In photosystem-I, the primary electron acceptor is probable a Fe-S protein. The reduced primary acceptor transfers the electrons to secondary electron acceptor (most probable \(P_{430}\)). The sequence of electron transfer is as follows:
\(\underset{\left(\text {chl}\left.-a^{+}\right)\right.}{P_{700}} \xrightarrow{e^{-}} \underset{(\text {Phyloquinone})}{A_1} \xrightarrow{e^{-}} \underset{(\text {Fe-S protein})}{A_2} \xrightarrow{e^{-}} \underset{\left(P_{430}\right)}{A_3}\)
The reduced \(P_{430}\) passess its electrons to ferredoxin (Fd) present at outer surface of thylakoid membrane.