Evidence of the induction of de novo synthesis of delta-aminolaevulinate dehydratase by lead.

Inhibition of delta-aminolaevulinate (ALA) dehydratase (porphobilinogen synthase: EC 4.2.1.24) coupled with an increase in the enzyme concentration was observed in the liver of rats exposed to lead by mouth for 150 days. ALA dehydratase concentration increased by 25% in rats exposed to lead and cell free translation also showed an increase in de novo synthesis of ALA dehydratase by 20% in the liver of rats exposed to lead. The addition of lead in vitro to the cell free translation system had no effect on the de novo synthesis of ALA dehydratase. These results suggest that exposure to lead caused a transcription dependent induction of ALA dehydratase which might compensate for the enzyme inhibition by lead.