Heterogeneity of Thylakoid Membranes Studied by EPR Spin Probe

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S. M. Kochubey^1*, A. I. Vovk², O. Yu. Bondarenko¹, V. V. Shevchenko¹, R. V. Bugas², A. K. Melnyk², and V. Yu. Tanchuk²

¹Institute of Plant Physiology and Genetics, National Academy of Sciences of Ukraine, Vasilkovskaya str. 31/17, 03022 Kiev, Ukraine; fax: 380 (44) 258-8146; E-mail: skbiofis@naverex.kiev.ua

²Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, Murmanska str. 1, 02660 Kiev, Ukraine; fax: 380 (44) 573-2552; E-mail: vovk@bpci.kiev.ua

^* To whom correspondence should be addressed.

Received November 14, 2006; Revision received January 23, 2007

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A lipophilic nitroxyl radical, 1-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 originate from grana and the grana core regions. The binding of the spin probe to the membranes was revealed by specific changes in a shape of the EPR spectra. A share of membrane-bound spin probe was different for chloroplasts and subchloroplast fragments, as well as its rotational correlation time and apparent enthalpy and entropy activation of nitroxide rotational motion. The binding of the spin probe induced a significant decrease in the amount of the oxidized P700 and changes in the kinetics of its light oxidation and dark recovery. This suggests that one of the sites of nitroxyl radical binding is the nearest surrounding of the pigment-protein complexes of Photosystem I (PSI). Distinctions in mobility of spin probe immobilized by chloroplasts and their fragments can be caused by the different environment of the PSI complexes located in various regions of thylakoid membranes.

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KEY WORDS: chloroplasts, EPR, Photosystem I, spin probe, thylakoids

DOI: 10.1134/S0006297907050136

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