Doctor of Philosophy (PhD)
First Advisor's Name
Prof. Barry P Rosen
First Advisor's Committee Title
Second Advisor's Name
Dr. Masafumi Yoshinaga
Second Advisor's Committee Title
Third Advisor's Name
Dr. Jeremy Chambers
Third Advisor's Committee Title
Fourth Advisor's Name
Prof. Yong Cai
Fourth Advisor's Committee Title
Fifth Advisor's Name
Dr. Konstantinos Kavallieratos
Fifth Advisor's Committee Title
ArsI, C-As lyase, roxarsone, MSMA, organoarsenical herbicides, organoarsenical growth promoters, type I extradiol dioxygenases, arsenite, mass spectrometry, HPLC
Date of Defense
Organoarsenicals such as methylarsenical methylarsenate (MAs(V)) and aromatic arsenicals including roxarsone (4-hydroxy-3-nitrophenylarsenate or Rox(V)) have been extensively used as an herbicide and growth enhancers in animal husbandry, respectively. They undergo environmental degradation to more toxic inorganic arsenite (As(III)) that contaminates crops and drinking water. We previously identified a bacterial gene (arsI) responsible for aerobic MAs(III) demethylation. The gene product, ArsI, is a Fe(II)-dependent extradiol dioxygenase that cleaves the carbon-arsenic (C-As) bond in MAs(III) and trivalent aromatic arsenicals. The objective of this study was to elucidate the ArsI mechanism. Using isothermal titration calorimetry, we determined the dissociation constants (Kd) and ligand-to-protein stoichiometries (N) of ArsI for Fe(II), MAs(III) and aromatic phenyl arsenite. Using a combination of methods including chemical modification, site-directed mutagenesis, and fluorescent spectroscopy, we demonstrated that amino acid residues predicted to participate in Fe(II)-binding (His5-His62-Glu115) and substrate binding (Cys96-Cys97) are all involved in catalysis. Finally, the products of Rox(III) degradation were identified as As(III) and 4-hydroxy-2-nitrophenol, demonstrating that ArsI is a dioxygenase that incorporates one oxygen atom from dioxygen into the carbon and the other to the arsenic to catalyze the cleavage of the C-As bond. These results augment our understanding of the mechanism of this novel C-As lyase.
Pawitwar, Shashank Suryakant, "Biochemical characterization of ArsI: a novel C-As lyase for degradation of environmental organoarsenicals" (2017). FIU Electronic Theses and Dissertations. 3470.
Available for download on Friday, July 13, 2018
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