Reduction of delta-aminolevulinate dehydratase concentration by bromobenzene in rats

The effects of bromobenzene on delta-aminolevulinate (ALA) dehydratase (EC 4.2.1.24) were examined in rats. The enzyme in the bone marrow was irreversibly inhibited after 12 hours of treatment with bromobenzene (intraperitoneally) without any change in the enzyme concentration. When bromobenzene treatment was prolonged to 72 hours, the concentrations of the enzyme in the bone marrow and in the liver were reduced proportionally to the decrease in the enzyme activity. Neither the activity nor the concentration of ALA dehydratase in the peripheral erythrocytes were reduced even after 72 hours treatment with bromobenzene. These findings indicate that bromobenzene decreases ALA dehydratase activity in a biphasic manner; firstly, through an irreversible inhibition probably due to the formation of mercaptide with the essential SH groups and, secondly, through a reduced synthesis of the enzyme.