Spectroscopic Studies of Blue Copper and Iron Sulfur Electron Transfer Active Sites

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Professor Solomon of Stanford University will conduct studies on metal-containing active sites which have unique spectral features relative to small molecule complexes of the same ion. The general goal is to understand these features in terms of the active site geometric and electronic structural contributions to the reactivity of these sites in biology. The proteins of interest are the blue copper and iron-sulfur centers which occur in biological electron transfer. The unique spectral features of these systems in their natural state reflect novel electronic structures which affect the reduction potentials and the kinetics of electron transfer. Specifically, the studies are directed at `perturbed` blue copper sites which occur naturally or in mutated proteins and have significant spectral and reactivity differences relative to classic blue copper sites, and at a thorough understanding of the complete orbital pathway for electron coupling over the blue copper-Cys-His-Type 2 (or Type 3) unit involved in intramolecular electron transfer in nitrite reductase and the multicopper oxidases. The iron-sulfur studies will focus on the contribution of the electronics to the redox properties of the rubredoxin iron-sulfur center, and extension to 2- and 4-iron sulfur centers and to heterometal clusters. The ultimate goal in these studies is to experimentally determine the changes in electronic structure associated with coupling to additional metal centers and to understand the contributions of electron delocalization to the reduction potentials and electron transfer reactivity. A diverse array of sophisticated spectroscopic techniques will be used to learn about the bonding at the active sites of two classes of metal-containing proteins. These proteins contain either copper-sulfur or iron-sulfur centers, are found in most organisms, and function in the physiological electron transport chains. The approach to be taken will entail detailed experimental and theoretical study of simple models of the active sites, as well as experimental study of a series of modified copper proteins. The information obtained will lead to an understanding of how the bonding at the metal sites controls the rates and energetics of reactions of these proteins.