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In summarizing the results obtained from the experiment on ??-ALAD activity by adding 6 kinds of heavy metals and EDTA, a chelating agent, at different concentrations ranging from 1.5×10^-7 M to 1×10^-2 M in vitro to hepatic ??-ALAD partially purified from ICR strain of mice, the following conclusions can be drawn. Zn^++, a constitutive element of the enzyme, behaves as an activator at low concentration below 6×10^-5 M, and as an inhibitor at higher concentration above 1.5×10^4 M. The same effect is noted with Al^+++ and Hg^++, although inhibitory action of these two metals appears at higher concentration than Zn^++. Both Pb^++ and Cu^++ are the potent inhibitor of the enzyme, and the Cu^++’ acts as more potent inhibitor than Pb^++, EDTA, a chelating agent, also acts as a powerful inhibitor of the enzyme. It can be concluded from the above results that the ??-ALAD activity is found to be an indicator of the total metal ion concentration in the blood, and therefore, is considered to be of doubtful value as a biological index of lead exposure for screening large population of lead workers.
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