There is a significant inter-individual variability in susceptibility to progression from arsenic exposure to clinical manifestations of arsenic toxicity (e.g. skin, lung, liver and bladder cancers). A major project in this lab is to determine the impact of nutritional status on As metabolism and toxicity. Methylation of inorganic arsenic (InAs) is generally considered to be a detoxification pathway. InAs and DNA are both methylated via one-carbon metabolism, a biochemical pathway that is dependent on folate for de novo generation of one-carbon groups, and also uses vitamins B12 and B6 as cofactors. We have therefore set out to determine if nutritional regulation of one-carbon metabolism, specifically folate availability, contributes substantially to the large inter-individual variability observed in InAs and DNA methylation, and thus progression from arsenic exposure to toxicity. Methylation of InAs also requires that the pentavalent arsenic species first be reduced to trivalent species in a glutathione-dependent process. Regeneration of oxidized glutathione is accomplished by glutathione reductase, an enzyme that is strongly inhibited by arsenic. Another study in the lab explores the relationship between arsenic exposure, antioxidant status, and oxidative DNA damage. In Idiopathic Parkinson's disease (IPD), iron homeostasis is abnormal and the activity of Complex 1 of the mitochondrial respiratory chain is diminished. We therefore conducted studies to better understand the regulation of the Fe-S subunits of Complex 1. These studies ultimately led to the discovery of a new iron regulatory protein (IRP3), which binds to a novel stem-loop structure in the 5' untranslated region of the mRNA encoding the 75 kDa 4Fe-4S subunit of Complex 1. A primary hypothesis of this work is that the 75 kDa Fe-S-containing subunit of Complex 1 is regulated by a novel IRE-IRP system. The purification, identification, and characterization of IRP3 are the primary goals of this project.