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6. Light emission accompanies oxygen uptake during the peroxidative metabolism of tetracyclines

Author

Gilio Ve and Cilento G

Subjects
Light, Tetracycline, chemistry.chemical_element, Photochemistry, Biochemistry, Horseradish peroxidase, Oxygen, law.invention, chemistry.chemical_compound, law, medicine, Physical and Theoretical Chemistry, Hydrogen peroxide, Horseradish Peroxidase, Chemiluminescence, biology, Spectrum Analysis, General Medicine, Metabolism, Hydrogen Peroxide, chemistry, biology.protein, Light emission, medicine.drug, Peroxidase, Chlortetracycline
Abstract

Tetracycline molecules offer several sites for peroxidative metabolism of the type known to lead to oxygen consumption and electronic excitation. Accordingly, when tetracycline and chlortetracycline were exposed to horseradish peroxidase in the presence of hydrogen peroxide, oxygen was taken up and light emission was observed. The overall quantum yield of chemiluminescence is on the order of 10(-6), but that of chemiexcitation may be orders of magnitude higher as suggested by studies of sensitized emission. Given the widespread distribution of peroxidases, the formation of highly reactive metabolites of tetracycline may have biological importance.

Published
1993

17. Peroxidase-catalyzed formation of triplet acetone and chemiluminescence from isobutyraldehyde and molecular oxygen.

Author

Baader, W J, Bohne, C, Cilento, G, and Dunford, H B

Abstract

It has been established that the horseradish peroxidase/O2/isobutyraldehyde (IBAL) system leads to triplet acetone and formic acid formation followed by phosphorescence of the triplet acetone (see, for example, Bechara, E.J.H., Faria Oliveira, O.M.M., Durán, N., Casadei de Baptista, R., and Cilento, G. (1979) Photochem. Photobiol. 30, 101-110). In this paper many of the mechanistic details are established. The reaction is initiated by the autoxidation of IBAL to form the peracid (CH3)2CHC = O(OOH). The peracid converts horseradish peroxidase into compound I which in turn is converted into compound II by abstracting the alcoholic hydrogen atom from the enol form of IBAL. This creates a free radical with two resonance forms. (Formula: see text) Addition of molecular oxygen to the latter resonance form creates a peroxy radical which abstracts a hydrogen atom near the active site of the enzyme. The newly formed alpha-peroxide in turn forms a dioxetane-type of intermediate which rapidly decomposes into triplet acetone and formic acid. Compound II reacts with the enol by the same pathway as compound I. Thus native horseradish peroxidase is regenerated. The hydrogen atom abstraction near the enzyme active site may occur directly from ethanol, present to solubilize IBAL or from a group on the enzyme, in which case ethanol participates in a repair mechanism. Phosphate buffer is necessary because it catalyzes the keto-enol conversion of IBAL. Thus horseradish peroxidase participates in a normal peroxidatic cycle. The only chain reaction is the uncatalyzed autoxidation of IBAL, most of which occurs prior to the mixing of IBAL with the oxygenated horseradish peroxidase solution.

Published
1985
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