Freeze-thawing induced structural and functional changes in glucose oxidase.

BACKGROUND: Glucose oxidase enzyme may be a suitable model for studying the effect of low temperatures on structural and functional properties of biomacromolecules. OBJECTIVE: The research aim was to study the freeze-thawing effect on glucose oxidase isolated and immobilized by cross-linking with glutaraldehyde METHODS: Effects of freezing rates on conformation and activity of glucose oxidase isolated and cross-linked in solution with gluteraldehyde was studied. RESULTS: Freezing with slow rate (2 degree C per min) induces significant protein aggregation, activity reduction and conformational changes in polar and hydrophobic regions. Freezing at 100 degree C per min, however, causes conformational changes primarily in polar regions, insignificant aggregation, depending on the number of freeze-thawing cycles and increases enzyme activity. CONCLUSION: With the rise in glucose oxidase concentration in solution the low temperature-induced destabilization effect is reduced both during low and rapid freezing. At the slow cooling rate, cross-linking with glutaraldehyde results in more conformation alterations in polar regions of proteins, accompanied with an increase in enzyme activity.