Translational inhibition by heme of the synthesis of hepatic δ-aminolevulinate synthase in a cell-free system

Synthesis of δ-aminolevulinate synthase in a rabbit reticulocyte lysate system directed by total polysomes from the liver of allylisopropylacetamide-treated rats was studied with the combined use of [³H]leucine and a specific rabbit antibody. The protein synthesis observed in the cell-free system employed represented mainly the peptide chain elongation and its termination rather than the net synthesis involving initiation. Synthesis of δ-aminolevulinate synthase in this cell-free system was inhibited progressively with the increased addition of hemin; the synthesis was reduced to about 40% by about 30 μM hemin. Synthesis of total protein, however, was not significantly affected by the addition of hemin. The data obtained suggest that heme inhibits a peptide chain elongation step in the synthesis of δ-aminolevulinate synthase.