Metal inhibition of ferrochelatase activity in human lymphocytes.

The activity of the terminal enzyme of haem biosynthesis, ferrochelatase (EC 4.99.1.1) was measured in sonicates of human lymphocytes. We used a sensitive method with zinc and mesoporphyrin as substrates and quantification of the product zinc-mesoporphyrin by HPLC. A variety of metal ions and organometal compounds were examined as possible inhibitors of ferrochelatase activity. Inhibition was observed with copper and mercury (but not with lead) and with tributyltin and methylmercury. The kinetics of ferrochelatase inhibition were examined for each of the four inhibitors identified.