Induction of δ-Aminolevulinate Synthetase in Organ Culture of Chick Embryo Liver by Allylisopropylacetamide and 3, 5-Dicarbethoxy-l, 4-dihydrocollidine

The induction of J-aminolevulinate synthetase [EC 2.3.1.37] by allylisopropylacetamide (AIA) and 3, 5-dicarbethoxy-l, 4-dihydrocollidine (DDC) was studied in a newly devised organ culture of finely chopped chick embryo liver. Both AIA and DDC appeared to stimulate the synthesis of ALA synthetase by acting primarily at the transcriptional level rather than the post-transcriptional level of protein synthesis. The half-life of ALA synthetase induced by AIA in our organ culture system was 2hr, whereas that of the enzyme induced by DDC was as long as 4—5hr. In the chick embryo liver, whether cultured or in ovo, accumulation of ALA synthetase in the cytosol fraction after induction by either AIA or DDC was very small, and the apparent molecular weight of the mitochondrial ALA synthetase from the chick embryo liver was about 250,000 when estimated by gel filtration. Addition of hemin to the culture medium resulted in a considerable inhibition of ALA synthetase induction, probably by interfering mainly with a post-transcriptional spep(s). However, hemin did not cause appreciable accumulation of ALA synthetase in the liver cytosol fraction. Appararently the behaviour of ALA synthetase induction in the chick embryo liver differs in many respects from that in the adult chicken liver.