Biogenesis of mitochondrial proteins regulation of maturation of delta-aminolevulinate synthase by hemin

The effect of hemin on the biogenesis of delta-aminolevulinate (ALA) synthase was examined in primary cultures of chick embryo hepatocytes. Hemin (0.010 mM) in the culture medium significantly inhibited the induction of ALA synthase activity in hepatocytes exposed to the porphyrogenic agent allylisopropylacetamide. In hepatocytes pulse-labeled with [ 35S]methionine for 45 min in the presence and absence of hemin, it was determined by immunechemical analyses that hemin blocked the processing of the precursor of ALA synthase.