Thermotropic behaviour of membrane lipids from brown marine alga Laminaria japonica

Microcalorimetry was used to show that transition-temperature ranges of phospho- and glycolipids of the brown marine alga Laminaria japonica were similar (from –62 to –47°C up to 62– 65°C), except for monogalactosyldiacylglycerol, the low-temperature limit of which was shifted to –78°C. As was shown by polarizing microscopy, the low-enthalpy peaks at temperatures of approx. 30–45°C corresponded to isotropic melting of galactolipids and coincided with the hightemperature limit for photosynthetic and mitochondrial activity of the algae. As a whole, a classical interrelation was observed between thermotropic behaviour and the fatty acid unsaturation of lipids.