It was reported that the substrate-bound of the human ferrochelatase possesses a “closed” active site conformation while the substrate-free enzyme has an “open” active site,which may regulate protoporphyrin binding and product release,and the π-helix(340-349)was observed at unwound state in the F110A variant enzyme of bound heme.What leads the enzyme to change active site conformation,which residues are involved in the substrate entering and exiting the active site pocket and why the conformation of the π-helix changes when ferrous ion is imported? To answer these questions,molecular dynamics(MD)simulations of the three models based on the crystal structure E343K were performed.The open and closed conformations of the enzyme obtained by simulation are in agreement with the corresponding crystal structures.The snapshots and the structure analysis indicate that the alteration of the hydrogen bond and position of E347 and E351 lead to the conformational change of the π-helix.The reorientations of the residues F337,H341 and E343 have no effect on the π-helix.Instead,F337 acts as a door that alternatively opens and closes the entrances to two solvent-filled tunnels located at H263 and H341.The movement of the residues 90-115 leads to the conformation change of the enzyme between open and closed state.The residue R164 acts as a signal showing the alteration of the active site conformation.When R164 forms hydrogen bond with D95,the active site is closed,and hydrogen bond with E171,the active site is open.Interestingly,the pophyrin with Fe2+ was observerd to move largely toward out of the enzyme while the pophyrin without Fe2+ almost keep fixed.The alteration of the hydrogen bonds between the propionate of the heme with R115,K118 and S303 trigger the movement of heme out of the active site.And the residues E347 and E351 locating on the π-helix,which form an acidic path leading a salt bridge interaction with the propionate of the heme,accelerate the release process.