Activation of delta-aminolevulinic acid dehydratase following donation of zinc from kidney metallothionein.

Metallothionein has been postulated to function in essential metal homeostasis. In this study, we demonstrate a 1.7-fold increase in purified bovine liver delta-aminolevulinic acid dehydratase (ALAD) activity following incubation with purified kidney Zn-thionein isolated from Zn-treated rats. The mechanism of enzyme activation, as demonstrated using 65Zn-labeled thionein, involves direct transfer of Zn from Zn-thionein to ALAD. These data support the hypothesis that metallothionein serves to regulate the intracellular bioavailability of essential cations, functioning as a reservoir or conduit through which metals are donated to enzymes which require them as cofactors.