Document Detail

Cell bound and extracellular glucose oxidases from Aspergillus niger BTL: evidence for a secondary glycosylation mechanism.
MedLine Citation:
PMID:  18025566     Owner:  NLM     Status:  MEDLINE    
Two glucose oxidase (GOX) isoforms where purified to electrophoretic homogeneity from the mycelium extract (GOXI) and the extracellular medium (GOXII) of Aspergillus niger BTL cultures. Both enzymes were found to be homodimers with nonreduced molecular masses of 148 and 159 kDa and pI values of 3.7 and 3.6 for GOXI and GOXII, respectively. The substrate specificity and the kinetic characteristics of the two GOX forms, as expressed through their apparent K m values on glucose, as well as pH and T activity optima, were almost identical. The only structural difference between the two enzymes was in their degrees of glycosylation, which were determined equal to 14.1 and 20.8% (w/w) of their molecular masses for GOXI and GOXII, respectively. The above difference in the carbohydrate content between the two enzymes seems to influence their pH and thermal stabilities. GOXII proved to be more stable than GOXI at pH values 2.5, 3.0, 8.0, and 9.0. Half-lives of GOXI at pH 3.0 and 8.0 were 8.9 and 17.5 h, respectively, whereas the corresponding values for GOXII were 13.5 and 28.1 h. As far as the thermal stability is concerned, GOXII was also more thermostable than GOXI as judged by the deactivation constants determined at various temperatures. More specifically, the half-lives of GOXI and GOXII, at 45 degrees C, were 12 and 49 h, respectively. These results suggest A. niger BTL probably possesses a secondary glycosylation mechanism that increases the stability of the excreted GOX.
Dimitris G Hatzinikolaou; Diomi Mamma; Paul Christakopoulos; Dimitris Kekos
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Applied biochemistry and biotechnology     Volume:  142     ISSN:  0273-2289     ISO Abbreviation:  Appl. Biochem. Biotechnol.     Publication Date:  2007 Jul 
Date Detail:
Created Date:  2007-11-20     Completed Date:  2008-01-02     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8208561     Medline TA:  Appl Biochem Biotechnol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  29-43     Citation Subset:  IM    
Laboratory of Microbiology, Department of Botany, School of Biology, National and Kapodistrian University of Athens, Panepistimioupoli Zografou, Athens, Greece.
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MeSH Terms
Aspergillus niger / enzymology*
Biotechnology / methods*
Carbohydrates / chemistry
Glucose / chemistry
Glucose Oxidase / chemistry*,  metabolism
Hydrogen-Ion Concentration
Isoelectric Point
Molecular Weight
Mycelium / chemistry
Protein Isoforms
Substrate Specificity
Reg. No./Substance:
0/Carbohydrates; 0/Protein Isoforms; 50-99-7/Glucose; EC Oxidase

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