Molecular Pharmacology, Vol 11, 70-78, Copyright © 1975 by the American Society for Pharmacology and Experimental Therapeutics

-Aminolevulic Acid Synthetase from Fetal Rat Liver: Studies on the Partially Purified Enzyme

¹ National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709

Hepatic -aminolevulinic acid (ALA) synthetase, the first and, in adults, the rate-limiting enzyme in the heme-biosynthetic pathway, was solubilized and purified 30-fold from 19-day fetal rat liver mitochondria. The properties of the partially purified enzyme were compared with those reported for ALA synthetase preparations from adult rat liver. Fetal and adult enzymes are similar in regard to substrate specificity, pH and temperature optima, and kinetic behavior, but differ substantially in terms of molecular weight, response to high cation concentrations, and regulatory properties. Unlike the adult enzyme, fetal ALA synthetase is not inhibited by the end product, hemin. These results suggest that regulatory differences in ALA synthetase at different stages of development may be due to variations in the biochemical properties of the enzyme in adult and fetal liver. The development of regulatory properties characteristic of the adult enzyme may occur concomitantly with mitochondrial maturation. Pharmacological alterations of the hepatocellular environment during gestation may affect the development of ALA synthetase as the rate-limiting enzyme in hepatic heme biosynthesis.