David G. Bishop

Fatty acid composition of symbiotic zooxanthellae in relation to their hosts.

Gymnodinoid dinoflagellate symbionts, commonly referred to as zooxanthellae, are widely distributed among marine invertebrates. It has been assumed that they represent only one species,Gymnodinium microadriaticum. The fatty acid composition of total lipids and galactolipids of zooxanthellae isolated from 8 species of corals, 3 species of clams and a foraminiferan have been analyzed and found to vary according to the host. For example, the content of eicosapentaenoic acid in clam zooxanthellae monogalactosyldiacylglycerol was less than 2%, whereas in the same lipid from coral zooxanthellae, the content ranged from 9 to 22%. Corresponding values for the acid in digalactosyl-diacylglycerol were 1–8% from clam zooxanthellae and 23–40% from coral zooxanthellae. Coral zooxanthellae monogalactosyldiacylglycerol contain higher levels of octadecatetraenoic acid than are found in digalactosyldiacylglycerol, whereas the reverse is true in clam zooxanthellae. The fatty acid composition of the lipids of an axenic culture of zooxanthellae isolated from the clamTridacna maxima are similar to those of cells freshly isolated from the host. The results suggest either that the host is capable of affecting the fatty acid metabolism of the symbiont or that different strains of zooxanthellae occur in corals and clams.

Monolayer properties of chloroplast lipids

The properties of seven monogalactosyldiacylglycerols and six digalactosyldiacylglycerols, isolated from photosynthetic membranes and possessing different levels of fatty acid unsaturation, have been studied by the monolayer technique and compared with those of the fully saturated compounds. In addition, the monolayer properties of sulphoquinovosyldiacylglycerols and phosphatidylglycerols from higher plant chloroplasts, and several hexadecenoic acids have been measured. Monogalactosyldiacylglycerols containing saturated fatty acids form a condensed monolayer similar to that of saturated phosphatidylcholines. The naturally occurring monogalactosyldiacylglycerols, of which the double bond index ranged from 0.6 to 3.9, possessed comparable force-area curves suggesting that headgroup interactions play a more important role in packing behaviour than in phosphatidylcholines. Although digalactosyldiacylglycerols containing fully saturated fatty acids form a more expanded monolayer than the corresponding monogalactosyldiacylglycerols, the degree of expansion of the monolayer due to the presence of unsaturated fatty acids in the naturally occurring digalactosyldiacylglycerols is much less than in monogalactosyldiacylglycerols. Monogalactosyldiacylglycerols and digalactosyldiacylglycerols from a single species have very similar monolayer properties, and the presence of sulphoquinovosyldiacylglycerols and phosphatidylglycerols in the proportions in which they occur in higher plant chloroplasts does not have any condensing effect on a monolayer of galactolipids.

The distribution of galactolipids in mesophyll and bundle sheath chloroplasts of maize and sorghum

Abstract The galactolipid content of bundle sheath chloroplasts is significantly higher, on a chlorophyll basis, than that of mesophyll chloroplasts in both maize and sorghum. It is suggested that the molar ratio of galactolipid to chlorophyll reflects the degree of grana formation in a chloroplast.

Changes in the lipid composition of ripening banana fruits and evidence for an associated increase in cell membrane permeability

The content of total lipid in banana fruit pulp tissue remained constant during the climacteric rise induced by applied ethylene. The relative proportions of neutral lipid, glycolipid and phospholipid did not change. However, the fatty acid composition of the lipid did change during ripening. This change was confined largely to the phospholipid fraction, in which there was an increase in the proportion of linolenic acid and a decrease in the proportion of linoleic acid. The net result was an increase in total unsaturation of the fatty acids in the phospholipid fraction. Measurements of spin label motion in liposomes prepared from banana phospholipids showed that the motion and fluidity of bilayer lipids increased during ripening of the fruit from which the liposomes were prepared, probably as a result of increased lipid unsaturation during ripening. Since increases in membrane fluidity are accompanied by increases in the passive permeability to small molecules in a number of membrane systems, it is suggested that the increased leakage which has been previously demonstrated in ripening banana fruit tissue is due to increases in the permeability of at least some cell membranes.

Thermal properties of 1-hexadecanoyl-2-trans-3-hexadecenoyl phosphatidylglycerol

Abstract Techniques are described for the isolation of 1-hexadecanoyl-2- trans -3-hexadecenoyl phosphatidylglycerol and trans -3-hexadecenoic acid, using r

The role of lysophosphatidylcholine in lipid synthesis by developing sunflower (Helianthus annuus L.) seed microsomes

The incorporation of oleate from oleoyl-CoA into lipids by microsomes from developing sunflower (Helianthus annuus L.) seeds has been investigated. Oleate was incorporated mainly into position 2 of phosphatidylcholine or released as free fatty acid. The addition of exogenous 1-acyl-lysophosphatidylcholine increased the incorporation of oleate into position 2 of phosphatidylcholine and decreased the release of free oleate. In the absence of exogenous lysophosphatidylcholine, the incorporation of oleate into phosphatidylcholine was limited by the amount of endogenous acceptor present. DH-990, an inhibitor of acyl-CoA:lysophosphatidylcholine acyltransferase, almost completely inhibited the incorporation of oleate from oleoyl-CoA into phosphatidylcholine at a concentration of 2.5 mM. These results indicate that the incorporation of oleate from oleoyl-CoA into microsomal phosphatidylcholine occurs mainly by the acylation of a 1-acyl-lysophosphatidylcholine acceptor rather than by acyl exchange between oleoyl-CoA and phosphatidylcholine. While the incorporation of oleoyl-CoA was completed within 2 to 5 min, exogenous 1-acyl-lysophosphatidylcholine was incorporated into phosphatidylcholine for up to 30 min. Addition of oleoyl-CoA resulted in an increase in both the rate and magnitude of lysophosphatidylcholine incorporation, which could not be accounted for by a stoichiometric reaction between the two substrates. Evidence is provided that free CoA had an independent stimulatory effect on the incorporation of lysophosphatidylcholine. The implications of this finding are discussed.

Fatty acid composition of the lipids of Puffinus tenuirostris (Temminck) in relation to its diet

Abstract The fatty acid composition of lipids isolated from the depot fat, stomach contents, and proventricular oil of adult and chick Puffinus tenuirostris (Temminck) has been analysed. The diet of both adults and chicks is almost exclusively derived from the euphausiid Nyctiphanes australis Sars, and an attempt was made to determine whether dietary lipid affects the composition of depot fat, and whether individual fatty acids in the stomachs and proventricular oil can be used as markers for the origin of the diet. An apparent selectivity in the deposition of fatty acids in the fat depots can be explained by the conversion of fatty alcohols, derived from the euphausiid wax ester, into fatty acids of equivalent chain length and unsaturation. Hexadecadienoic acid appeared to be the only possible marker fatty acid from the euphausiid, but wide variations in its level limits its usefulness as a reliable index of the diet of Puffinus tenuirostris .

Interaction of the polypeptide cardiac stimulant anthopleurin-A with H+, Ca2+, and membrane lipids.

Abstract Natural-abundance 13 C NMR spectroscopy at 15.04 MHz has been used to examine the effects of pH, calcium, and lanthanide ions on the polypeptide cardiac stimulant Anthopleurin-A in aqueous solution. The carboxyl resonance from the aspartic acid residue not observed in a previous study ( R. S. Norton and T. R. Norton, 1979, J. Biol. Chem. 254 , 10220–10226 ) has been identified and an apparent p K a of 3.4 obtained. More accurate estimates have been derived for the apparent p K a values of the two histidine residues. Binding of Ca 2+ ions has been found by equilibrium dialysis and 13 C NMR to be weak ( K d > 0.1 M). The interaction with lanthanide ions is slightly stronger, but binding occurs at the C terminus as well as at a site involving one or both of the aspartate carboxylate groups. These results suggest that possible Anthopleurin-A-induced calcium translocation in the myocardial cell is a secondary effect. The interaction of Anthopleurin-A with lipid monolayers has also been examined. Binding occurs to neutral and zwitterionic lipids, but is stronger with negatively charged lipids, particularly cardiolipin. This interaction is also influenced by the presence of Ca 2+ ions. The implications of these results for the mechanism of action of this polypeptide are discussed.

Effect of amphotericin B on membrane-associated photosynthetic reactions in maize chloroplasts

Abstract The effect of the polyene antibiotic amphotericin B on membrane-associated photosynthetic reactions in maize mesophyll chloroplasts has been investigated. Both the rate and extent of cytochrome f oxidation are diminished by treatment with the antibiotic, but can be restored to that of control chloroplasts by addition of exogenous plastocyanin. The assay of C550 at liquid nitrogen temperatures showed that the primary photochemistry of photosystem 2 is not damaged by the antibiotic treatment. Both the fast and slow components of the light-induced absorbance change at 515 nm are decreased by treatment of the chloroplasts with the antibiotic, as is the ability to establish a proton gradient. Measurement of the motion of lipid spin labels in chloroplasts and in liposomes prepared from chloroplast lipids has demonstrated that amphotericin B causes a decrease in the fluidity of the lipid bilayer. It is concluded that the effect of amphotericin B on chloroplast localized reactions is due to an intercalation of the antibiotic into the lipid phase of the membrane. The resulting change in membrane fluidity renders the membrane unable to maintain a charge differential or a proton gradient, and leads to the inhibition of photosynthetic electron transfer as a result of the release of plastocyanin from its site in the membrane. The results support the concept that plastocyanin is located close to the surface of the chloroplast membrane.

The site of inhibition of photosynthetic electron transfer by amphotericin B.

Abstract The inhibitory effect of the polyene antibiotic, amphotericin B, on photosynthetic electron transfer has been investigated. Treatment of chloroplasts with the inhibitor results in the release of plastocyanin from its site in the chloroplast membrane. This release is accompanied by a shift in the pH curve for ferricyanide photoreduction from water, which is similar to that observed when chloroplasts are treated by sonication or passage through a French press. Delayed light emission from photosystem 2 is not destroyed by amphotericin B treatment, indicating that photosystem 2 is not damaged. Amphotericin B does not inhibit photoreduction of ferricyanide from water by chloroplast preparations which are deficient in plastocyanin, such as maize bundle-sheath chloroplast fragments, Euglena chloroplasts, or maize mesophyll chloroplasts passed through a French press. Chloroplasts treated with amphotericin B are not able to photooxidize plastocyanin. This result demonstrates that little structural damage occurs to the membrane during treatment with the antibiotic as a capacity to photooxidize plastocyanin is observed only in damaged chloroplast membranes.