Effect of zinc ions on δ-aminolevulinate dehydratase in Ustilago sphaerogena

Abstract

The activity of δ-aminolevulinate dehydratase (E.C. 4.2.1.24) in crude extracts of the smut fungus Ustilago sphaerogena, grown in its sporidial stage, has been found to depend on the concentration of Zn ++ in the culture media; half-maximal effect was at about 2 × 10 −6 M. Dialysis of crude extracts did not result in the loss of enzyme activity, which might be expected if the enzyme is activated by reversible enzyme-Zn ++ complex formation, and addition of Zn ++ in vitro had little effect up to 10 −5 m. Higher concentrations of Zn ++ were inhibitory in accord with the implication of essential SH in this enzyme as revealed by inhibition with Cu ++ or iodoacetate. Attempts to obtain highly active enzyme by the addition of Zn ++ to crude extracts from zinc-deficient cells were unsuccessful. The increase in the activity caused by the addition of Zn ++ (3 × 10 −5 m) to a culture previously grown in the presence of low concentration of Zn ++ (10 −7 m) was effectively inhibited by simultaneous addition of p-fluorophenylalanine (4.5 × 10 −4 m), but little inhibition was observed when actinomycin D (200 mg/ liter) was substituted for the amino acid analogue. Thus it appears that Zn ++ is required for the synthesis of this enzyme protein at the translation level.