The induction in vitro of the synthesis of delta-aminolevulinic acid synthetase in chemical porphyria: a response to certain drugs, sex hormones, and foreign chemicals.

1. A method is described for the primary growth of chick embryo liver cells on cover slips in culture, and the factors of the culture medium are considered that affect the induction of porphyrin formation with certain chemicals. 2. A method is described for following &aminolevulinic acid synthetase (ALA synthetase) activity by the determination of porphyrin fluorescence developed in the cells on cover slips after induction with chemicals or drugs. 3. A nonchromatographic method is described for the determination of b-aminolevulinic acid and aminoacetone in the range of 10-s mole. 4. With allylisopropylacetamide as inducing chemical, an &fold increase in the mitochondrial ALA synthetase of chick embryo liver has been found. No other tissue tested was inducible. 5. After induction, porphyrin increased at almost a logarithmic rate for the first 12 hours. 6. The inducing action of the chemical is reversible. 7. The half-life of ALA synthetase in chick embryo liver cells in culture is 4 to 6 hours. 8. The chemicals and drugs which induce a porphyria in the chick embryo liver cells in culture may be separated into four classes: the barbiturates which contain three chemical groups that can individually induce; the collidines which contain two chemical groups; the sex steroids; and a miscellaneous class. 9. Evidence is presented that the control of ALA synthetase in the liver is by feedback repression in which heme may be the corepressor. No feedback inhibition was found. 10. The site for induction is proposed to be a site on a repressor which is competed for by heme and an inducing chemical. 11. Hepatic porphyria is postulated to be caused by a mutation in an operator gene that is poorly responsive to the repressor. The delay in appearance of symptoms of this