Abstract/Details

A tale of sulfur and selenium metabolites: From dioxygenases with sulfur-containing substrates to the analysis of selenium by gas chromatography with atomic emission detection


2006 2006

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Abstract (summary)

Sulfur and selenium participate in a variety of essential biological functions. The investigation of two non-heme iron dioxygenases with sulfur-containing substrates is reported along with studies of seleno-compounds by gas chromatography with atomic emission detection (GC-AED).

Cysteine dioxygenase (CDO) catalyzes the oxidation of cysteine to cysteine sulfinic acid, which is the first major step in cysteine catabolism in mammalian tissues. Rat liver CDO was cloned and expressed in E. coli as a 26.8 kDa fusion protein bearing a poly-histidine tag. Kinetics studies revealed a Km value of 2.5 ± 0.4 mM at pH 7.5 and 37 °C, with no requirement for secondary proteins or cofactors. Fe was demonstrated to be the only metal that is essential for activity. Inhibition studies with cysteine analogs along with the use of x-ray absorption spectroscopy (XAS) allowed for the characterization of the active site.

Acireductone dioxygenases (ARDs) are enzymes involved in the methionine recycle pathway. Klebsiella produces two ARD enzymes that share a common polypeptide sequence and differ only in the metal ion present. In the presence of Fe-containing ARD (ARD'), reaction of acireductone with dioxygen produces formate and the ketoacid precursor of methionine. In the presence of the Ni-bound form (ARD) the same substrate produces formate, methylthiopropionate and CO, an off-pathway shunt. XAS study of the structure of the catalytic Fe center in resting state enzyme shows a six coordinate Fe site composed of N/O-donor ligands including 3-4 histidine residues. The substrate binds to the Fe center in a bidentate fashion by displacing two ligands, at least one of which is a histidine ligand.

Cancer prevention attributed to the properties of selenium is widely recognized, but the mechanism of tumor inhibition by this element is still not known. The determination of Se-metabolites and the understanding of their fate are indispensable. Liver extracts from rats administered with selenized yeast were examined by GC-AED. Organoseleno compounds have been observed, including selenomethionine, and possibly the newly-discovered S-(methylseleno)-cysteine molecule. Aromatic Se-compounds have been recognized as antitumorigenic alternatives with lower toxicity. Gas chromatographic behavior of several aryl diselenide derivatives were analyzed.

Indexing (details)


Subject
Chemistry;
Analytical chemistry
Classification
0488: Chemistry
0486: Analytical chemistry
Identifier / keyword
Pure sciences, Atomic emission detection, Dioxygenases, Gas chromatography, Metabolites, Selenium, Sulfur
Title
A tale of sulfur and selenium metabolites: From dioxygenases with sulfur-containing substrates to the analysis of selenium by gas chromatography with atomic emission detection
Author
Chai, Sergio C.
Number of pages
211
Publication year
2006
Degree date
2006
School code
0118
Source
DAI-B 67/11, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780542977527
Advisor
Maroney, Michael J.; Uden, Peter C.
University/institution
University of Massachusetts Amherst
University location
United States -- Massachusetts
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3242320
ProQuest document ID
305306093
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/305306093
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