Differential inhibition of hepatic ferrochelatase by the isomers of N-ethylprotoporphyrin IX

The four isomers of N-ethylprotoporphyrin IX have been synthesized. The two isomers with the N-ethyl group on pyrrole rings A or B inhibit rat liver ferrochelatase as effectively as the corresponding N-methyl analogues, whereas those with the N-ethyl moiety on rings C or D are 30–100 times less effective. The ability of N-alkyl porphyrins to inhibit ferrochelatase thus depends not only on the size of the N-alkyl group but also on its precise location on the porphyrin face.