Janette R. Kenrick

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.

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

Abstract 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.

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

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 .

Monolayer and 13C nuclear magnetic resonance studies on the interaction between melittin and chloroplast lipids

Abstract The interaction of the polypeptide melittin with chloroplast membrane lipids has been studied by monolayer and 13 C-NMR techniques. Under conditions favouring the existence of a melittin monomer, the interaction of the polypeptide with monolayers of chloroplast lipids is largely confined to negatively charged lipids. Conditions favouring the formation of the melittin tetramer result in a marked interaction of the polypeptide with monolayers of uncharged lipids. 13 C-NMR measurements of the rate of motion of fatty acyl carbon atoms in multibilayers of chloroplast membrane lipids demonstrate that melittin penetrates deeply into the bilayer irrespective of the proportion of negatively charged lipids. It is concluded that interaction of melittin which chloroplast membrane lipids is the primary factor in its capacity to inhibit membrane-associated reactions in chloroplasts.

Melittin : an inhibitor of chloroplast photochemical reactions.

Abstract Melittin, a polypeptide component of bee venom, is an inhibitor of photochemical reactions in chloroplasts isolated from higher plants. At concentrations around 5 μM, melittin acts as an uncoupler of photophosphorylation and abolishes the 518 nm light induced absorbance changes. At higher concentrations (30–50 μM), melittin abolishes both the light-induced photooxidation of cytochrome f , and partially inhibits other reactions of photosynthetic electron transfer, without causing lysis of the membrane. The observed inhibitions appear to be due to changes in the properties of the membrane lipid bilayer, caused by penetration of melittin molecules.

Preparation and comparison of model bilayer systems from chloroplasts thylakoid membrane lipids for 13C-NMR studies

Model bilayer systems from individual purified chloroplast thylakoid membrane lipids, from reconstituted mixtures of these purified lipids, and from leaf total polar lipid extracts have been prepared in water, and the longitudinal relaxation times (T1s) of the individual carbon atoms of the fatty acyl chains measured by 13C-NMR spectroscopy. The T1s increase with increasing distance of the carbon atoms from the polar headgroups in all cases, and as the results from each of the preparations are similar, all can be used as models of chloroplast membrane bilayers. Relaxation time measurements on intact chloroplast thylakoid membranes indicate the presence of chlorophyll resonances in the 13C-NMR spectrum of the membrane.