ELSEVIER Biochimica et Biophysica Acta 1187 (1994) 89-93 BB Biochi~ic~a et Biophysica A~ta Rapid Report Distance between tyrosines Z ÷ and D ÷ in plant Photosystem II as determined by pulsed EPR Andrei V. Astashkin 1, Yoshio Kodera, Asako Kawamori * Faculty of Science, Kwansei Gakuin University, Uegahara 1-1-155, Nishinomiya 662, Japan Received 1l April 1994 Abstract A '2+ 1' electron spin echo method was applied to estimate the dipole interaction between tyrosines D ÷ and Z ÷ in Mn-depleted preparations of plant Photosystem II. The value of dipole interaction obtained corresponds to the distance of approx. 30 ,~ between the two types of tyrosine radical. Key words: Photosystem II; Structural organization; Tyrosine D; Tyrosine Z; EPR, pulsed The information about the structural organization of plant Photosystem II is essential for better understand- ing of the mechanism of the light-induced chemical reactions leading to water oxidation and release of free oxygen molecules. With the lack of X-ray data for PS II, the structural information can be obtained by alter- native methods, including IR, EXAFS and EPR spec- troscopies. In recent years EPR has been extensively applied to clarify the nature and function of various components of the charge transfer chain in PS II (for review see Ref. [1]) and to estimate the distances between them [2-8]. Two types of tyrosine radical in PS II, Y~ and Y~, are known to give almost identical EPR spectra with a g-factor close to 2.0046, width of about 2 mT and partially resolved hyperfine structure of four lines [9- 11]. These tyrosines belong to D 1 (Yz) and D 2 (YD) * Corresponding author. Fax: + 81 798 510914. 1 On leave from Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, 630090 Novosibirsk, Russia. Abbreviations: PS I1, Photosystem II; Chl, chlorophyll; P680, primary electron donor in Photosystem II; Yz, tyrosine Z electron donor in Photosystem II; Yo, tyrosine D electron donor in Photosys- tern II; OEC, oxygen-evolving complex; Mops, morpholinopropane- sulfonic acid; m.w., microwave; hfi, hyperfine interaction; EPR, electron paramagnetic resonance; ESE, electron spin echo; ENDOR, electron-nuclear double resonance; EXAFS, extended X-ray absorp- tion fine structure; IR, infrared. 0005-2728/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0005-2728(94)001 12-1 proteins and are thought to be located symmetrically with respect to the primary electron donor P680 [12- 15]. Even with this symmetric arrangement, Yo and Yz have different functions in PS II. Yz acts as an inter- mediate redox-active species in the electron transfer from the manganese cluster in OEC to the photo- oxidized P680. The other tyrosine, YD, does not di- rectly participate in the reactions related to the oxygen evolution and its role in PS II is rather unclear. At room temperature, YD is oxidized with a characteristic time of one second and rereduced within tens of min- utes [16,17], giving rise to easily observable EPR signal (Signal IIslow). The corresponding values for Yz in intact PS II are nanoseconds and hundreds of mi- croseconds [10,18,19], and its EPR signal (Signal live ~ fast) can be observed only with difficulty. The difference in the properties of YD and Yz could probably be understood if more information about the structure of their local surroundings and about their spatial positions with respect to other electron carriers in PS II were available. The studies of Y~ and Y~ by EPR, ENDOR and IR spectroscopies [11,20,21] have shown some differences in their local structures. How- ever, these data are too scarce to explain the functional difference between the tyrosines. The measurement of relative positions of the tyrosines with respect to other electron carriers is a part of the problem of the global mapping of PS II. Some steps in this direction have already been taken and the distances between Y~ and