Haem peptide–protein interactions. Part 2. — Kinetics and mechanism of the interaction of microperoxides-8 with apomyoglobin

Abstract

The kinetics of the interaction between the haem octapeptide micro-peroxidase-8 (MP-8) and apomyoglobin (_apoMb) have been investigated as a model for the reaction of monomeric ferriproporphyrin IX (haemin) as a model for the reactio of monomeric ferriproporphyrin IX (haemin) with apohaemoproteins. The kinetics of the reaction are consistent with a two-stage sige-intermediate interaction process. Close agreement between the association constant calculated using microscopic rate constants, and that measured by spectrophotometric titration provides powerful positiv eevidence for the correctness of the proposed mechanism. On the basis of the kinetic binidng studie sand spectrophotometric observation of the reduction of the Fe³⁺MP-8 ·_apoMB complex we propose a novel equilibrium between a bis - and mono-axially histidyl ligated iron species for the peptide–protein complex in solution.