Abstract:
:Photosystem II contains two well-characterized tyrosine radicals, D(.) and Z(.). Z is an electron carrier between the primary chlorophyll donor and the manganese catalytic site and is essential for enzymatic function. On the other hand, D forms a stable radical with no known role in oxygen evolution. D(.) and Z(.) give rise to similar, but not identical, room temperature electron paramagnetic resonance (EPR) signals, which can be distinguished by their decay kinetics. A third room temperature EPR signal has also been observed in site-directed mutants in which a nonredox active amino acid is substituted at the D or Z site. This four-line EPR signal has been shown to have a tyrosine origin by isotopic labeling (Boerner and Barry, 1994, J. Biol. Chem. 269:134-137), but such an EPR signal has never before been observed from a tyrosyl radical. The radical giving rise to this third unique signal has been named M+. Here we provide kinetic evidence that this signal arises from a third redox active tyrosine, distinct from tyrosine D and Z, in the photosystem II reaction center. Isotopic labeling and EPR spectroscopy provide evidence that M is a covalently modified tyrosine.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Ma C,Barry BAdoi
10.1016/S0006-3495(96)79394-3subject
Has Abstractpub_date
1996-10-01 00:00:00pages
1961-72issue
4eissn
0006-3495issn
1542-0086pii
S0006-3495(96)79394-3journal_volume
71pub_type
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