Metal Ion Relevance for the Stability and Activity of a 52-kDa Serratia Proteinase

A 52-kDa metalloproteinase from Serratia marcescens (Serratia marcescens extracellular proteinase, EC 3.4.24.4) was purified to homogeneity and studied for the roles of metal ions. There were 1 zinc and 7 calcium atoms per molecule of the enzyme. Although the enzyme activity was almost eliminated by treatments with EDTA and tetraethylenepentamine up to 10 mM at room temperature, the fluorescence emission properties of the enzyme were not affected appreciably by the same treatments. The guanidine hydrochloridemediated unfolding of the enzyme molecules, which was accompanied by changes in fluorescence emission properties and elimination of enzyme activity, was considerably accelerated by the presence of 4 mM EDTA. The thermal unfolding profiles varied according to the microenvironment of the enzyme molecules. The selective substitution ofcalcium for functional zinc atom did not change the stability of the enzyme appreciably below 55°C. The activity of the EDTA-inactivated enzyme was largely restored by the additions of Zn(2+), Ca(2+), Mn(2+), Mg(2+), and Fe(2+) ions.