Identification of a 32-34-kilodalton polypeptide as a herbicide receptor protein in Photosystem II

Photosystem II particles which retained high rates of herbicide-sensitive activity were used to examine the site(s) of action of various herbicides. A polypeptide of 32-34 kdaltons was identified as the triazine-herbicide binding site based upon: (a) parallel loss of atrazine activity and the polypeptide during either trypsin treatment or selective detergent depletion of protein in the Photosystem II complex, and (b) covalent labeling of the polypeptide by a ¹⁴C-labeled photoaffinity triazine. In Photosystem II particles depleted of the 32-34-kdalton polypeptide, electron transport was still active and was slightly sensitive to DCMU and largely sensitive to dinoseb (urea and nitrophenol herbicides, respectively). On the basis of this result it is proposed that the general herbicide binding site common to atrazine, DCMU and dinoseb is formed by a minimum of two polypeptides which determine affinity and/or mediate herbicide-induced inhibition of electron transport on the acceptor side of Photosystem II.