DCMU inhibits the electron transfer system in thylakoid membranes by targeting photosystem II (PSII). Specifically, it binds to the QB site of the D1 protein in PSII, preventing the transfer of electrons to plastoquinone. This leads to photoinhibition and blocks the flow of electrons from water to plastoquinone in the light reactions of photosynthesis.

DCMU Interferes with Pastoquinone-Protein Interactions Blocking Reduction of Pastoquinone and Subsequent Redox Reactions.