title: The catalase activity of diiron adenine deaminase.
abstract: Adenine deaminase (ADE) from the amidohydrolase superfamily (AHS) of enzymes catalyzes the conversion of adenine to hypoxanthine and ammonia. Enzyme isolated from Escherichia coli was largely inactive toward the deamination of adenine. Molecular weight determinations by mass spectrometry provided evidence that multiple histidine and methionine residues were oxygenated. When iron was sequestered with a metal chelator and the growth medium supplemented with Mn(2+) before induction, the post-translational modifications disappeared. Enzyme expressed and purified under these conditions was substantially more active for adenine deamination. Apo-enzyme was prepared and reconstituted with two equivalents of FeSO(4). Inductively coupled plasma mass spectrometry and Mössbauer spectroscopy demonstrated that this protein contained two high-spin ferrous ions per monomer of ADE. In addition to the adenine deaminase activity, [Fe(II) /Fe(II) ]-ADE catalyzed the conversion of H(2)O(2) to O(2) and H(2)O. The values of k(cat) and k(cat)/K(m) for the catalase activity are 200 s(-1) and 2.4 × 10(4) M(-1) s(-1), respectively. [Fe(II)/Fe(II)]-ADE underwent more than 100 turnovers with H(2)O(2) before the enzyme was inactivated due to oxygenation of histidine residues critical for metal binding. The iron in the inactive enzyme was high-spin ferric with g(ave) = 4.3 EPR signal and no evidence of anti-ferromagnetic spin-coupling. A model is proposed for the disproportionation of H(2)O(2) by [Fe(II)/Fe(II)]-ADE that involves the cycling of the binuclear metal center between the di-ferric and di-ferrous oxidation states. Oxygenation of active site residues occurs via release of hydroxyl radicals. These findings represent the first report of redox reaction catalysis by any member of the AHS.
authors: Department of Chemistry, Texas A&M University, College Station, Texas 77843-3012, USA.
authors: Siddhesh S
authors: SS
authors: Kamat
authors: Gregory P
authors: GP
authors: Holmes-Hampton
authors: Ashima
authors: A
authors: Bagaria
authors: Desigan
authors: D
authors: Kumaran
authors: Shane E
authors: SE
authors: Tichy
authors: Tarun
authors: T
authors: Gheyi
authors: Xiaojing
authors: X
authors: Zheng
authors: Kevin
authors: K
authors: Bain
authors: Chris
authors: C
authors: Groshong
authors: Spencer
authors: S
authors: Emtage
authors: J Michael
authors: JM
authors: Sauder
authors: Stephen K
authors: SK
authors: Burley
authors: Subramanyam
authors: S
authors: Swaminathan
authors: Paul A
authors: PA
authors: Lindahl
authors: Frank M
authors: FM
authors: Raushel
mesh_terms: D000619:Aminohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D006861:Hydrogen Peroxide / Q000378:metabolism; D017665:Hydroxyl Radical / Q000378:metabolism; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D016296:Mutagenesis; D010084:Oxidation-Reduction; D013481:Superoxides / Q000378:metabolism
chemical_list: D013481:Superoxides; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D007501:Iron; D002374:Catalase; D000619:Aminohydrolases; C018774:adenine deaminase