Multi-Frequency Electron Paramagnetic Resonance Studies on Iron-Sulfur Proteins, Photosystem II, and Selenocysteine Azurin

Multi-frequency electron paramagnetic resonance (EPR) methods were used to investigate the local environment around the paramagnetic site of three types of redox active metalloproteins; the mitochondrial human protein MitoNEET (and a Rieske center), the photosynthetic component Photosystem II, and a selenocysteine-substituted mutant of azurin. In addition to X-band (≈ 9GHz) and Q-band (≈ 34 GHz) instrumentation commonly used in such studies, a home-built Ka-band (≈ 31 GHz) pulsed EPR spectrometer assisted in the determination of EPR parameters for the mitoNEET protein. The hardware and software design of the Ka-band instrument will be discussed in detail in this dissertation, as well as, modifications designed to upgrade the pulse programming component of the this spectrometer.;Success in determining an accurate full set of EPR parameters for the Ndelta of the singly bound histidine ligand to the redox active [2Fe-2S] cluster for both 14N and globally labeled 15N mitoNEET preparations was accomplished by simultaneously simulating over multi-frequency and mult-technique experiments including Continuous Wave (CW), Electron Spin Echo Envelope Modulation (ESEEM), Electron Double Nuclear Resonance (ENDOR), and Hyperfine Sublevel Correlation (HYSCORE) methods. MitoNEET served as a model for preliminary studies on the more complicated system, Thermus thermophilus Rieske protein.;Advanced EPR methods were applied to study S2-State water substrate interactions with the Mn4Ox Ca cluster in the Photosystem II component of photosynthesis using isotopically exchanged H217O. Combined with computer simulations, Q-band ESEEM method detection gave rise to signals that are interpreted as evidence for direct water ligation of at least one substrate H2 17O molecule.