Doctors Gray and Winkler of CalTech will investigate the photochemistry of modified metalloenzymes with support from the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division and the Biophysics Program of the Molecular and Biochemical Sciences Division. These workers will combine methods and systems from inorganic chemistry, physical chemistry, and molecular biology to custom design light-driven multielectron redox enzymes. They will photoinitiate single-electron-transfer reactions that will result in formation of oxo-iron (ferryl) species in variants of cytochrome c and myoglobin. These proteins will be tailored for ferryl formation by use of semisynthetic and site-directed mutagenesis techniques. Histidine residues for ruthenium binding will be introduced at surface sites on the proteins, and alterations in the protein heme environments will adapt the protein to support ferryl species in the active sites. Upon photolysis, electron transfer between the ruthemium and heme moieties will lead to ferryl formation. %%% An important intermediate species in many reactions of dioxygen that are catalyzed by heme proteins is one that contains the iron atom of the heme bound to an oxygen atom. These "ferryl" species in the past have proven difficult to characterize because of their high reactivity. A novel and powerful method to generate and detect them will be developed that depends first on using methods of molecular biology to engineer the proteins so as to facilitate electron transfer reactions that can be driven by a short flash of laser light. The ferryl species will then be detected by use of their optical properties, and information on their reactivity will be obtained directly.
