The Asp-His-Fe triad of cytochrome c peroxidase controls the reduction potential, electronic structure, and coupling of the tryptophan free radical to the heme.

摘要: The buried charge of Asp-235 in cytochrome c peroxidase (CCP) forms an important hydrogen bond to the histidine ligand heme iron. Asp-His-metal interaction, which is similar catalytic triad serine proteases, found at active site many metalloenzymes and believed modulate character as a metal ligand. We have examined influence this interaction CCP on function, redox properties, iron zero-field splitting native ferric state its effect Trp-191 free radical oxidized ES complex. Unlike D235A D235N, mutation D235E introduces very little perturbation X-ray crystal structure enzyme site, with only minor changes geometry carboxylate-histidine no observable change site. More significant effects are observed position helix containing residue Glu-235. However, small all that necessary (1) increase reduction potential by 70 mV, (2) alter anisotropy EPR, (3) affect activity spin-state equilibrium, (4) reduce strength field measured splitting. substitution correlated splitting, suggesting control exerted through combination electrostatic effects. replacement Glu appears result significantly weaker proton resides essentially His-175. This nevertheless strong enough prevent reorientation conversion one two low-spin states for D235N. Asp-His-Fe therefore defining properties imidazolate His-175 has been proposed, yet most role function may be correctly orient efficient coupling maintain high-spin 5-coordinate center.