Enhanced thermal stability and pH behavior of glucose oxidase on electrostatic interaction with polyethylenimine

Electrostatic interactions, mediated by ionic-exchange, between polyethylenimine (PEI) and glucose oxidase (GOx) were used to form GOx-PEI macro-complex, which were evaluated for pH and thermal stability of GOx. Under the experimental conditions, the complex had a dominant GOx presence on its surface and a hydrodynamic diameter of 205 +/- 16 nm. Activity was evaluated from 40 to 75 degrees C, and at pH from 2 to 12. GOx activity in complex was maintained up to 70 degrees C and it was lost at 75 degrees C. In contrast, free GOx showed a maximum activity at 50 degrees C, which was completely lost at 70 degrees C. This difference, observed by fluorescence analysis, was associated with the compact unfolded structure of GOx in the complex. This GOx stability was not observed under pH variations, and complex formation was only possible at pH >= 5 where enzymatic activity was diminished by the presence of PEI. (C) 2015 Elsevier B.V. All rights reserved.