The effect of zinc and pH on the behaviour of delta-aminolevulinic acid dehydratase activity in baboons exposed to lead.

Four adult male baboons (Papio ursinus) were exposed to a cloud of lead oxide dust to induce changes in the status of delta-aminolevulinic acid dehydratase (ALAD). Enzyme activity fell rapidly to a steady state as blood lead levels rose above normal. Exogenous zinc was shown to activate the enzyme, and the antagonistic effect of zinc on in vivo and in vitro lead inhibition was demonstrated for baboons. In baboons not exposed to lead dust, ALAD showed an activity optimum at pH 7-1 which shifted to pH 6-8 with in vitro addition of lead. In baboons exposed to lead dust, with raised blood lead, activity optima were observed at pH 6-8 and 6-2, while the optimum at pH 7-1 was absent.