Slipping of a histidine improved the peroxidase activity of a de novo designed polypeptide packing an iron porphyrin

Polypeptides with two histidines and an iron porphyrin () were synthesized with a variety of positions of a histidine. In , histidine (H43) was in the hydrophobic region of an α-helix. The other polypeptides were of slightly or substantially distorted conformation. In the pH 7.2 buffer solution, two histidines of the polypeptide coordinated the iron porphyrin regardless of their positions. Some polypeptides (, , and ) showed an enhanced catalytic activity in the peroxidase reaction using cumene hydroperoxide compared to that of , whereas some polypeptides ( and ) were ineffective catalysts. The distortion of the peptide conformation by the addition of MeOH was also effective for the peroxidase reaction.