title: [125I]azido-ioxynil labels Val249 of the photosystem II D-1 reaction center protein.
abstract: Azido-ioxynil (3.5-diiodo-2-azido-4-hydroxy-benzonitrile) is a potent photosystem II inhibitor (pI50-value 7.38) and as effective as the parent compound ioxynil itself. [125I]azido-ioxynil exhibits specific binding to isolated thylakoids with a binding constant Kb = 7.14. Upon UV-illumination it binds covalently to thylakoids or photosystem II particles. It labels predominantly the 32 kDa D-1 photosystem II reaction center protein. A 41 kDa protein is only tagged in trace amounts. After proteolytic treatment of labeled D-1 protein with Staphylococcus aureus V8-protease two major and two minor fragments are obtained. Automated gas phase sequencing of a 7 kDa cleavage peptide revealed that Val249 is the primary target of azido-ioxynil binding. Compared to urea type herbicides, this places the ioxynil binding site in a different environment of the D-1 photosystem II protein.
authors.affiliation: Lehrstuhl Biochemie der Pflanzen, Ruhr-Universität, Bundesrepublik Deutschland.
authors.forename: W
authors.initials: W
authors.lastname: Oettmeier
authors.forename: K
authors.initials: K
authors.lastname: Masson
authors.forename: J
authors.initials: J
authors.lastname: Höhfeld
authors.forename: H E
authors.initials: HE
authors.lastname: Meyer
authors.forename: K
authors.initials: K
authors.lastname: Pfister
authors.forename: H P
authors.initials: HP
authors.lastname: Fischer
mesh_terms: D000595:Amino Acid Sequence; D001386:Azides / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism*; D006540:Herbicides / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D009570:Nitriles / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D001386:Azides; D006540:Herbicides; D007457:Iodine Radioisotopes; D045342:Light-Harvesting Protein Complexes; D009570:Nitriles; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C060804:azidoioxynil; D002734:Chlorophyll