Abortive Complexes of α-Amylases with Lanthanides

Apoamylases from both hog pancreas and Bacillus subtilis were prepared by removing the tightly bound Ca²⁺. In both cases lanthanide ions fail to activate the enzyme. Furthermore, in both cases the rare earth ions do not compete for the essential Ca²⁺ binding site and therefore do not inhibit the Ca²⁺ activation process. B. subtilis α-amylase possesses two Ca²⁺ binding sites, one of which can bind Gd³⁺, with an additional site for the lanthanide ion.