[Influence of Zn++ and of Mg++ on alkaline phosphatase activity of different origins]

Many researches have shown the role of some bivalent ions on the structure and function of alkaline phosphatase. For this reason we considered interesting to assay the effect of Zn++ and Mg++, at various concentrations, on the activity of alkaline phosphatase (APase) from different sources. The isoenzymes of alkaline phosphatase used for the experiments were from rat kidney and bone, from calf intestinal mucosa and from Escherichia coli. In order to investigate the effect of Zn++ and Mg++ on the enzyme activity, the two ions were removed using EDTA as chelating agent. The residual enzymatic activity was measured after having preincubated for 15 min the enzyme with EDTA at a final concentration of 0.05 mM, 0.1 mM, 0.5 mM, 5 mM, 25 mM. The reactivation of the enzyme was studied using as reference a sample, in which the final concentration of EDTA was 5 mM. In these series of experiments the enzymatic activity was assayed after a preincubation of the reaction mixture with ZnCl2 10 mM, MgCl2 10 mM and ZnCl2 +MgCl2 10 mM. The inactivation in the time of the enzyme by 5 mM EDTA was also studied. The results obtained show that APase from intestinal mucosa maintained, at the lower concentrations of EDTA (0.05, 0.1 and 0.5 mM), a residual activity higher than that of the enzymes of other source. Moreover, whilst the activity of the mucosal enzyme was completely restored by the addition of Zn++, the complete reactivation of the other enzyme activities was obtained only by the addition of Zn++ and Mg++ together. Concerning the inactivation by EDTA during the time, it was shown that APase from calf intestinal mucosa was inactivated after 60 min of incubation, while the enzymes from other sources lost completely their activity after 10 min.