Lipid composition and physico-chemical properties of gill mitochondrial membranes from Ruditapes philippinarum

In this study we compared the mitochondrial membranes from gills of Philippine clam Ruditapes philippinarum and of the Mediterranean mussel Mytilus galloprovincialis analyzing the lipid composition and the physico-chemical state of both membranes and liposomes prepared from the total lipids extracted from mitochondria. Fatty acid and sterol analyses were carried out as in a previous work. Physico-chemical studies of isolated membranes and liposomes were performed at three temperatures (10,20,30 °C) by using 2-dimethylamino-(lauroyl)-naphtalene (Laurdan) as fluorescent probe which is located at the polar headgroups level. Although both species exhibit the typical fatty acid pattern of marine invertebrates with high levels of n-3 PUFA, the fatty acid composition resulted deeply “species-oriented”. The different fatty acid profile could mirror, other than the different habitats and feeding habits, also a species-specific biosynthetic pattern. Sterol composition was more diversified in R. philippinarum than in M. galloprovincialis and in both species more than 50% sterols were different from cholesterol (57,9 and 55% respectively). Although mitochondrial membranes of both species were in a liquid-crystalline phase, in Ruditapes philippinarum the physical state was much more sensitive to temperature and less rigid than that in Mytilus galloprovincialis. Moreover liposomes prepared from mitochondrial total lipids of both species showed peculiar differences of the physical phase.