245 GHz High-Field EPR Study of Tyrosine-D° and Tyrosine-Z° in Mutants of Photosystem II

Publisher Website
Google Scholar
Abstract
A 245 GHz 8.7 T high-field EPR study of tyrosine-D (TyrD°) and tyrosine-Z (TyrZ°) radicals of photosystem II (PSII) from Synechocystis PCC 6803 was carried out. Identical principal g values for the wild-type Synechocystis and spinach TyrD° showed that the two radicals were in similiar electrostatic environments. By contrast, the principal g values of the TyrD° in the D2-His189Gln mutant of Synechocystis were different from those of the wild-type and spinach radicals and were similar to those of the tyrosyl radical in ribonucleotide reductase. These comparisons indicate that the D2-His189Gln mutant TyrD° is not hydrogen-bonded or is only weakly so. The HF-EPR spectrum of TyrZ° was obtained from the D2-Tyr160Phe mutant that lacks TyrD°. The principal g values were nearly identical to those of the wild-type TyrD°. The low-field edge of the TyrZ° spectrum was much broader than at the other two principal g values and was also much broader than the TyrD° spectrum. From the identical g values and previous work on tyrosyl radical g values [Un S., Atta M., Fontecave, M., & Rutherford, A. W. (1995) J. Am. Chem. Soc. 117, 10713−10719], it was concluded that TyrZ° , like TyrD°, is hydrogen-bonded. The broadness of the gx component was interpreted as a distribution in strength of the hydrogen-bonding due to disorder in the protein environment about TyrZ°.

This publication has 11 references indexed in Scilit: