The aim of the proposed work is to use a combination of structural, biochemical and genetic approaches to study structure/function relationships in flavoproteins. The work will focus on two structurally homologous FAD-containing enzymes, putidaredoxin reductase from Pseudomonas putida and apoptosis inducing factor from mice. Putidaredoxin reductase catalyzes electron transfer from NADH to an iron-sulfur protein, putidaredoxin, in cytochrome P450cam monooxygenase. The mechanism of complex formation and electron transfer between putidaredoxin reductase and putidaredoxin is not well understood. We have recently demonstrated that putidaredoxin reductase has redox active cysteines and can function as dithiol/disulfide oxidoreductase. Since there are no putative disulfide redox centers encoded by CysXXCys or CysXXXXCys motifs characteristic for traditional disulfide reductases, the mechanism of dithiol/disulfide oxidoreduction catalyzed by putidaredoxin reductase seems to be unique and needs to be elucidated. Apoptosis inducing factor is a phylogenetically old mammalian, caspase-independent death effector which, upon apoptosis induction, translocates from its normal localization, the mitochondrial intermembrane space, to the nucleus where it causes chromatin condensation and DNA fragmentation. Neither physiological function nor mechanism of apoptosis induced by this protein is known. [unreadable] [unreadable] Our research will address the question of how the structures of putidaredoxin reductase and [unreadable] apoptosis inducing factor are related to their catalytic function. Crystal structures of putidaredoxin reductase and apoptosis inducing factor will be solved, compared, and related to the catalytic properties of the enzymes. From structural interpretations, these relationships will be further probed and modified by genetic engineering and the effect of specific structural changes on catalytic function of the proteins will be assessed. The study will explain the mechanisms of electron transfer and dithiol/disulfide oxidoreduction catalyzed by putidaredoxin reductase and will provide an insight into the mechanism and function of apoptosis inducing factor. [unreadable] [unreadable]