Glycogen synthase kinase-3 inhibition by lithium and beryllium suggests the presence of two magnesium binding sites.

Lithium inhibits (Li(+)) glycogen synthase kinase-3 (GSK-3) by competition for magnesium (Mg(2+)), but not ATP or substrate. Here, we show that the group II metal ion beryllium (Be(2+)) is a potent inhibitor of GSK-3 and competes for both Mg(2+) and ATP. Be(2+) also inhibits the related protein kinase cdc2 at similar potency, but not MAP kinase 2. To compare the actions of Li(+) and Be(2+) on GSK-3, we have devised a novel dual inhibition analysis. When Be(2+) and ADP are present together each interferes with the action of the other, indicating that both agents inhibit GSK-3 at the ATP binding site. In contrast, Li(+) exerts no interference with ADP inhibition or vice versa. We find, however, that Li(+) and Be(2+) do interfere with each other. These results suggest that Be(2+) competes for two distinct Mg(2+) binding sites: one is Li(+)-sensitive and the other, which is Li(+)-insensitive, binds the Mg:ATP complex.