Effects of fatty acid from deep-sea microorganisms on lipid bilayer membrane fluidity under high pressure: comparison of branched-chain and polyunsaturated fatty acid

In this study, the effects of unsaturated and saturated branchedchain fatty acids in biomembranes of microorganisms living under high temperature and high pressure on the fluidity of biomembranes were investigated by time-resolved fluorescence anisotropy measurements. First, the relationship between the order parameter S and the rotational diffusion coefficient Dw, which can be calculated from the fluorescence anisotropy measurements, and the motion of lipid molecules was investigated using lipids with three different structures, and it was found that the former was related to the spacing of lipid molecules and the latter to the motion of lipid molecules. Next, we investigated the S and Dw values of lipid bilayer membrane containing the saturated branched-chain fatty acid 12-methyltridecanoic acid (12-MTA) and the polyunsaturated fatty acid (PUFA) cis-4,7,10,13,16,19-docosahexaenoic acid (DHA). The results showed that 12-MTA increased the S value and decreased the Dw value. On the other hand, DHA tended to reduce the S value and increase the Dw value, albeit slightly. These results mean that 12-MTA narrows the molecular spacing of lipids and inhibits lipid molecular movement, while DHA tends to widen the molecular spacing of lipids and promote lipid molecular movement