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Your search keyword '"Sima, A. D."' showing total 14 results
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14 results on '"Sima, A. D."'

4. Inactivation of Glucose Oxidase by Diperoxovanadate-Derived Oxidants

Author

Rao, Aparna VS, Sima, Paul D, Kanofsky, Jeffrey R, and Ramasarma, T

Subjects
Biochemistry
Abstract

Inactivation of glucose oxidase occurred in the presence of bromide, vanadate, $H_2O_2$, and phosphate (the bromide system), and this was prevented by NADH or phenol red, a bromine acceptor. Glucose oxidase present during the reaction between diperoxovanadate and a reduced form of vanadate, vanadyl (the vanadyl system), but not added after mixing the reactants, was inactivated, and this was accompanied by a loss of binding of the dye, Coomassie blue, to the protein. The transient intermediate of the type $OVOOV(O_2)$, known to form in these reactions and used in the oxidation of bromide ion and NADH, appears to be responsible for inactivating glucose oxidase. In both systems, the inactivation of the enzyme was prevented by histidine and DTT, known to quench singlet-oxygen. By direct measurement of 1270-nm emission of singlet-oxygen, its generation was demonstrated in the bromide system, and in the reaction of hypohalous acids with diperoxovanadate, but not in the vanadyl system. By themselves both hypohalous acids, HOCl and HOBr inactivated glucose oxidase, and their prior reaction with $H_2O_2$ during which singlet-oxygen was released, protected the enzyme. The results provide support for possible oxidative inactivation of glucose oxidase by diperoxovanadate-derived oxidants.

Published
1999

6. Quenching of Singlet Oxygen by a Carotenoid–Cyclodextrin Complex: The Importance of Aggregate Formation.

Author

Kanofsky, Jeffrey R. and Sima, Paul D.

Subjects
*OXYGEN, *CAROTENOIDS, *CYCLODEXTRINS, *SOLUBILITY, *AMMONIUM compounds, *ORGANOBROMINE compounds
Abstract

The Girard’s reagent P derivative of canthaxanthin ((GRP)2-canthaxanthin), a dicationic carotenoid, forms a highly water-dispersible complex with (2-hydroxypropyl)-γ-cyclodextrin. The UV–visible light spectrum of the complex is consistent with some degree of aggregation, but the spectrum is independent of concentration from 7.5 to 750 μm. Stern-Vomer plots for singlet-oxygen quenching by the complex are linear over a concentration range of 0–20 μm. In the presence of 1 mm (2-hydroxypropyl)-γ-cyclodextrin, the singlet-oxygen quenching constant for the complex is 7.9 ± 0.9 × 108 m−1s−1. This is about an order of magnitude lower than the singlet-oxygen quenching constants for (GRP)2-canthaxanthin in various organic solvents. The properties of the complex are also compared with the properties of (GRP)2-canthaxanthin solubilized in neat water and in water containing various detergents. The singlet-oxygen quenching constant for (GRP)2-canthaxanthin in micelles depends strongly on the specific detergent used, varying from 9.4 × 108 m−1s−1 for hexadecyltrimethylammonium bromide (CTAB) to 1.24 ± 0.4 × 1010 m−1s−1 for sodium dodecyl sulfate. The small quenching constant in CTAB micelles correlates with spectroscopic evidence for aggregation of the (GRP)2-canthaxanthin in this detergent. [ABSTRACT FROM AUTHOR]

Published
2009
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