Studies on Acholeplasma laidlawii grown on branched-chain fatty acids

The hydrocarbon chain orientational order parameters of membranes of Acholeplasma laidlawii B enriched with large quantities of a linear saturated, a methyl iso-branched, or a methyl anteiso-branched fatty acid plus small quantities of various isomeric monofluoropalmitic acid probes were determined via fluorine-19 nuclear magnetic resonance spectroscopy (19F NMR) over a range of temperatures spanning the gel to liquid-crystalline phase transitions (determined by differential scanning calorimetry). Membrane orientational order profiles in the liquid-crystalline state were generally similar regardless of the particular fatty acyl structure, showing a region of relatively constant order preceding a region of progressive decline in order toward the methyl terminus of the acyl chain. In the gel state, the order profile of the linear saturated fatty acid enriched membranes was characteristically flat, with little head to tail gradation of order. In contrast, the methyl iso-branched and the methyl anteiso-branched enriched membranes exhibited a local disordering in the gel phase reflected in a very pronounced head to tail gradient of order, which remained at temperatures below the lipid phase transition. In addition, the methyl iso- and anteiso-branched fatty acid enriched membranes were overall more disordered than the membrane containing only linear saturated fatty acyl groups. Thus, at a constant value of reduced temperature below the lipid phase transition, overall order decreased in the progression 15:0 greater than 16:0i greater than 16:0ai, suggesting that these methyl-branched substituents lower the lipid phase transition by disrupting the gel phase lipid chain packing.(ABSTRACT TRUNCATED AT 250 WORDS)

Section: Resultsmentioning

confidence: 99%

Fluorine-19 nuclear magnetic resonance studies of lipid fatty acyl chain order and dynamics in Acholeplasma laidlawii B membranes. Gel-state disorder in the presence of methyl iso- and anteiso-branched-chain substituents

Macdonald¹,

Sykes²,

McElhaney³

1985

“…Several lines of evidence indicate that branched-chain fatty acids, in the gel state, occupy a larger area in the bilayer than do linear saturated fatty acids. Wide-angle X-ray diffraction experiments indicate that the sharp 4.2-Á reflection associated with reflections from closely packed hydrocarbon chains in gel-state lipids is replaced by a broader reflection with a spacing of 4.3-4.4 Á in biological membranes naturally or artificially enriched with branched-chain fatty acids (Haest et al, 1974;Bouvier et al, 1981). Pig pancreatic phospholipase A2, which cannot hydrolyze gel-state phosphatidylglycerol in A. laidlawii membranes enriched with linear, saturated, or unsaturated fatty acids, can attack this phospholipid in membranes enriched with branched-chain fatty acids, even at temperatures below the phase transition lower boundary temperature (Bouvier et al, 1981).…”

Section: Discussionmentioning

confidence: 99%

Fluorine-19 nuclear magnetic resonance studies of lipid fatty acyl chain order and dynamics in Acholeplasma laidlawii B membranes. Effects of methyl-branch substitution and of trans unsaturation upon membrane acyl-chain orientational order

Macdonald¹,

McDonough²,

Sykes³

et al. 1983

The hydrocarbon-chain orientational order parameters of membranes of Acholeplasma laidlawii B enriched with straight-chain saturated, methyl iso-branched, methyl anteiso-branched, or trans-unsaturated fatty acids have been determined via fluorine-19 nuclear magnetic resonance spectroscopy (19F NMR). A theoretical description of the 19F NMR spectral line shape is presented that permits the determination of the orientational order parameters associated with specifically monofluorinated palmitic acid probes biosynthetically incorporated into membrane glycerolipids. Membrane orientational order profiles determined by 19F NMR in the case of straight-chain saturated fatty acid enrichment were qualitatively similar to profiles obtained by 2H NMR. The methyl iso-branch and methyl anteiso-branch structural substituents induced a local ordering while the trans double bond substituent induced a local disordering evident from alterations to the character of the orientational order profile. These various effects could be understood in terms of an altered probability of the occurrence of rotational isomerization in the presence of particular substituents. At 37 degrees C the overall orientational order decreased in the progression eta-acyl greater than iso branched greater than anteiso branched greater than or equal to trans double bonded. The relative overall order was then a direct function of the relative proximity of the membrane lipids to their respective gel to liquid-crystalline phase transitions. When observed at Tm + 15 degrees C, where the different species of fatty acids could be considered to be in a comparable thermodynamic state, the overall order decreased in the progression anteiso branch greater than trans double bond greater than iso branch greater than eta-acyl.(ABSTRACT TRUNCATED AT 250 WORDS)

“…In addition, these studies indicated that branched-chain lipids adopt a loosely packed gel-state conformation prior to the melting of the acyl chains. The latter was also inferred from studies on monolayer films composed of branched-chain phosphatidylcholines (Kannenberg et al, 1983;Suzuki & Cadenhead, 1985) and observations on biological membranes that were highly enriched in iso-and anteisobranched-chain fatty acids (Haest et al, 1974;Legendre et al, 1980;Silvius & McElhaney, 1980a;Bouvier et al, 1981;Macdonald et al, 1985). Indeed, some studies have also hinted at the possibility that, in the liquid-crystalline state, branched-chain lipids may be more ordered than straight-chain lipids at comparable reduced temperatures (Macdonald et al, 1983;Suzuki & Cadenhead, 1985).…”

mentioning

confidence: 85%

Thermotropic phase behavior of model membranes composed of phosphatidylcholines containing dl-methyl anteisobranched fatty acids. 1. Differential scanning calorimetric and phosphorus-31 NMR spectroscopic studies

Lewis¹,

Sykes²,

McElhaney³

1987

The thermotropic phase behavior of aqueous dispersions of nine dl-methyl branched anteisoacylphosphatidylcholines was studied by differential scanning calorimetry and 31P nuclear magnetic resonance spectroscopy. The calorimetric studies demonstrate that these compounds all exhibit a complex phase behavior, consisting of at least two minor, low-enthalpy, gel-state transitions which occur at temperatures just prior to the onset of the gel/liquid-crystalline phase transition. In addition, at still lower temperatures, anteisobranched phosphatidylcholines containing fatty acyl chains with an odd number of carbon atoms show a major, higher enthalpy, gel-state transition, which was assigned to a conversion from a condensed to a more loosely packed gel phase. No such transition was observed for the even-numbered compounds in aqueous dispersion, but when dispersed in aqueous ethylene glycol, a major gel-state transition is clearly discernible for two of the even-numbered phospholipids. The major gel-state transition exhibits heating and cooling hysteresis and is fairly sensitive to the composition of the bulk aqueous phase. 31P NMR spectroscopic studies indicate that the major gel-state transition is accompanied by a considerable change in the mobility of the phosphate head group and that, at temperatures just prior to the onset of the gel/liquid-crystalline phase transition, the mobility of the phosphate head group is comparable to that normally exhibited by the liquid-crystalline state of most other phospholipids. The temperatures at which the gel/liquid-crystalline phase transition occurs and the enthalpy change associated with this process are considerably lower than those of the saturated n-acyl-PC's of comparable acyl chain length.(ABSTRACT TRUNCATED AT 250 WORDS)