Alkylamine-Ligated H93G Myoglobin Cavity Mutant: A Model System for Endogenous Lysine and Terminal Amine Ligation in Heme Proteins such as Nitrite Reductase and Cytochrome f

TLDR: This study has successfully generated and spectroscopically characterized the H93G Mb cavity mutant ligated with less common alkylamine ligands (models for Lys or the amine group of N-terminal amino acids) in numerous heme iron states, the first systematic spectral study of models for alkyamine- or terminal amine-ligated heme centers in proteins.

Abstract: His93Gly sperm whale myoglobin (H93G Mb) has the proximal histidine ligand removed to create a cavity for exogenous ligand binding, providing a remarkably versatile template for the preparation of model heme complexes The investigation of model heme adducts is an important way to probe the relationship between coordination structure and catalytic function in heme enzymes In this study, we have successfully generated and spectroscopically characterized the H93G Mb cavity mutant ligated with less common alkylamine ligands (models for Lys or the amine group of N-terminal amino acids) in numerous heme iron states All complexes have been characterized by electronic absorption and magnetic circular dichroism spectroscopy in comparison with data for parallel imidazole-ligated H93G heme iron moieties This is the first systematic spectral study of models for alkylamine- or terminal amine-ligated heme centers in proteins High-spin mono- and low-spin bis-amine-ligated ferrous and ferric H93G Mb adducts have been prepared together with mixed-ligand ferric heme complexes with alkylamine trans to nitrite or imidazole as heme coordination models for cytochrome c nitrite reductase or cytochrome f, respectively Six-coordinate ferrous H93G Mb derivatives with CO, NO, and O(2) trans to the alkylamine have also been successfully formed, the latter for the first time Finally, a novel high-valent ferryl species has been generated The data in this study represent the first thorough investigation of the spectroscopic properties of alkylamine-ligated heme iron systems as models for naturally occurring heme proteins ligated by Lys or terminal amines