Microperoxidases: Structure, reactivity, and catalytic function of minimal haem-peptide systems

Understanding how surrounding proteins modify the intrinsic chemistry of haem centres is central to explaining haemoprotein function. Microperoxidases, minimal haem-peptide systems derived from cytochrome c, provide an experimentally accessible framework in which these contributions can be investigated under reduced structural constraints. This review synthesises more than five decades of research showing that many defining structural, electronic, redox, catalytic, and electron-transfer properties of haemoproteins are retained within a minimal haem-peptide scaffold. Dynamic coordination equilibria emerge as a central mechanistic principle governing ligand recognition, electronic structure, peroxide activation, high-valent intermediates, catalytic reactivity, electron transfer, supramolecular organisation, and responses to the local environment. These studies indicate that many fundamental features of haemoprotein chemistry arise from the intrinsic properties of the haem centre, while the surrounding molecular environment regulates this reactivity through coordination, steric organisation and control of molecular interactions. This understanding has established microperoxidases as powerful models for investigating haem chemistry and provided a rational basis for molecular engineering and functional applications. Challenges remain in catalyst stability, predictive molecular design, biological complexity, and practical translation, but microperoxidases continue to provide insight into the chemical principles governing haem reactivity in biological and synthetic systems.