Date of Award
Doctor of Philosophy
Nenad M. Kostic
Electron-transfer reactions are essential for life. Because metalloproteins are involved in electron transport in the cell, it is important to understand the factors that affect recognition, interaction, and reactions of these electron carriers. Cytochrome c is well-characterized electron-carrier protein. The heme protein cytochrome c and the blue-copper protein plastocyanin are well suited for kinetic and mechanistic studies since their structures are known in detail;We investigated the effects of site-directed mutations and viscosity on rate-limiting rearrangement within the complex of cytochrome c and plastocyanin and identified the reactive configuration of the complex. In the reactive configuration of the complex cytochrome c heme edge is between plastocyanin acidic and hydrophobic patch. The reactive intermediate is formed upon transfer of an electron in the reaction of cytochrome c and plastocyanin. The intermediate is zinc cytochrome c cation radical which exhibits different reactivity from the native iron(III) form of the protein. The reorganization energy and electron self-exchange rate constant of the zinc cytochrome c cation radical show that methionine, ligand in iron form of the protein, is uncoordinated in the zinc form of the protein;We extended the proton-linkage model so it can give information about individual proteins and even about amino-acid residues involved in protein association. We extract from the experimental results the composite pK a values, both in separate and in combined proteins, of groups of residues that change their protonation state upon protein association. The extended model was applied to intricate effects of pH on association of cytochrome c with wild-type and several mutant forms of plastocyanin. We extract from the experimental results the composite pKa values, both in separate and in combined proteins, of groups of residues that change their protonation state upon protein association. Interpretation of these parameters revealed general and specific features of the protein-protein interaction;The effects of pH on protein rearrangement were studied. The rearrangement is independent of pH and amino acid side chains in the acidic patch of plastocyanin are deprotonated in the complex of cytochrome c and plastocyanin. Study of effects of pH on a dynamic protein complex allows inferences about the protonation states of particular side chains.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Milan Miroslav Crnogorac
Crnogorac, Milan Miroslav, "Interactions and electron-transfer reactions between metalloproteins " (2000). Retrospective Theses and Dissertations. 13893.