The key regulatory enzyme in hepatic biosynthesis of heme is

ALA Synthase Is the Key Regulatory Enzyme in Hepatic Biosynthesis of HemeThere are two isozymes of ALA synthase. ALAS1 is expressed throughout the body; ALAS2 is expressed in erythrocyte precursor cells.The reaction catalyzed by ALA synthase 1 is rate-limiting for biosynthesis of heme in liver. It appears that heme, probably acting through an aporepressormolecule, acts as a negative regulator of the synthesis ofALAS1 The rate of synthesis of ALAS1 thus increases greatly in the absence of heme but diminishes in its presence.Heme also affects translation of the enzyme and its transfer from the cytosol to the mitochondrion. ALAS1 has a sho half-life, which is typical for an enzyme that catalyzes a rate-limiting reaction.Reference: Harper biochemistry, 30th edition, page no 326