Ligand binding properties of two kinds of reconstituted myoglobins with iron porphycene having propionates: Effect of β-pyrrolic position of two propionate side chains in porphycene framework

An iron porphycene containing two propionate side chains at the 12th and 17th β-pyrrolic positions of the porphycene ring was synthesized and incorporated into sperm whale apomyoglobin in order to investigate the O2 and CO binding properties of the reconstituted ferrous myoglobin. The protein showed a slower O2 dissociation rate by 1/20, compared to the native myoglobin, whereas the CO dissociation rates were found to be almost the same. This tendency is similar to the result of a previous study on the reconstituted myoglobin with a porphycene having the propionates at the 13th and 16th β-pyrrolic positions. However, the present myoglobin showed a faster O2 dissociation than the previously studied myoglobin. This finding suggests that the position of the two propionates as well as the symmetry of the porphycene framework is an important factor for obtaining a stable oxygenated iron porphycene myoglobin.