The in vitro effect of metal ions on the activity of erythrocyte delta-aminolevulinic acid dehydratase.

The effects of a total of 15 metals on the activity of erythrocyte delta-aminolevulinic acid dehydratase (ALA-D) were investigated in vitro. The degree of inhibition of the ALA-D activity by copper, tin, mercury and silver was almost equal to that by lead, when the metal was added to the hemolysate of whole blood at the concentrations of 0.1 to 1.0 mmol/l in the ALA-D assay. Magnesium, manganese and beryllium had no effect on the ALA-D activity at the same concentrations. Zinc had a mild activating effect on ALA-D at the optimum concentrations and it eliminated the inhibitory effect of lead to some extent. However, the inhibitory effects of both mercury and cadmium on ALA-D were not quite eliminated even by the addition of zinc. These facts seem to suggest that the inhibition mechanism of lead on ALA-D differs from those of other metals.