Production, Purification and Thermodynamic Characterization of a New α-Glucosidase from the Cyanobacterium Pseudanabaena sp.

An intracellular α-glucosidase was isolated and purified from a Pseudanabaena sp. cyanobacterial strain. Before the enzyme purification, the optimal cultural conditions were determined. Optimal culture conditions (15 g/L maltose, 2 g/L yeast extract, 23 ± 1 °C) yielded 3.3 g/L of biomass and 2186 U/L of α-glucosidase in a lab-scale bioreactor. The purified enzyme displayed a molecular mass of 52 kDa with optimum activity at 40 °C and pH 7.0, and maintained stability within an acidic and neutral range of pH 4.0 to 7.0. Enzyme activity was affected by both the concentration and interaction time of the metal ions and chelator. Kinetic constants of Km, Vmax, and kcat for the hydrolysis of pNPG were determined as 2.0 Mm, 2.9 μmol min−1, and 14.86 min−1, respectively. The activation energy (Ea) was 24.2 kJ mol−1 and the thermodynamic parameters of enthalpy (ΔH*), entropy (ΔS*) of activation, Gibbs free energy (ΔG*), free energy of substrate binding (ΔG*E-S), and transition state formation (ΔG*Ε-Τ) were 21.6, −116, 57.8, −22.2, and −41.2 kJ mol−1, respectively. Moreover, the thermodynamic parameters for thermal inactivation of the enzyme were ΔH*= 131 kJ mol−1, 105 ≤ ΔS* ≤ 108 kJ mol−1, and 96 ≤ ΔG* ≤ 98 kJ mol−1, while the thermal inactivation energy (E(a)d) was determined to be 133 kJ mol−1. This is the first detailed investigation concerning the characterization of α-glucosidase derived from cyanobacteria. The presented enzymatic characteristics provide a valuable predictive model for identifying suitable applications.