title: Monovalent cation-induced conformational change in glucose oxidase leading to stabilization of the enzyme.
abstract: Glucose oxidase (GOD) from Aspergillus niger is an acidic dimeric enzyme having a high degree of localization of negative charges on the enzyme surface and dimer interface. We have studied the effect of monovalent cations on the structure and stability of GOD using various optical spectroscopic techniques, limited proteolysis, size exclusion chromatography, differential scanning calorimetry, and enzymic activity measurements. The monovalent cations were found to influence the enzymic activity and tertiary structure of GOD, but no effect on the secondary structure of the enzyme was observed. The monovalent cation-stabilized GOD was found to have a more compact dimeric structure but lower enzymic activity than the native enzyme. The enzyme's K(m) for D-glucose was found to be slightly enhanced for the monovalent cation-stabilized enzyme (maximum enhancement of about 35% for LiCl) as compared to native GOD. Comparative denaturation studies on the native and monovalent cation-stabilized enzyme demonstrated a significant resistance of cation-stabilized GOD to urea (about 50% residual activity at 6.5 M urea) and thermal denaturation (Delta T(m) maximum of 10 degrees C compared to native enzyme). However, pH-induced denaturation showed a destabilization of monovalent cation-stabilized GOD as compared to the native enzyme. The effectiveness of monovalent cations in stabilizing GOD structure against urea and thermal denaturation was found to follow the Hofmeister series: K(+) > Na(+) > Li(+).
authors.affiliation: Division of Membrane Biology, Central Drug Research Institute, Lucknow 226 001, India.
authors.forename: A
authors.initials: A
authors.lastname: Ahmad
authors.forename: M S
authors.initials: MS
authors.lastname: Akhtar
authors.forename: V
authors.initials: V
authors.lastname: Bhakuni
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology; D001665:Binding Sites; D001974:Bromosuccinimide / Q000378:metabolism; D002152:Calorimetry, Differential Scanning; D002414:Cations, Monovalent / Q000737:chemistry*; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003432:Cross-Linking Reagents / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation; D004795:Enzyme Stability; D005947:Glucose / Q000378:metabolism; D005949:Glucose Oxidase / Q000737:chemistry* / Q000378:metabolism*; D005976:Glutaral / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D018021:Lithium Chloride / Q000737:chemistry; D011189:Potassium Chloride / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D012965:Sodium Chloride / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D014364:Tryptophan / Q000378:metabolism; D014508:Urea
chemical_list: D002414:Cations, Monovalent; D003432:Cross-Linking Reagents; D012965:Sodium Chloride; D011189:Potassium Chloride; D014364:Tryptophan; D014508:Urea; D005949:Glucose Oxidase; D010450:Endopeptidases; D018021:Lithium Chloride; D005947:Glucose; D001974:Bromosuccinimide; D005976:Glutaral