HETEROGENEITY OF THYLAKOID MEMBRANES STUDIED BY EPR SPIN PROBE
Lipophilic nitroxyl radical, l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 1-adamantylacetate has been applied to EPR spin probe study of chloroplasts and subchloroplast fragments of different types. The latter were represented by grana and grana core particles. The binding of the spin probe to membranes in the investigated objects was revealed by spe-cific changes in a shape of EPR spectra. The share of membrane bound spin probe was different for chloroplasts and subchloroplast fragments as well as values of its rotational correlation time and values of apparent enthalpy and entropy activation of nitroxide rotational motion. The binding of the spin probe induced a significant decrease in the amount of oxidized P700 and changes in shape of the kinetics of its light oxidation and dark recovery. This suggests that one of the possible sites of the nitroxyl radical binding is the nearest surrounding of the pigment-protein com-plexes of Photosystem 1. The nature of the binding sites are assumed to be different for Photosystem 1 complexes located in various regions of thylakoid membranes.