Transient photoligation behavior of nickel protoporphyrin reconstituted myoglobin and hemoglobin

The transient photoligation behavior of nickel protoporphyrin IX (NI(PP)) in a variety of local environments has been studied by time-resolved resonance Raman scattering. In coordinating basic solvents the ligation changes engendered by the photoexcitation of a net d/sup 2//sub z/sup 2// ..-->.. d/sup 1//sub x/sup 2/-y/sup 2//, d/sup 1//sub z/sup 2// (/sup 1/A/sub 1g/ ..-->.. /sup 3/B/sub 1g/) transition are easily monitored by changes in Ni(PP) Raman modes that are sensitive to metalloporphyrin spin-state and ligation changes. The photodynamics exhibited by Ni(PP) incorporated into Mb or Hb apoproteins or into detergent micelles are distinct from those of Ni(PP) in coordinating solvents and from each other. The equilibrium 4-coordinate Ni(PP) sites in NiHb display a transient photoassociation of a single ligand similar to the behavior of Ni(PP) in solution. The photodynamics of the equilibrium 5-coordinate Ni(PP) sites in NiHb and NiMb are, however, greatly modulated by the surrounding protein matrix.