Herbicide binding

Photosystem II inhibitors, 13 288-294 plant growth regulator synthesis and function inhibitors, 13 304—307 Herbicide analysis methods, 13 312—313 Herbicide atomizer, 23 197 Herbicide binding, polypeptide... 

Heptagold heteronuclear cluster compounds X-ray crystallography, 39 371-373 Heptasulfur imide, 2 161-164 Herbicide-binding protein, 33 224 Heteroallenes, cycloaddition to iminoboianes, 31 161... 

Still the identity, nature, and size of the herbicide-binding protein remained a puzzle. This putative protein was likely very hydrophobic. A methodology for isolating such membrane proteins was not at that time available. Even more difficult to comprehend was the orientation of such hydrophobic proteins in a membrane that had been a matter of discussion for many decades. The first X-ray structure of a membrane protein complex in 1985 suddenly solved this orientation question, as will be discussed below. 

The Three-Dimensional Orientation of the Triazines in the Herbicide-Binding Protein of PS II... 

Figure 8.2 Folding of the amino acid sequence of the herbicide-binding niche in the D1 protein of PS II.

Significance of the Rapid Turnover of the Herbicide-Binding Protein for the Mode of Action of Triazines 107... 

Erickson, J.M., M. Rahire, J.D. Rochaix, and L. Mets (1985). Herbicide resistance and cross-resistance Changes at three distinct sites in the herbicide-binding protein. Science, 228 204-207. 

Johanningmeier, U., U. Bodner, and G.F. Wildner (1987). A new mutation in the gene coding for the herbicide-binding protein in Chlamydomonas. Fed. European Biochem. Societies Lett., 211 221-224. 

Pfister, K., S.R. Radosevich, and C.J. Arntzen (1979). Modification of herbicide binding to photosystem II in two biotypes of Senecio vulgaris L. Plant Physiol. 64 995-999. 

Sinning, I. (1992). Herbicide binding in the bacterial photosynthetic reaction center. Trends Biochem. Sci., 17 150-154. 

Trebst, A. (1986). The topology of the plastoquinone and herbicide binding peptides of photosystem II in the thylakoid membrane. Z Naturforsch. Sect. C Biosci., 41 240-245. 

Trebst, A. (1987). The three dimensional structure of the herbicide binding niche on the reaction center polypeptide of photosystem II. 

Vermass, W.F.J. and C.J. Arntzen (1984). Synthetic quinones influencing herbicide binding and photosystem II electron transport. The effects of triazine-resistance on quinone binding properties in thylakoid membranes. Biochim. Biophys. Acta., 725 483 -91. 

Triazines are selective herbicides used to control a wide spectrum of grass and broadleaf weeds in cereal, oilseed, and horticultural crops. Triazine herbicides kill weeds by interfering with the electron transport chain in photosystem II (PS II). These herbicides bind to the QB protein in the PS II reaction center and block the flow of electrons through the photosynthetic electron transport chain. 

Triazine (e.g., atrazine, simazine) and substituted urea (e.g., diuron, monuron) herbicides bind to the plastoquinone (PQ)-binding site on the D1 protein in the PS II reaction center of the photosynthetic electron transport chain. This blocks the transfer of electrons from the electron donor, QA, to the mobile electron carrier, QB. The resultant inhibition of electron transport has two major consequences (i) a shortage of reduced nicotinamide adenine dinucleotide phosphate (NADP+), which is required for C02 fixation and (ii) the formation of oxygen radicals (H202, OH, etc.), which cause photooxidation of important molecules in the chloroplast (e.g., chlorophylls, unsaturated lipids, etc.). The latter is the major herbicidal consequence of the inhibition of photosynthetic electron transport. 

The high efficacy of triazine herbicides and their repetitive use in crops and noncrop situations has resulted in the selection of weeds that are resistant to these herbicides or are not well controlled at the lower rates now being used. In most instances, triazine resistance is due to an alteration in the herbicide-binding site in PS II. Despite the widespread occurrence of triazine resistance, these herbicides are still widely used, even in fields in which triazine-resistant biotypes are known to occur. The rate of increase in the selection for triazine-resistant weed species depends in part on the integration of alternative weed control strategies, in addition to the use of triazine herbicides, for control of these weed species. Due to their resistance mechanism, many triazine-resistant weeds are less competitive than their susceptible counterparts. 

Bowes, J., A.R. Crofts, and C.J. Arntzen (1980). Redox reactions on the reducing side of photosystem II in chloroplast with altered herbicide binding properties. Arch. Biochem. Biophys., 200 303-308. 

Smeda, R.J., PM. Hasegawa, P.B. Goldsbrough, N.K. Singh, and S.C. Weller (1993). A serine-to-threonine substitution in the triazine herbicide-binding protein in potato cells results in atrazine resistance without impairing productivity. Plant Physiol., 103 911-917. 

Herbicides that inhibit photosynthetic electron flow prevent reduction of plastoquinone by the photosystem II acceptor complex. The properties of the photosystem II herbicide receptor proteins have been investigated by binding and displacement studies with radiolabeled herbicides. The herbicide receptor proteins have been identified with herbicide-derived photoaffinity labels. Herbicides, similar in their mode of action to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) bind to a 34 kDa protein, whereas phenolic herbicides bind to the 43-51 kDa photosystem II reaction center proteins. At these receptor proteins, plastoquinone/herbicide interactions and plastoquinone binding sites have been studied, the latter by means of a plastoquinone-deriv-ed photoaffinity label. For the 34 kDa herbicide binding protein, whose amino acid sequence is known, herbicide and plastoquinone binding are discussed at the molecular level. 

It was originally assumed that the herbicides bind to a protein component of photosystem II (named "B" or R") ( 1, 2J. This protein component was assumed to contain a special bound plastoquinone whose midpoint potential is lowered due to herbicide binding. Consequently, electron flow is interrupted ( 1,2). The photosystem II... 

In 1979, the concept of a photosystem II herbicide binding protein with different but overlapping binding sites for the various photosystem II herbicides was simultaneously established by Trebst and Draber ( 5) and Pfister and Arntzen (6). This idea of a herbicide receptor protein proved to be extremely fruitful because the techniques of receptor biochemistry were now applicable. Tischer and Strotmann (7) were the first investigators to study binding of radiolabeled herbicides in isolated thylakoids. 

Tischer and Strotmann ( 7), the binding constant corresponds to the inhibition constant, i. e. the I,. value (the concentration necessary for 50% inhibition of photosynthetic electron transport), provided the I. value is extrapolated to zero chlorophyll concentration. The value of 527 molecules of chlorophyll per molecule of bound inhibitor indicates that roughly one molecule of herbicide binds per electron transport chain, because about 400-600 molecules of chlorophyll are considered to be associated with each electron transport chain. 

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