MECHANISMS OF HYDRATION EFFECTS ON THE STRUCTURAL DYNAMIC AND FUNCTIONAL-CHARACTERISTICS OF PHOTOSYNTHETIC MEMBRANES IN VARIOUS PURPLE BACTERIA

NMR spectra and T-1, T-2 relaxation times for H-1, C-13 and P-31 nucle i in membranes of R. rubrum and Rb. sphaeroides recorded at different relative humidity, as well as hydration curves and electron transfer e fficiency of these membranes and membranes of E. shaposhnikovii, revea l complicated relations between structural-dynamic and functional char acteristics. A number of sites of the electron transfer chain are show n to be under the control of structural-dynamic mechanisms. Different parameters characterizing these membranes at low humidity and during h ydration have been established. These findings and analysis of the dat a from model systems reveal four different stages of hydration. Each o f them is associated with specific changes in structure, dynamics, and function of photosynthetic membranes and their components. In the fir st stage the hydration of some polar groups leads to local changes in the dynamics of the protein component and this influences the recombin ation between photoactive pigment P and intermediate acceptor Q(A). Th e second stage is induced by incorporation of water molecules into the hydrogen bonds between the polar head groups of the lipids and within macromolecules. This results in changes of the dynamics of the membra nes, the efficiency of the electron transfer between the quinones and the efficiency of photooxidation of cytochrome c. In the third stage a ll polar groups are hydrated owing to the appearance of free water wit h a high dielectric constant. This makes possible lateral mobility of membrane components and changes in distances between the interacting m acromolecular components. Therefore, the regulation of photosynthetic processes can be mediated with the participation of mobile carriers. F inally, in the fourth stage, complete humidification provides conditio ns for regulation of photosynthesis at the cell level. The mechanisms influencing these processes and the efficiency and regulation of elect ron transfer in various parts of the photosynthetic chain are discusse d.