ionisation results in a maximum value for the transition temperatures at pH 3.5 ($\text{p}\text{K}{}_1$). The regions between the first and the second $\text{p}\text{K}$ of the phosphatidic acids are characterised by only small variations in the transition temperatures (extended plateau) in spite of the large changes occurring in the surface charge of the membranes. The slope of the plateau is very shallow with increasing ionisation. A further decrease in the H⁺ concentration results in an abrupt change of the transition temperature. The slope of the $\text{T}{}_{\mathrm{<mtext>t</mtext>}}$ vs. pH diagram beyond $\text{p}\text{K}{}_2$ becomes very steep. This is the     

Characterisation of two self-sufficient CYP102 family monooxygenases from Ktedonobacter racemifer DSM44963 which have new fatty acid alcohol product profiles

BackgroundTwo self-sufficient CYP102 family encoding genes (Krac_0936 and Krac_9955) from the bacterium Ktedonobacter racemifer DSM44963, which possesses one of the largest bacterial genomes, have been identified.MethodsPhylogenetic analysis of both the encoded cytochrome P450 enzymes, Krac0936 and Krac9955. Both enzymes were produced and their turnovers with fatty acid substrates assessed in vitro and using a whole-cell oxidation system.ResultsKrac0936 hydroxylated straight chain, saturated fatty acids predominantly at the ω-1 and ω-2 positions using NADPH as the cofactor. Krac0936 was less active towards shorter unsaturated fatty acids but longer unsaturated acids were efficiently oxidised. cis,cis-9,12-Octadecadienoic and pentadecanoic acids were the most active substrates tested with Krac0936. Unusually Krac9955 showed very low levels of NAD(P)H oxidation activity though coupling of the reducing equivalents to product formation was high. The product distribution of tridecanoic, tetradecanoic and pentadecanoic acid oxidation by Krac9955 favoured oxidation at the ω-4, ω-5 and ω-6 positions, respectively.ConclusionKrac0936 and Krac9955 are self-sufficient P450 monooxygenases. Krac0936 has a preference for pentadecanoic acid over other straight chain fatty acids and showed little or no activity with dodecanoic or octadecanoic acids. Krac9955 preferably oxidised shorter fatty acids compared to Krac0936 with tridecanoic having the highest levels of product formation. Unlike Krac0936 and P450Bm3, Krac9995 showed lower activities with unsaturated fatty acids.General significanceIn this study of two of the CYP enzymes from K. racemifer we have shown that this bacterium from the Chloroflexi phylum contains genes which encode new proteins with novel activity.     

Synomones in necrophagous larvae of the blow flies Lucilia sericata and Calliphora vomitoria

Chemical signals are widespread in insects, but those resulting in interspecific communication (i.e., synomones) remain understudied. Here, we analysed chemicals left on substrates by two species of blow fly larvae, Lucilia sericata (Meigen) and Calliphora vomitoria (Linneaus) (Diptera: Calliphoridae), which can aggregate together on carrion. Using solid-phase microextraction and dynamic headspace analysis, we identified six compounds common to both species: the decanoic, tetradecanoic, pentadecanoic, hexadecanoic and octadecanoic acids, and the 2-ethylhexyl salicylate. We then tested the behavioural effects of the decanoic and pentadecanoic acids using binary-choice experiments, along with the (Z)-9-tricosene, a pheromone found in many arthropods. The time spent by a larva and its average crawling speed were measured in two sides of an arena, where only one contained a compound at 0.25 or 25 μg/μl. No effect was observed when testing the decanoic acid. The pentadecanoic acid only reduced the speed of C. vomitoria larvae at 25 μg/μl. Finally, L. sericata larvae spent less time in the side containing the (Z)-9-tricosene at 0.25 μg/μl, whereas C. vomitoria spent more time and crawled faster in this side at 25 μg/μl. Although these results did not directly evidence synomones, they suggest that the (Z)-9-tricosene could regulate larval aggregations on carrion.     

The relationship between plasma membrane lipid composition and physical-chemical properties. I. Fluorescence polarization studies of fatty acid-altered EL4 tumor cell membranes

EL4 cells were cultured with exogenous fatty acids under conditions that resulted in their incorporation into membrane phospholipids. The behavior of the fluorescent lipid probes diphenylhexatriene and perylene was monitored in intact EL4 cells and in isolated EL4 plasma membranes. In whole cells substituted with unsaturated fatty acids, there was always a marked decrease in the $\text{P}$ value of both probes compared to the $\text{P}$ value of the probes in unsubstituted cells. In whole cells substituted with saturated fatty acids, on the other hand, $\text{P}$ values for both probes were unchanged compared to unsubstituted cells. In plasma membrane isolated from EL4 cells, no difference in $\text{P}$ values for either probe was observed among membranes from unsubstituted, saturated fatty acid substituted or unsaturated fatty acid substituted cells, even when the degree of fatty acid substitution was quite substantial. Most of the fluorescent signal for both probes in whole cells appeared to come from cytoplasmic lipid droplets. The value of techniques such as fluorescent polarization for monitoring physical properties of membranes (such as ‘fluidity’) is discussed.     

Anti-cyanobacterial fatty acids released from <Emphasis Type="Italic">Myriophyllum spicatum</Emphasis>

This study was carried out to identify unknown allelochemicals released from Myriophyllum spicatum and to investigate their anti-cyanobacterial effects. A series of analyses of culture solutions and methanol extracts of M. spicatum using gas chromatograph equipped with a mass selective detector revealed that M. spicatum released fatty acids, specifically, nonanoic, tetradecanoic, hexadecanoic, octadecanoic, and octadecenoic acids. Nonanoic, cis-6-octadecenoic, and cis-9-octadecenoic acids significantly inhibited growth of Microcystis aeruginosa, whereas tetradecanoic, hexadecanoic, and octadecanoic acids did not show any effect. When the inhibitory effect of nonanoic acid was compared with those of 4 polyphenols and eugeniin, which are anti-cyanobacterial compounds previously reported to be released by M. spicatum, nonanoic acid was found to be the most inhibitory to M. aeruginosa. These results indicate that not only polyphenols and eugeniin but also fatty acids such as nonanoic acid must be studied to reveal how M. spicatum exerts its allelopathic effect on M. aeruginosa.     

宽叶独行菜中脂肪酸的GC-MS分析

采用气质联用技术对宽叶独行菜中脂肪酸成分进行了分析,从其乙醇提取物的石油醚萃取部分共分离得到20个组分,采用面积归一化法测定了各组分的含量,其中棕榈酸(hexadecanoic acid)53.980%,硬脂酸(oc-tadecanoic acid)17.063%,二十二烷酸(docosanoic acid)4.769%,二十四烷酸(tetracosanoic acid)3.363%,二十八烷酸(octacosanoic acid)2.773%,花生酸(eicosanoic acid)2.719%,十五烷酸(pentadecanoic acid)2.476%,十七烷酸(heptadecanoic acid)2.291%。此外,三十烷酸(triacontanoic acid,十四烷酸(tetradecanoic acid),二十三烷酸(tricosanoic acid)和二十六烷酸(hexacosanoic acid)的含量均已超过了1%。     

A differential scanning calorimetry study of the interaction of free fatty acids with phospholipid membranes

Mixtures of stearic, arachic, oleic and linoleic acids with dimyristoylphosphatidylcholine (DMPC) and distearylphosphatidylcholine (DSPC) have been studied by means of differential scanning calorimetry (DSC). The mixtures of stearic (SA) and arachic acids (AA) with DMPC and DSPC show phase diagrams of the peritectic type, with a region of solid phase immiscibility from 0 to 28.5 mol% of fatty acid. A pure component, with a stoichiometry fatty acid/phospholipid (2:1) seems to be formed except for the system AA/DSPC. The mixtures of oleic (OA) and linoleic acids (LA) show complex phase diagrams. In the case of OA, different regions where a phase separation exists can be observed and for the mixture of OA with DMPC, a pure component seems to be formed with a stoichiometry OA/DMPC (1:2). LA shows different behaviour in the mixtures with DMPC and with DSPC. For the mixture, LA/DMPC, a fluid phase immiscibility region is observed over the same range of concentration as for the mixture with OA, however, the mixture with DSPC shows a solid phase immiscibility for the samples containing 45 mol% or more of LA. The interaction of the different free fatty acids with equimolar mixtures of DMPC and DSPC, showing monotectic behaviour, has also been analyzed. From our results it can be clearly concluded that saturated fatty acids partition preferentially into solid-like domains, while cis-unsaturated fatty acids partition preferentially into fluid-like domains.     

Specificity in the interaction of phospholipids and fatty acids with vesicle reconstituted cytochrome P-450. A spin label study

The association of fatty acids, androstane, phosphatidylcholine, phosphatidylethanolamine, and phosphatidic acid with purified and phospholipid-vesicle reconstituted cytochrome $\text{P-450}$ was studied by spin labeling. Spin-labeled fatty acids were found to be motionally restricted by cytochrome $\text{P-450}$ in both phospholipid vesicles and in microsomes to a much greater extent than spin-labeled phospholipids. The equilibrium of spin-labeled fatty acid between the bulk membrane lipid and the protein interface could be shifted towards an increased amount in the bulk phospholipid phase by the addition of oleic acid or lysophosphatidylcholine, but not by sodium cholate. Microsomes from different animals showed a variable extent of motional restriction of fatty acids, independent of pretreatment of the animals with phenobarbital or β-naphthoflavone, of cytochrome $\text{P-450}$ content, of the presence of type I and type II substrates for cytochrome $\text{P-450}$. These differences are attributed to the presence of varying amounts of lipid breakdown products in the microsomal membrane such as lysolipids or fatty acids which compete with the externally added spin-labeled fatty acids, or with spin-labeled androstane for the binding to cytochrome $\text{P-450}$. The negative charge of the fatty acid was found to be involved in its association with the protein. Cytochrome $\text{P-450}$ was shown to interact only with a few spin-labeled phospholipid molecules in such a way that the motional restriction of the spin acyl chains can be detected by electron paramagnetic resonance ($\text{τ}{}_{\mathrm{<mtext>R</mtext>}}\text{> 10}{}^{\mathrm{?8}}\text{s}$). The number of associated lipid molecules per protein probably is too small to form a complete shell around the protein. This lipid-protein interaction could be destroyed by the addition of sodium cholate, in contrast to the fatty acid-protein interaction.     

Amino acid stimulation of ATP cleavage by two Ehrlich cell membrane preparations in the presence of ouabain

Two membrane fractions prepared from the Ehrlich ascites-tumor cell show non-identical stimulatory responses to certain amino acids in their Mg²⁺-dependent activity to cleave ATP, despite the presence of ouabain and the absence of Na⁺ or K⁺. The first of these, previously described, shows little ($\text{Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}$)-ATPase activity, and is characteristically stimulated by the presence of certain diamino acids with low $\text{pK}{}_2$, and at pH values suggesting that the cationic forms of these amino acids are effective. The evidence indicates that these effects are not obtained through occupation of the kinetically discernible receptor site serving characteristically for the uphill transport of these amino acids into the Ehrlich cell. The second membrane preparation was purified with the goal of concentrating the ($\text{Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}$)-ATPase activity. It also is stimulated by the model diamino acid, 4-amino-1-methylpiperidine-4-carboxylic acid, and several ordinary amino acids. The diamino acids were most effective at pH values where the neutral zwitterionic forms might be responsible. Among the optically active amino acids tested, the effects of ornithine and leucine were substantially stronger for the l than for d isomers. The list of stimulatory amino acids again corresponds poorly to any single transport system, although the possibility was not excluded that stimulation might occur for both preparations by occupation of a membrane site which ordinarily is kinetically silent in the transport sequence. The high sensitivity to deoxycholate and to dicyclohexylcarbodiimide of the hydrolytic activity produced by the presence of l-ornithine and 4-amino-1-methyl-piperidine-4-carboxylic acid suggests that the stimulatory effect is not merely a general intensification of the background Mg⁺-dependent hydrolytic activity.     

Effects of free fatty acids as membrane components on permeability of drugs across bilayer lipid membranes. A mechanism for intestinal absorption of acidic drugs

Studies of the influence of fatty acids, which were the component of intestinal mucosal lipids, on the permeability of several drugs across bilayer lipid membranes generated from egg phosphatidylcholine and intestinal lipid have been pursued. The permeability coefficients of $\text{p-}\text{aminobenzoic}$ acid, salicylic acid and $\text{p-}\text{aminosalicylic}$ acid (anionic-charged drug) increased when fatty acids such as lauric, stearic, oleic, linoleic and linolenic acid were incorporated into the bilayer lipid membranes generated from phosphatidylcholine. In the presence of methyl linoleate and oleyl alcohol, no enhancing effect on $\text{p-}\text{aminobenzoic}$ acid transfer was obtained. The effect of fatty acids was more marked at pH 6.5 than at pH 4.5. In contrast, upon the addition of fatty acids to intestinal lipid membranes which originally contained fatty acids, the permeability coefficient of $\text{p-}\text{aminobenzoic}$ acid tended to decrease, though the permeability through intestinal lipid membranes was larger than that of phosphatidylcholine membranes. The permeability of $\text{p-}\text{aminobenzoic}$ acid across bilayer lipid membranes from intestinal phospholipids was significantly decreased to about equal that of phosphatidylcholine membranes, and reverted to the value of intestinal lipid membranes when fatty acids were added to intestinal phospholipids. It seemed reasonable to assume that free fatty acids in the intestinal neutral lipid fraction could contribute to the increase in the permeability of $\text{p-}\text{aminobenzoic}$ acid. On the basis of above results, possible mechanisms for good absorbability of weakly acidic drugs from the intestine are discussed.     

Utilization of C20-polyunsaturated fatty acids by a yeast fatty acid desaturase mutant

A study was made of the utilization of C₂₀-polyunsaturated fatty acids by the $\text{S. cerevisiae}$ fatty acid desaturase mutant $\text{olel-1}$, Arachidonic acid, 8,11,14-eicosatrienoic acid, and 5,8,11,14,17-eicosapentaenoic acid were about equally effective in supporting growth with lactate as the carbon source. The relative proportion of these fatty acids in total cell fatty acids was $\text{ca}$. 50%. 5,8,11-eicosatrienoic acid synthesized from oleate was less effective. Very little growth occurred with 11,14,17-eicosatrienoic acid or with 11,14-eicosadienoic acid. These results indicate the usefulness of the yeast mutant as a eucaryotic model for study of membrane systems enriched in specific C₂₀-polyunsaturated fatty acids.     

Effect of organic acid on gastrointertinal motility of rat invitro

The quantity of organic acids ( lactic acid, acetic acid, propionic acid and butyric acid ) in the content of the gastrointestinal tract of germ-free and conventional rats and the $\text{in}$$\text{vitro}$ effects of the organic acid on the motility of the gastrointestinal tract of rats were investigated.Organic acids were detected only in the gastrointestinal contents of conventional rats but not in those of germ-free rats.Lactic acid detected in the stomach of rats stimulated the motility of both small and large bowel while acetic acid, propionic acid and butyric acid found in the cecum stimulated the motility of the large bowel but not of small bowel.     

Phospholipid phase transitions. Effects of n-alcohols, n-monocarboxylic acids, phenylalkyl alcohols and quatenary ammonium compounds

The interactions of a series of alcohols, acids and quaternary ammonium salts with a phosphatidylcholine-water model biomembrane (dipalmitoyl phosphatidylcholine) system have been studied using differential scanning calorimetry. In particular the effects of these molecules upon the lipid endothermic phase transitions were investigated over a range of concentrations. A variety of effects was observed. (a) Those molecules which shift or broaden the main lipid transition can also remove the pretransition endotherm. (b) $\text{n-}\text{Alcohols}$ and $\text{n-}\text{monocarboxylic}$ acids containing the same number of carbon atoms have very similar effects at molar concentrations up to 40%. Those molecules containing 12 or more carbon atoms raise the main lipid phase transition whilst those molecules containing 10 or less carbon atoms lower this transition temperature. (c) The phase diagram of stearoyl alcohol in the phosphatidylcholine-water system shows the formation of lipid-alcohol complexes. (d) Alkyl trimethyl ammonium bromides showed behaviour which differs considerably from $\text{n-}\text{alcohols}$ and $\text{n-}\text{carboxylic}$ acids of the same chain length. (e) Other alkyltrialkyl and tetraalkylammonium bromides show that a variety of effects on the lipid phase transition can be obtained. (f) With the homologous series of phenylalkyl alcohols from benzyl alcohol to 4-phenyl butanol increasing the number of methylenes between the terminal OH and the benzene ring leads to greater interaction between solute and bilayer.The range of different effects obtained with the compounds studied offers a means for introducing various degrees and types of perturbation into membrane systems.     

Phospholipid interactions with cytochrome P-450 in reconstituted vesicles Preference for negatively-charged phosphatidic acid

Cytochrome $\text{P-450}$ LM2 was reconstituted by the cholate-dialysis method into vesicles containing a mixture of either phosphatidylcholine or phosphatidylethanolamine with up to 50 mol% of phosphatidic acid. Phase transition curves in the presence or absence of cytochrome $\text{P-450}$ were obtained from electron paramagnetic resonance experiments by measuring the partitioning of 2,2,6,6-tetramethylpiperidine-1-oxyl. Protein-free phospholipid vesicles exhibit a phase separation into domains of gel phase enriched in phosphatidic acid in a surrounding fluid matrix containing mainly phosphatidylcholine. The phase transition of the phosphatidic acid domains disappeared following incorporation of cytochrome $\text{P-450}$ into the bilayers. In contrast, in vesicles containing mixtures of egg-phosphatidic acid and dimyristoyl phosphatidylcholine, the phase transition of the domains enriched in dimyristoyl phosphatidylcholine was less sharp than in the corresponding vesicles containing cytochrome $\text{P-450}$. The results of both of these experiments could be explained by a redistribution of the mol fraction of the two phospholipids in the gel phase due to preferential binding of the egg-phosphatidic acid to the cytochrome $\text{P-450}$. For comparison, incorporation of cytochrome $\text{P-450}$ into uncharged vesicles of dimyristoyl phosphatidylcholine and egg-phosphatidylethanolamine did not alter the     

The effect of alterations in the physical state of the membrane lipids on the ability of Acholeplasma laidlawii B to grow at various temperatures

The physical state of the membrane lipids, as determined by fatty acid composition and environmental temperature, has a marked effect on both the temperature range within which Acholeplasma laidlawii B cells can grow and on growth rates within the permissible temperature ranges. The minimum growth temperature of 8 °C is not defined by the fatty acid composition of the membrane lipids when cells are enriched in fatty acids giving rise to gel to liquid-crystalline membrane lipid phase transitions occurring below this temperature. The elevated minimum growth temperatures of cells enriched in fatty acids giving rise to lipid phase transitions occurring at higher temperatures, however, are clearly defined by the fatty acid composition of the membrane lipids. The optimum and maximum growth temperatures are also influenced indirectly by the physical state of the membrane lipids, being significantly reduced for cells supplemented with lower melting, unsaturated fatty acids. The temperature coefficient of growth at temperatures near or above the midpoint of the lipid phase transition is 16 to 18 $\text{kcal}\text{mol}$, but this value increases abruptly to 40 to 45 $\text{kcal}\text{mol}$ at temperatures below the phase transition midpoint. Both the absolute rates and temperature coefficients of cell growth are similar for cells whose membrane lipids exist entirely or predominantly in the liquid-crystalline state, but absolute growth rates decline rapidly and temperature coefficients increase at temperatures where more than half of the membrane lipids become solidified. Cell growth ceases when the conversion of the membrane lipid to the gel state approaches completion, but growth and replication can continue at temperatures where less than one tenth of the total lipid remains in the fluid state. An appreciable heterogeneity in the physical state of the membrane lipids can apparently be tolerated by this organism without a detectable loss of membrane function.     

Identification and characterization of a new methylated amino acid in ribosomal protein L33 of Escherichiacoli

Methylated amino acids from ribosomal protein L33 of various $\text{Escherichia}\text{coli}$ strains (Q13, B and MRE600) were analyzed. It was found that while protein L33 from $\text{E.}\text{coli}$ Q13 contains two methylated neutral amino acids (peaks I and II), only one methylated neutral amino acid (peak I) was found in protein L33 derived from both $\text{E.}\text{coli}$ strains B and MRE600. The methylated amino acid present in peak I was identified as N-monomethylalanine by ion-exchange column chromatography, high-voltage paper electrophoresis and descending paper chromatography using different solvent systems. This marks the first time that N-monomethylalanine was found in any ribosomal protein.     

Methionine transport in S37 cells. Substrate-dependent function of amino acid transport system A in exchange processes

Methionine had been observed to interact with two principal transport systems for amino acids in mammalian cells, the A and L systems. The present study of methionine transport and of exchange processes through system A arose in the course of a study to define the specificity of a transinhibition effect caused by cysteine.Methionine uptake through two transport systems in the S37 cell was confirmed by the occurrence of a biphasic double-reciprocal plot for labeled methionine uptake. Preloading cells with methionine stimulated labeled histidine uptake through both systems A and L. Efflux of labeled methionine from cells was stimulated by histidine in a biphasic manner, so that both systems A and L can be used for exchange when methionine is the intracellular amino acid. Aminocycloheptanecarboxylic acid elicited exchange efflux of labeled methionine only through system L. α-Aminoisobutyric acid and $\text{N-}\text{methyl}\text{-α-}\text{aminoisobutyric acid}$ both stimulated efflux of labeled $\text{N-}\text{methyl}\text{-α-}\text{aminoisobutyric acid}$ from S37 cells. These findings are interpreted a showing that transport system A is capable of functioning as an exchange system depending upon the identity of intracellular and extracellular substrates available.     

Growth inhibition of Halobacterium cutirubrum by cerulenin,a potent inhibitor of fatty acid synthesis

The polar lipids of $\text{Halobacterium cutirubrum}$ are known to consist exclusively of diether derivatives of glycerol, and do not contain fatty acids. However, cerulenin, a specific and potent inhibitor of fatty acid synthesis, was shown to inhibit the growth of this organism. Protection from growth inhibition was demonstrated when fatty acids of 18 carbons were added to the growth medium, but not when palmitic or palmitoleic acids were used. Cerulenin appears to affect synthesis of all polar lipids in this organism while relative levels of protein and nucleic acids were not significantly affected. Growth inhibition by cerulenin supports the conclusion that the fatty acid synthetase system present in $\text{H. cutirubrum}$ is necessary for lipid biosynthesis, despite the fact that fatty acids are not structural components of the lipids of this bacterium. A pathway is proposed to account for these observations.