Effect of hydration on the structure, dynamics and function of photosynthetic membranes of purple bacteria

NMR spectra and relaxation times T1 and T2 for 31P in membranes of Rhodobacter sphaeroides were investigated at different relative humidity levels. The results are compared to the hydration curves, fatty acid composition and the structure-dynamic and functional characteristics of the membranes of photosynthetic bacteria Rb. sphaeroides, Rhodospirillum rubrum and Ectothiorhodospira shaposhnikovii. The differences in the state of lipid phase of these membranes are revealed under low humidity, and this is conducive to variability of their structural dynamic and functional characteristics during the hydration process. Based on the results obtained and the data on model systems, four stages of hydration process are distinguished with different effects on the structure and dynamics of membrane components. These stages are: hydration of a portion of polar groups, involvement of water molecules in the hydrogen bonds within macromolecules and the lipid phase, hydration of all polar groups with the appearance of water with high dielectric constant thus making possible the lateral diffusion within the membrane and realization, through water participation, of conditions within organelles and cells required for the process regulation at these levels. The mechanism of water action on various membrane components and their dynamics at each stage are discussed, as well as the effect of different types of motion on the efficiency and regulation of electron transport in the photosynthetic chain of the membranes studied.