3-(3,4-Dichlorophenyl)-1,1-dimethylurea, Karmex, Diuron, Direx
3D model (JSmol)
|UN number||3077, 2767|
CompTox Dashboard (EPA)
|Molar mass||233.09 g·mol−1|
|Appearance||white crystalline solid|
|Melting point||158 °C (316 °F; 431 K)|
|Boiling point||180 °C (356 °F; 453 K)|
|Vapor pressure||0.000000002 mmHg (20°C)|
|GHS Signal word||Warning|
|H302, H351, H373, H400, H410|
|P201, P202, P260, P264, P270, P273, P281, P301+312, P308+313, P314, P330, P391, P405, P501|
|Flash point||noncombustible |
|NIOSH (US health exposure limits):|
|TWA 10 mg/m3|
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Mechanism of action
DCMU is a very specific and sensitive inhibitor of photosynthesis. It blocks the QB plastoquinone binding site of photosystem II, disallowing the electron flow from photosystem II to plastoquinone. This interrupts the photosynthetic electron transport chain in photosynthesis and thus reduces the ability of the plant to turn light energy into chemical energy (ATP and reductant potential).
DCMU only blocks electron flow from photosystem II, it has no effect on photosystem I or other reactions in photosynthesis, such as light absorption or carbon fixation in the Calvin cycle.
However, because it blocks electrons produced from water oxidation in PS II from entering the plastoquinone pool, "linear" photosynthesis is effectively shut down, as there are no available electrons to exit the photosynthetic electron flow cycle for reduction of NADP+ to NADPH. In fact, it was found that DCMU not only does not inhibit the cyclic photosynthetic pathway, but, under certain circumstances, actually stimulates it.
Because of these effects, DCMU is often used to study energy flow in photosynthesis.
- NIOSH Pocket Guide to Chemical Hazards. "#0247". National Institute for Occupational Safety and Health (NIOSH).
- Metz, J; Pakrasi, H; Seibert, M; Arntzer, C (1986). "Evidence for a dual function of the herbicide-binding D1 protein in photosystem II". FEBS Letters. 205 (2): 269. doi:10.1016/0014-5793(86)80911-5.
- HUBER, S.C. EDWARDS, G.E. (1976), Studies on the Pathway of Cyclic Electron Flow in Mesophyll Chloroplasts of a C4 Plant, Biochimica et Biophysica Acta (BBA) - Bioenergetics, Volume 449, Issue 3, 6 December 1976, Pages 420-433, doi:10.1016/0005-2728(76)90153-5
- Hosler, J. P.; Yocum, C. F. (April 1987). "Regulation of Cyclic Photophosphorylation during Ferredoxin-Mediated Electron Transport : Effect of DCMU and the NADPH/NADP Ratio". Plant Physiol. 83 (4): 965–9. doi:10.1104/pp.83.4.965. PMC 1056483. PMID 16665372.