Permissive Effects of Hormones on the Induction of δ-Aminolevulinic Acid Synthase in Cultured Chick-Embryo Liver Cells

Abstract

The biosynthesis of heme is regulated by the activity of the first enzyme of its biosynthetic pathway, δ-aminolevulinic acid synthase (ALA-S) (4). This enzyme is present in the mitochondria and is inducible in the liver by a variety of compounds of hydrophobic nature. Studies of the regulation of ALA-S have been facilitated by the introduction of a tissue-culture technique for cultivating monolayer of chick-embryo liver cells (2). A major drawback of this system, however, has been the variability of hormone content of fetal bovine serum, which is used to supplement the culture medium. In addition, the presence of heme in such sera has also been shown to be inhibitory to the formation of ALA-S (3). In the present study, we report that chickembryo liver cells can be cultivated in a completely chemically defined medium, thus allowing detailed studies on the mechanism of hormone action in these cells. Utilizing this culture method, the permissive effect of insulin, hydrocortisone and triiodothyronine on the induction of ALA-S has been demonstrated.