The site of action of four metals (copper, lead, nickel and zinc) on the aminolevulinic
acid dehydratase of human erythrocytes was studied. Data obtained after dénaturation of
allosteric sites with heat treatment and after simultaneous incubation with two metals suggest the
following conclusions: copper acts on the catalytic site, whereas lead, nickel and zinc act on the
allosteric sites; zinc and nickel act on the same allosteric (metallic) site; zinc and lead only partially
act on the same metallic site; nickel and lead act on different allosteric sites.