The effect of calcium on the activation of thermolysin by salt

Thermolysin, obtained from bacillus thermoproteolyticus, is a thermophilic protease having application in peptide synthesis. Previous studies have revealed that salt activates the enzyme. Thermal stability of TLN is critically dependent on four calcium ions bound in N- and C-terminal domains. The aim of present study is unraveling the role of calcium ions in the salt activation of enzyme. On the presence of NaCl 2 M, measurement of the activity of enzyme in the absence and presence of CaCl2 10 mM using FAGLA as substrate showed activation of enzyme using FAGLA and in the presence of CaCl2 10 mM increased 2.5 times. Circular dichroism and fluorescence spectroscopies were used to understand the calcium dependent changes in the enzyme structure. Circular dichroism spectra suggest that the overall structure of thermolysin has not changed during salt and calcium activation. However, fluorescence studies revealed that the active site has changed under calcium-dependent salt activation. According to the results of the present study, the binding of calcium ions might influence the activation of thermolysin by salt.