intermediate of kreb cycle used in heme synthesis;

Answer (A) succinyl-CoAAll the carbon and nitrogen atoms of the porphyrin molecule are provided by glycine(a nonessential amino acid) and succinyl coenzyme A (an intermediate in the citric acid cycle) that condense to form ALA in a reaction catalyzed by ALA synthase(ALAS)Heme synthesis also requires a functional tricarboxylic acid cycle and an oxygen supply.Heme synthesis stas in mitochondria with the condensation of succinyl-CoA with the amino acid glycine, activated by pyridoxal phosphate.ALA synthase is the rate-limiting enzyme of heme synthesis. ALA molecules enter the cytoplasm, where their union in the presence of ALA dehydratase yields porphobilinogen(PBG) and water molecules.