Effect of Mg2+ and Al3+ Ions on Thermodynamic and Physiochemical Properties of Aspergillus niger Invertases

In the present study, we reported for the first time the effect of various concentrations (0.5– 3.0 mM) of Mg2+ and Al3+ ions on the kinetics and thermodynamics of Aspergillus niger invertases for sucrose hydrolysis. We found that both metal ions enhanced the affinity of invertase for sucrose by decreasing the Km. In the presence of 0.5 mM Al3+ ions invertase have maximum affinity for sucrose (Km = 0.00914 M sucrose). Invertase was activated by Mg2+ ions at low concentrations (0.5–2.0 mM) and 341% increase in turnover (Kcat) and maximum decrease in ΔG* was observed in the presence of 0.5 mM Mg2+ ions. The entropy change for activation of substrate hydrolysis (ΔS*) was increased by all concentrations of Mg2+ ions and was highest (-94 J mol-1 K-1) for invertases bound with 1.5 mM Mg2+ ions.