Document Detail

Sensitized photooxygenation and peroxidase-catalyzed inactivation of xanthine oxidase--evidence of cysteine damage by singlet oxygen.
MedLine Citation:
PMID:  11383136     Owner:  NLM     Status:  MEDLINE    
Xanthine oxidase (XO) has been investigated for its decreased activity in several cancerous tissues and constitutive generation of reactive oxygen species (ROS) in vivo seems to contribute significantly to its inactivation. Singlet oxygen (1O2) production has been suggested to be relevant when considering folic acid metabolism by cancer cells. Thus, the susceptibility of XO to inactivation by 1O2 generated either by the bioenergized systems folic acid/peroxidase/GSH/Mn2+/O2 and malonaldehyde/peroxidase/Mn2+/O2 or by methylene blue (MB) or eosin-sensitized photooxygenation was studied. Our results showed that other ROS were also responsible for XO inactivation when MB was used. In contrast, eosin produced almost exclusively 1O2. Kinetic studies of XO oxidation in the malonaldehyde/peroxidase system showed that histidine (His) is a competitive inhibitor with respect to XO. A similar result was observed in the eosin-photosensitized process, suggesting the involvement of 1O2 in both processes. In addition, an efficient quenching of XO oxidation by guanosine in the folic acid/peroxidase system was observed. Amino acid analysis revealed that cysteine (Cys) is more affected than other XO amino acids also prone to oxidation such as tyrosine (Tyr), methionine (Met) and His. These results indicate that 1O2 may cause oxidative damage to the Cys residues of XO, with loss of enzyme activity. Alteration of the flavin prosthetic site is hypothesized.
G Z Justo; F A Camargo; M Haun; A Faljoni-Alário; N Durán
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Physiological chemistry and physics and medical NMR     Volume:  32     ISSN:  0748-6642     ISO Abbreviation:  Physiol Chem Phys Med NMR     Publication Date:  2000  
Date Detail:
Created Date:  2001-05-31     Completed Date:  2001-10-04     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  8502230     Medline TA:  Physiol Chem Phys Med NMR     Country:  United States    
Other Details:
Languages:  eng     Pagination:  145-54     Citation Subset:  IM    
Instituto de Química, Biological Chemistry Laboratory, Universidade Estadual de Campinas (Unicamp), C.P. 6154, CEP 13083-970, Campinas, S.P., Brazil.
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MeSH Terms
Amino Acids / chemistry
Cysteine / chemistry*
Folic Acid / chemistry
Glutathione / chemistry
Horseradish Peroxidase / chemistry
Indicators and Reagents
Malondialdehyde / chemistry
Peroxidase / chemistry*
Reactive Oxygen Species*
Spectrometry, Fluorescence
Xanthine Oxidase / chemistry*
Reg. No./Substance:
0/Amino Acids; 0/Indicators and Reagents; 0/Reactive Oxygen Species; 52-90-4/Cysteine; 542-78-9/Malondialdehyde; 59-30-3/Folic Acid; 70-18-8/Glutathione; EC 1.11.1.-/Horseradish Peroxidase; EC; EC Oxidase

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