Non-covalent modification of the heme-pocket of apomyoglobin by a 1,10-phenanthroline derivative

To expand the repertoire of artificial enzymes that are constructed by replacing the natural prosthetic group of hemoproteins with non-natural cofactors, we examined incorporation of a non-porphyrinic ligand (1) into the heme-pocket of apomyoglobin in a non-covalent fashion. Ligand 1 is a highly conjugated 1,10-phenanthroline derivative, which shares some structural features with protoporphyrin IX; for example, molecular size and arrangement of hydrophobic and anionic parts. Addition of apomyoglobin to a solution of 1 induces clear changes in the absorption spectrum of 1, suggesting one-to-one incorporation of 1 into the heme cavity of apomyoglobin with an affinity of 6.3 × 106 M−1. We found that the hydrolytic activity of apomyoglobin toward p-nitrophenyl hexanoate was greatly suppressed because of the incorporation of 1 into the heme-pocket.

Graphical abstractTo expand the repertoire of artificial enzymes constructed by replacement of prosthetic groups of hemoproteins, we examined incorporation of a non-porphyrinic ligand, a water-soluble 1,10-phenanthroline derivative (1), into the heme-pocket of apomyoglobin. Strong incorporation of 1 into the heme cavity of apomyoglobin greatly suppresses the hydrolytic activity of apomyoglobin toward p-nitrophenyl hexanoate.Figure optionsDownload full-size imageDownload as PowerPoint slide