Inhibition of β-amylase activity by calcium, magnesium and zinc ions determined by spectrophotometry and isothermal titration calorimetry

The inhibition effect of metal ions on beta amylase activity was studied. The inhibitor-binding constant (K-i) was determined by spectrophotometric and isothermal titration calorimetric (ITC) methods. The binding of calcium, magnesium and zinc ion as inhibitors at the active site of barley beta amylase was studied at pH=4.8 (sodium acetate 16 mM) and T=300 K. The K-i and enthalpy of binding for calcium (13.4, 13.1 mM and -14.3 kJ/mol), magnesium (18.6, 17.8 mM and -17.7 kJ/mol) and zinc (17.5, 17.7 mM and -20.0 kJ/mol) were found by spectrophotometric and ITC methods respectively.