Protoporphyrinogen IX oxidase

Pyraflufen-ethyl is also used as the defoliant for cotton and as a desiccant for potatoes. Pyraflufen-ethyl is a novel inhibitor of protoporphyrinogen IX oxidase. Inhibition of this enzyme in chloroplasts causes accumulation of protoporphyrinogen IX, which results in peroxidation of foliar cell membrane lipids under the light and finally death of cells. 

Uracil derivatives can also function as herbicides by inhibition of the enzyme protoporphyrinogen-IX-oxidase (PRO), which is involved in the biosynthesis of chlorophyll <2006H(68)561>. Commercial examples of such PPO inhibitors include isocil 1104, bromacil 1105, terbacil 1106, flupropacil 1107, lenacil 1108, butafenacil 1109, and benzfendizone 1110 (Figure 9). 

Figure 6. Binding site region of Protoporphyrinogen IX Oxidase 2 [Protox, pdb code ISEZ) with the co-crystallized inhibitor /NH (ball and sticks representation), the critical amino acid residue arginine (Arg) and the co-factor FAD. Re-docked solutions are indicated inside (int) and outside (ext) of the detected binding pocket.

Fig. 3.20. Protox inhibitor 4-bromo-3-(5-carboxy-4-chloro-2-fluorophenyl)-l-methyl-5-trifluoromethylpyrazole (79) used in protoporphyrinogen IX oxidase binding studies.

Carotenoid biosynthesis, acetolactate synthase (ALS) and protoporphyrinogen IX oxidase (PPO) for herbiddes. 

One relatively new herbicide is a pyrimidine-based chemical, salflufenacU (Kixor , BASF) [56]. This herbicide inhibits chlorophyll biosynthesis. In particular it inhibits protoporphyrinogen IX oxidase (PPO) in the tetrapyrrole biosynthetic pathway. Protoporphyrin IX is the heterocyUc ring system surrounding the magnesium cation in chlorophyll. There are several herbicides that operate by this mechanism. They are in group 14 (WSSA). 

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