DCMU

The reduction of a,a-difluoroacetophenone by a cyanobacterium proceeded both under light and in the dark, and the poor enantioselectivities (20-30% ee) observed in the dark were improved by irradiation. Thus, the enantioselectivities increased according to the lightness (70% ee under light (1000 lux)). The use of DCMU, a photosynthetic inhibitor, decreased the enantioselectivity of the reduction even under light conditions. The stereochemical course of the reduction is controlled by illumination or by adding DCMU. ... 

While phototactic action spectra measured in some Phormidium species indicate that chlorophyll a is not involved in the absorption of phototactically active light (see below), the phototactic action spectrum of Anabaena variabilis106) shows slight activity around 440 nm and a distinct peak at around 670 nm, both indicating chlorophyll a. Since blockers of the photosynthetic electron transport, such as DCMU andDBMIB, (see below) do not affect phototactic orientation, the active light seems not to be utilized via the photosynthetic electron transport chain (for further information see below). 

The action spectmm of positive and negative phototaxis of Anabaena variabilis was measured recently106). This species contains no C-phycoerythrin. Accordingly, maximum activity is found at around 615 nm (Fig. 7). In addition, in this form a second maximum occurs at around 675 nm, and a third small, but distinct, one at 440 nm, both indicating that chlorophyll a is also involved in the active light absorption (see above). The utilization via photosynthesis, however, could be excluded in this case, since the trichomes oriented themselves perfectly well to the light direction in the presence of photosynthetic inhibitors, such as DCMU and DBMIB, at concentrations in which the photosynthetic oxygen evolution was almost completely inhibited. 

Fig. 14. Inhibition of photophobic responses Rp by DCMU in the absence (closed circles) and presence (open circles) of an electric dc field of 0.83 V/cm. Abscissa DCMU concentration in mol Ordinate response in % of the uninhibited control (after Hader48))...

Synonyms AF 101 AI3-614378 Anduron Ansaron Bioron BRN 2215168 Caswell No. 410 CCRIS 1012 Cekiuron Crisuron Dailon DCMU DCMU 99 Dialer Dichlorfenidim 3-(3,4-Di-chlorophenol)-l,l-dimethylurea 3-(3,4-Dichlorophenyl)-l,l-dimethylurea A -(3,4-Dichloro-phenyl)-A,A-dimethylurea l,l-Dimethyl-3-(3,4-dichlorophenyl)urea Dion Direx 4L Diurex Diurol DMU DP hardener 95 Duran Durashield Dynex EINECS 206-354-4 EPA pesticide chemical code 035505 Farmco diuron Herbatox HW 920 Karmex Karmex diuron herbicide Karmex DW Krovar Lucenit Marmer NA 2767 NSC 8950 Seduron Sup r flo Telvar Telvar diuron weed killer UN 2767 Unidron Urox D USAF P-7 USAF XR-42 Vonduron. 

DCM, see Methylene chloride DCMU, see Diuron DCMU 99, see Diuron D-con, see Warfarin... 

Has sigma term probably corrects a Has small bi-linear component (7.) calculated log P. includes DCMU also. ... 

Piericidin A DCMU Competes with QB for binding site in PSII... 

DCMU is 3-(3,4-dichlorophenyl)-l,l-dimethylurea DCCD, dicyclohexylcarbodiimide FCCR cyanide-p-trifluoromethoxyphenylhydrazone DNR 2,4-dinitrophenol. 

Mode of Action of the Herbicide DCMU When chloroplasts are treated with 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU, or diuron), a potent herbicide, 02 evolution and photophosphorylation cease. Oxygen evolution, but not photophosphorylation, can be restored by addition of an external electron acceptor, or Hill reagent. How does DCMU act as a weed killer Suggest a location for the inhibitory action of this herbicide in the scheme shown in Figure 19-49. Explain. 

Figure 23-17 The zigzag scheme (Z scheme) for a two-quantum per electron photoreduction system of chloroplasts. Abbreviations are P680 and P700, reaction center chlorophylls Ph, pheophytin acceptor of electrons from PSII QA, Qg, quinones bound to reaction center proteins PQ, plastoquinone (mobile pool) Cyt, cytochromes PC, plastocyanin A0 and Aj, early electron acceptors for PSI, possibly chlorophyll and quinone, respectively Fx, Fe2S2 center bound to reaction center proteins FA, FB, Fe4S4 centers Fd, soluble ferredoxin and DCMU, dichlorophenyldimethylurea. Note that the positions of P682, P700, Ph, Qa/ Qb/ Ay and A, on the E° scale are uncertain. The E° values for P682 and P700 should be for the (chlorophyll / chlorophyll cation radical) pair in the reaction center environment. These may be lower than are shown.

The reagent DCMU specifically inhibits electron transfer to plastoquinone in photosystem II. Discuss how the administration of this compound to a suspension of illuminated chloroplasts will affect the production of oxygen, ATP, and NADPH. 

To investigate the influence of a photosynthesis inhibitor on the growth of the hairy roots, 0-10 mmol m 3 of 3-(3,4-dichlorophenyl)-l, 1-dimethylurea, DCMU, was supplemented in the medium according to the procedure described by Horn et al. [21]. The dishes were incubated in a chamber under the varied C02 concentrations of 0.03-8.5%. 

These suggest that the proliferation of the derived cell line of photoautotrophic pak-bung hairy roots is dependent entirely on photosynthesis for acquiring carbon and energy sources because DCMU blocks the reaction in photosynthetic process as shown in Fig. 6. In addition,based on the sensitive response to DCMU, a kind of photosynthesis inhibitor, the photoautotrophic hairy roots maybe used to detect some herbicides existing in the surroundings. 

Fig. 5. Influence of DCMU concentration on elongation rate of growing points of photo-autotrophic pak-bung hairy roots The hairy roots were cultivated in the sucrose-free medium using Petri dishes illuminated at 1= 11 W nr2, o photoautotrophic hairy roots, A heterotro-phic hairy roots...

Fig. 6. Sites of inhibitory action of DCMU in photosynthetic electron transport chain. The abbreviations are as follows - Cyt f cytochrome f, Fd ferredoxin, Mn water-splitting complex (manganese-containing), P680 pigment complex of photosystem II, P700 pigment complex of photosystem I, PC plastocyanin, PQ plastquinone, Q quencher, Rd NADP reductase and X direct electron acceptor complex...

Photosystem II. Spinach and pea PSII particles coated on different Ti02 based electrodes were used for photocurrent measurements in the presence of PSII electron acceptor DMBQ. In all experiments, addition of DMBQ resulted in an increase in photocurrent which remained constant for long periods. In control experiments with no deposition of PSII on the electrodes, there was no change in the photocurrent pattern on addition of DMBQ. Addition of the PSII oxygen evolution inhibitor DCMU caused an immediate fall in photocurrent, suggesting that the electron transport to the Ti02 electrode is linked to water photolysis. 

Answer DCMU must inhibit the electron-transfer system linking photosystem II and photosystem I at a position ahead of the first site of ATP production. DCMU competes with PQB for electrons from PQA (Table 19-4). Addition of a Hill reagent allows H20 to be split and 02 to be evolved, but electrons are pulled out of the system before the point of ATP synthesis and before the production of NADPH. DCMU kills plants by inhibiting ATP production. 

Fig. 4 Dynamics of in vivo chlorophyll fluorescence (Fo) and photosynthetic efficiency (Fv/Fm) of Phaeocystis globosa during viral infection as assessed by fluorometry. Open symbols represent uninfected cultures, while the filled symbols represent virally infected P. globosa. Maximum fluorescence (Fm) was obtained after addition of the photosystem II inhibitor DCMU (20 pM final concentration). Fv equals Fm-Fo. Data are expressed in relative units (r.u.)...

Fortunately, the electron-acceptor side of PSII can be exploited to allow turnover control of the S states in highly concentrated samples. A number of herbicides are known that bind tightly to the QB site and block electron transfer past the primary quinone electron acceptor (QA) (13). Some examples are shown in Figure 3. Equations 4 and 5 show the reactions of PSII in the presence of 3-(3,4-dichlorophenyl)-l,l-di-methylurea (DCMU, Figure 3). 

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. 

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