Effect of Ca+2 and K+ ions on Thermal Stability of Geobacillus Maltogenic Amylase

Maltogenic Amylases (MAase) are a subfamily of Į-amylase family that can hydrolyze multiple substrates including starch، pullulan and cyclodextrins however، they prefer cyclodextrins to others، and unlike other Į-amylases، they are intracellular. This enzyme has the potential for use in many industrial processes such as food، fermentation and pharmacy. The effect of different concentrations of Ca2+ and K+ ions on irreversible thermoinactivation of the enzyme at 65 ÛC showed that Ca2+ and K+ decreased and increased its thermal stability. The CD spectra of the enzyme in the presence and absence of metal ions were measured to detect changes in the secondary structure contents. The spectra showed a decrease in the Į-helix content in the presence of 1 and 10 mM of Ca2+، but in the presence of 5 mM، a drastic increase in Į-helix content of the enzyme was witnessed. In the presence of 1 and 5 mM of Na+ the Į-helix content decreased، while it was increased in the presence of 10 mM. The results from intrinsic fluorescence of the protein (excitation at 280 nm) indicated that Ca2+ ion at 1 and 5 mM caused an increase in tertiary structure of the enzyme; however، at 10 mM، a decrease was observed in its tertiary structure. K+ ion at all concentrations increased the tertiary structure of the enzyme. These spectroscopic results are in a good agreement with the thermostability data. It was shown that destabilizing effect of calcium was enthalpic (decrease in ǻH#) whereas the stabilizing effect of potassium was entropic (decrease in ǻS#).