Abstract
When125Iwas given as an artificial electron donor to non‐O2‐evolving thylakoids of spinach, a 29 kDa polypeptide was specifically tagged by125I due to its photooxidation by PS II [(1985) Plant Cell Physiol. 26, 1093–1100]. We examined precisely the125I‐labeling pattern in comparison with azido[14C]atrazine photoaffinity labeling of D1 and immunoblotting with anti‐D1 and anti‐D2, and found that D1 (herbicidebinding protein) of PS II reaction center complex is specifically tagged by125I in three different species of higher plants (spinach, pea and wheat) and a thermophilic cyanobacterium (Synechococcus vulcanus). It was suggested that D1 bears the photooxidation site or has a domain very close to the photooxidation site on the donor side of PS II, in addition to the well established binding site for Qband herbicides on the acceptor side of PS II.

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