New approach to the construction of an artificial hemoprotein complex

Modified prosthetic metalloporphyrin, having a total of eight carboxylate groups at the terminal of two peripheral propionate side chains, was inserted into apomyoglobin to yield a new reconstituted myoglobin. The cluster of substituted carboxylates acts as the binding domain for cationic compounds such as methyl viologen and cytochrome c. Fluorescence spectroscopic analysis indicates that the reconstituted myoglobin formed a stable complex with methyl viologen and photoinduced singlet electron transfer (ET) occurred within the complex; k(et) = 2.1 x 10⁹ s^-1 and k(cr) = 3.3 x 10⁸ s^-1. Cytochrome c with a positively charged domain also interacted with the reconstituted myoglobin with an association constant of 6.5 x 10⁴ M^-1. The photoinduced triplet ET from the zinc reconstituted myoglobin to ferricytochrome c occurred through diprotein complex with a rate constant of 2.2 x 10³ s^-1. Furthermore, compared to native myoglobin, the ferryl state of the reconstituted myoglobin generated by hydrogen peroxide revealed the peroxidase activity with the acceleration of the oxidation of ferrocytochrome c via complex formation. The present approach could be very useful for constructing practical protein-protein complex systems to elucidate the biological ET via noncovalently linked biomolecules. (C) 1999 Elsevier Science S.A.