INTERACTION OF DIVALENT METAL-IONS WITH ZN2-GLYCEROPHOSPHOCHOLINE CHOLINEPHOSPHODIESTERASE FROM OX BRAIN()

The effect of divalent metal ions on the activity of glycerophosphocho line cholinephosphodiesterse from ox brain was examined. Zn2+- and Co2 +-glycerophosphocholine cholinephosphodiesterases were prepared from t he exposure of apoenzyme to Zn2+ and Co2+, respectively, and the prope rties of two metallo-phosphodiesterases were compared to those of nati ve phosphodiesterase. Although two metallo-enzymes were similar in exp ressing Km value, optimum pH or sensitivity to Cu2+, they differed in the susceptibility to the inhibition by thiocholine or tellurite; whil e Co2+-phosphodiesterase was more sensitive to tellurites, Zn2+-phosph odiesterase was more susceptible to inhibition by thiocholine. In addi tion, Zn2+-phosphodiesterase was more thermo-stable than Co2+ enzyme. Separately, when properties of native phosphodiesterase were compared to those of each metallo-phosphodiesterase, native phosphodiesterase w as found to be quite similar to Zn2+-phosphodiesterase in many respect s. Even in thermo-stability, native enzyme resembled Zn2+-phosphodiest erase rather than Co2+-enzyme. Consistent with this, the stability of native phosphodiesterase was maintained in the presence of Zn2+, but n ot Co2+. Mn2+ was also as effective as Zn2+ in the stabilization of th e enzyme. Noteworthy, the native enzyme was found to be inhibited comp etitively by Cu2+ With a Ki value of 20 mu M, and its inhibitory actio n was antagonized effectively by Zn2+ or Co2+. Also, choline, another competitive inhibitor of the enzyme, appeared to antagonize the inhibi tory action of Cu2+. Taken together, it is suggested that there may be multiple binding sites for divalent metal ions in the molecule of gly cerophosphocholine cholinephosphodiesterase.