δ-Aminolevulinate Synthetase of the Chick Embryo Liver: The Effect of Natural and Synthetic Sex Steroids on its Activity

Abstract

δ-Aminolevulinate (ALA) synthetase is the initial enzyme in the porphyrin and heme biosynthetic pathway and catalyzes the formation of ALA from glycine and succinyl coenzyme A. The production of ALA is the rate-limiting step in the hepatic formation of porphyrins and heme (1, 2). The activity of ALA synthetase, as measured by the rate of production of ALA by hepatic mitochondria (1) or homogenate (3) can be markedly enhanced by administration of a large number of chemicals and drugs that induce experimental porphyria in animals (4). In hereditary porphyria of acute intermittent type in man, the activity of this enzyme is also greatly increased (5, 6), which explains, at least in part, the augmented urinary excretion of porphyrins and their precursors, ALA and porphobilinogen, characterizing this disease.