Herbicide binding specific

The phenolic photoaffinity label azidodinoseb (Figure 4) binds less specifically than either azidoatrazine or azidotriazinone (14). In addition to other proteins, it labels predominantly the photosystem II reaction center proteins (spinach 43 and 47 kDa Chlamydomo-nas 47 and 51 kDa) (17). Because of the unspecific binding of azidodinoseb, this can best be seen in photosystem II preparations (17). Thus, the phenolic herbicides bind predominantly to the photosystem II reaction center, which might explain many of the differences observed between "DCMU-type" and phenolic herbicides (9). The photosystem II reaction center proteins and the 34 kDa herbicide binding protein must be located closely to and interact with each other in order to explain the mutual displacement of both types of herbicides (8,12,21). Furthermore, it should be noted that for phenolic herbicides, some effects at the donor side of photosystem II (22) and on carotenoid oxidation in the photosystem II reaction center have been found (23). 

Iodolabeling studies on photosystem II particles from higher plants and cyanobacteria (221) and on a PSII complex (227) specifically labeled the herbicide-binding protein. As 1 is believed to donate electrons to Z, the secondary electron donor which is believed to accept electrons from the photosynthetic manganese complex, these experiments indicate a role for this protein on the oxidizing side of PSII. Consequently, Z must at least be located near, if not in, the herbicidebinding polypeptide (222). 

Environmental pollution by toxic chemicals has become one of the worlds most serious problems. Among the most widespread pesticides is photosynthesis inhibiting herbicides, such as atrazine, metribuzin, diuron, bromacil, ioxynil and dinoseb. They all beloi to different families but have a common mode of action binding specifically to the chloroplast D1 protein with subsequent intetmption of the electron and proton flow through Photosystem II. The goal of this chapter is to evaluate the possibility of application of the natural receptor properties of D1 protein in various biosensor systems for herbicide detection. 

Great attention has been paid to the application of thylakoid membranes and photosynthetic microorganisms in environmental pollution control. The biorecognition system based on the binding of certain herbicides to the photosynthetic reaction center of plants and microorganisms seems to be the most direa and simple method for herbicide detection. These systems used as sensor s recognition elements allow the detection of a broad range of herbicides. Unfortunately, their stability and sensitivity are insufficient in the most cases. From this point of view, the DI protein, which binds specifically... 

The specificity of the whole cells and isolated photosynthetic materials was obtained by applyir the knowledge available on the relationships between herbicide binding activity and the structure of the D1 protein. For example, distinctions among classes of chemicals could be achieved through mutations in amino acid residues of D1 which can impart resistance to individual triazine herbicides. Realisation of new, sophisticated transduction systems based on printed electrodes, fluorescence and chemiluminescence as well as alternative systems such as the reconstimtion of Qp site in overexpressed DI protein utilizing chromophore quinones to enhance sensitivity and specificity for detected signals. 

In a recent theoretical study, Shipman (36) proposed several specific models for the herbicide binding site on PS II. It was proposed that the PS II herbicides bind electrostatically at or near a protein salt bridge or the terminus of an alpha helix. 

Herbicide Binding Assays. Control and trypsin-treated chloroplast thylakoids were suspended in PSNM buffer. Buffer (1 ml volume) containing 50 Chi was incubated 3 min with l C-atrazine (specific activity 27.2 pCi/mg). Chloroplasts were pelleted and an aliquot of the supernatant was removed for determination of the amount of unbound atrazine. Details of this procedure are described elsewhere (6, 9). Radiolabeled atrazine was a gift of Dr. H. LeBaron, CTBA-GEIGY, N. Carolina. 

Our results on inhibition of herbicide binding activity agree with the involvement of the Qb site in photoinhibition. In fact the binding curves correlates with the loss of electron transport activity in the first 30 min. The best correlation was observed with the herbicide loxynil. Atrazine and Dinoseb showed a residual binding even when Di protein was not detectable by immunoblotting (data not shown) indicating non-specific binding or the involvement of other proteins in their association with thylakoids. This is in accordance with previous observations (3). 

In addition to attempting to identify the exact sites of interaction of herbicides with specific amino acids, other workers have stressed the importance of an association with thylakoid lipids, and also the specific structure of plastoquinone. It is well known that PSII herbicides compete with Qb for its binding site and thus, by displacing the quinone, inhibit electron... 

It is not inconceivable that such permeability effects are a result of an initial direct effect of herbicide binding to ATPase or an electron transport chain component and/or a protonophore action. However, most, if not all, the herbicides discussed in this section can be classed as multisite inhibitors as evidenced by their inclusion in previous chapters, particularly Chapter 1, and elsewhere in this chapter. Such a membrane partitioning would not be specific to the inner mitochondrial membrane but would occur in other... 

Triazines inhibit photosynthesis in all organisms with oxygen-evolving photosystems. They block photosynthetic electron transport by displacing plastoquinone from a specific-binding site on the D1 protein subunit of photosystem II (PS II). This mode of action is shared with several structurally different groups of other herbicides. The elucidation of the mechanism of the inhibitory action is followed in this review. 

As part of SW-846, the EPA has validated and approved many immunoassay and colorimetric screening methods for a wide range of contaminants, such as petroleum fuels, pesticides, herbicides, PCBs, and explosives. Immunoassay technology uses the property of antibodies to bind to specific classes of environmental pollutants allowing fast and sensitive semiquantitative or qualitative detection. Colorimetric kits are based on the use of chemical reactions that indicate the presence of target analytes by a change in color. Table 3.9 presents a summary of EPA-approved screening methods and their detection capabilities. 

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