title: Martian Superoxide and Peroxide O2 Release (OR) Assay: A New Technology for Terrestrial and Planetary Applications.
abstract: This study presents an assay for the detection and quantification of soil metal superoxides and peroxides in regolith and soil. The O2 release (OR) assay is based on the enzymatic conversion of the hydrolysis products of metal oxides to O2 and their quantification by an O2 electrode based on the stoichiometry of the involved reactions. The intermediate product O₂˙⁻ from the hydrolysis of metal superoxides is converted by cytochrome c to O2 and by superoxide dismutase (SOD) to ½ mol O2 and ½ mol H2O2, which is then converted by catalase (CAT) to ½ mol O2. The product H2O2 from the hydrolysis of metal peroxides and hydroperoxides is converted to ½ mol O2 by CAT. The assay method was validated in a sealed sample chamber by using a liquid-phase Clark-type O2 electrode with known concentrations of O₂˙⁻ and H2O2, and commercial metal superoxide and peroxide mixed with Mars analog Mojave and Atacama Desert soils. Carbonates and perchlorates, both present on Mars, do not interfere with the assay. The assay lower limit of detection, when using luminescence quenching/optical sensing O2-electrodes, is 1 nmol O2 cm(-3) or better. The activity of the assay enzymes SOD and cytochrome c was unaffected up to 6 Gy exposure by γ radiation, while CAT retained 100% and 40% of its activity at 3 and 6 Gy, respectively, which demonstrates the suitability of these enzymes for planetary missions, for example, on Mars or Europa.
authors.affiliation: 1 Department of Biology, University of Patras , Patras, Greece .
authors.forename: Christos D
authors.initials: CD
authors.lastname: Georgiou
authors.affiliation: 1 Department of Biology, University of Patras , Patras, Greece .
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Zisimopoulos
authors.affiliation: 1 Department of Biology, University of Patras , Patras, Greece .
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Panagiotidis
authors.affiliation: 1 Department of Biology, University of Patras , Patras, Greece .
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Grintzalis
authors.affiliation: 1 Department of Biology, University of Patras , Patras, Greece .
authors.forename: Ioannis
authors.initials: I
authors.lastname: Papapostolou
authors.affiliation: 2 SETI Institute, Carl Sagan Center , Mountain View, California, USA.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Quinn
authors.affiliation: 3 NASA Ames Research Center , Moffett Field, California, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: McKay
authors.affiliation: 4 Desert Research Institute , Las Vegas, Nevada, USA.
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Sun
mesh_terms: D002374:Catalase / Q000378:metabolism; D003198:Computer Simulation; D003576:Electron Transport Complex IV / Q000378:metabolism; D057075:Enzyme Assays / Q000379:methods*; D005720:Gamma Rays; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D018535:Mars; D010100:Oxygen / Q000032:analysis*; D010545:Peroxides / Q000032:analysis*; D012987:Soil; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000032:analysis*
chemical_list: D010545:Peroxides; D012987:Soil; D013481:Superoxides; D002374:Catalase; D013482:Superoxide Dismutase; D003576:Electron Transport Complex IV; D010100:Oxygen