Zircon (ZrSiO4) is a common accessory mineral in nature, occurring in a wide variety of sedimentary, igneous, and metamorphic rocks. Known to incorporate an assortment of minor and trace elements, zircon has the ability to retain substantial chemical and isotopic information, leading to its use in a wide range of geochemical investigations, including studies on the evolution of Earth’s crust and mantle (e.g., Hanchar et al. 1994, Bowring 1995, Vervoort et al. 1996, Hoskin and Schaltegger, this volume; Valley, this volume) as well as age dating (e.g., Gibson and Ireland 1995, Bowring et al. 1998, Solar et al. 1998, Bowring and Schmitz, this volume; Ireland and Williams, this volume; Parrish et al., this volume). The physical and chemical durability of zircon is a major factor in it being the mineral by which many of Earth’s oldest known rocks have been dated (Bowring et al. 1989, Maas et al. 1992, Buick et al. 1995, Bowring and Williams 1999, Wilde et al. 2001) and is also an important factor in zircon being proposed as a candidate waste form for the geologic disposal of excess plutonium from dismantled nuclear weapons (Ewing and Lutze 1997, Ewing 1999, Burakov et al. 2002, Burakov et al. 2003, Ewing et al., this volume).

The chemical and physical properties of zircon and its ability to incorporate and retain trace elements are largely determined by its crystal structure. The zircon structure is adopted by numerous minerals and synthetic compounds with the general formula AT O4, in which high field-strength T -site cations occupy isolated tetrahedra, and A -site cations occupy larger eight-coordinated structural sites. Zircon-type compounds share many physical properties, as well as displaying variable degrees of solid solution among end members. …

Structure and Chemistry of Zircon and Zircon-Group Minerals

S p e c ifi c ialty nctio f.-th e E n z y m e .__ '''.'''.'.........-.''.--''''''''''''''''-'-' -'-''''113 Specifici y of the Enzyme 134 Chemistry of the Enzyme ..... 135 Mechanism of Action 13 5 Oxidation Products.13 8 Factors Influencing Action.141 Temperature, Oxygen, Time, Concentrations .141 1H.141 Natural Inhibitors.141 Occurrence and Distribution.143 Chemistry.143 Physiological Function.144 Lght.144 Daylength.146 Chemical Promoters.147 Coenzymes ... 147 Inhibitor Removers and Inactivators.150 Chemical Inhibitors 151 Direct Enzyme Inhibitors . .. .151 Com petitive Inhibitors 1.........5.. 141 Coenzyme Oxidation ......... 153 Natural Inhibitor Promotion. 153 Non-enzymatic Destruction of IAA 156 Assay Techniques 157 Extraction and Puriication 157 Incubation .Rv . ..... 157 Determination ......... 158 Literature Citedn.158.xiato 158

Indoleacetic acid oxidase

Extracts from roots of Nicotiana tabacum L var. Bottom Special contain oxidative enzymes capable of rapid degradation of indoleacetic acid (IAA) in the presence of Mn2+ and 2, 4-dichlorophenol. Purification of IAA oxidase was attempted by means of ammonium sulfate fractionation and elution through a column of SE-Sephadex. Two distinct fractions, both causing rapid oxidation of IAA in the absence of H2O2, were obtained. One fraction exhibited high peroxidase activity when guaiacol was used as the electron donor; the other did not oxidase guaiacol. Both enzyme fractions caused similar changes in the UV spectrum of IAA; absorption at 280 mμ was reduced, while major absorption peaks appeared at 254 and 247 mμ. The kinetics of IAA oxidation by both fractions were followed by measuring the increase in absorption at 247 mμ. The peroxidase-containing fraction showed no lag or a slight lag which could be eliminated by addition of H2O2 (3 μmoles/ml). The peroxidase-free fraction showed a longer lag, but addition of similar amounts of H2O2 inhibited the rate of IAA oxidation and did not remove the lag. With purified preparations, IAA oxidation was stimulated only at low concentrations of H2O2 (0.03 μmole/ml). A comparison of Km values for IAA oxidation by the peroxidase-containing and peroxidase-free fractions suggests that tobacco roots contain an IAA oxidase which may have higher affinity for IAA and may be more specific than the general peroxidase system previously described from other plant sources. A similar oxidase is present in commercial preparations of horseradish peroxidase. It is suggested that oxidation of IAA by horseradish peroxidase may be due to a more specific component.

Partial Purification and Kinetics of Indoleacetic Acid Oxidase from Tobacco Roots

The Effects of Flavonoid Compounds on Oxidative Phosphorylation and on the Enzymatic Destruction of Indoleacetic Acid

The Indole-3-Acetic Acid Oxidase of Lupinus albus L.

Interference in Salkowski assay of indoleacetic acid.

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Interference in Salkowski assay of indoleacetic acid.