<prompt> The regulating enzyme in heme synthesis isALA synthaseALA dehydrataseFerrochelataseProtoporphyrin  <response>: ALA synthase 276-Lippencotts 3rd 210- U.S.3rdBiosynthesis of heme - The major sites of heme biosynthesis are the liver, which synthesizes a number of heme proteins particularly, cytochrome P450 and the erythrocyte-producing cells of the bone marrow, which are active in hemoglobin synthesis. ALA-synthase is the rate controlling step in hepatic porphyrin biosynthesis 276-LP The first committed step in heme biosynthesis catalyzed by 5-aminolevulinate ALA synthase is regulatory. Heme or its oxidized product hemin Fe controls this enzyme activity by three mechanisms.1. Feedback inhibition2. Repression of ALA synthatase3. Inhibition of transport of ALA synthase from cytosol to mitochondria the site of action 21.5-U Satyanarayan 2nd ALA synthase is main rate-limiting enzyme in the synthetic pathway 469-Chatterjee Shinde 6th ALA dehydratase is second rate-limiting enzymeRate limiting Enzymes1. Fatty acid synthesisAcetyl Co A carboxylase2. Cholesterol synthesisHMG-Co A reductase3. Bile acid synthesis7 a-hydroxylase4. Prostaglandin synthesisPhospholipase A25. Uric acid synthesisXanthine oxidase6. Catecholamine epinephrineTyrosine hydroxylase tyrosinase 