Abstract
The thermal unfolding of Rhizopus glucoamylase (EC 3.2.1.3) was studied at pH7 by high-sensitivity differential scanning calorimetry (DSC). The DSC curve showed a single irreversible asymmetric peak having the temperature of maximal excess specific heat, tp, at around 57°C. The curve was resolved into two components according to the model of independent two-state processes. In the presence of SGI (5-amino-1, 5-dideoxy D-glucopyranose), a sugar inhibitor of the enzyme, tp increased with increasing concentration of SGI. Analysis of the DSC data of the enzyme-SGI complex suggests two independent domains with dissociation of SGI in the second component.
