Ligand photodissociation and recombination dynamics of ferrous cytochrome c peroxidase at alkaline pH

The dynamics associated with ligand photodissociation and ligand binding provide an avenue through which information concerning conformational interactions involving the active site of heme proteins may be obtained. To date, most time-resolved spectroscopic investigations have involved exogenous π-acceptor ligands such as CO, O_2, and NO. In fact, until very recently hexacoordinate low-spin hemes with strong-field σ-donor ligands were considered to be largely nonphotolabile. Magda and coworkers have, however, demonstrated that both cytochrome c and cytochrome b_5 exhibit photodissociation of nitrogenous ligands on a very fast (< 100 ps) time scale. Photodissociation of a σ ligand has also been implicated in the photodynamics of the cytochrome a_3 distal heme pocket in cytochrome c oxidase. This study characterizes the dynamics of the low-spin alkaline form of ferrous cytochrome c peroxidase (CCP) subsequent to heme photodissociation