Pheophytin

[3] In 1977, scientists Klevanik, Klimov, Shuvalov performed a series of experiments to demonstrate that it is pheophytin and not plastoquinone that serves as the primary electron acceptor in photosystem II.

Therefore, more experiments ensued to prove that pheophytin is indeed the primary electron acceptor of PSII, occurring between P680 and plastoquinone (Klimov, Allakhverdiev, Shuvalov).

The fifth and final step involves the filling of the “hole” in the special pair by an electron from a heme in cytochrome c. This regenerates the substrates and completes the cycle, allowing for subsequent reactions to take place.

Two negatively charged pheophytin radicals quickly pass their extra electrons to two consecutive plastoquinone molecules.

The reactions outlined above in the section concerning purple bacteria give a general illustration of the actual movement of the electrons through pheophytin and the photosystem.