Sites of heme synthesis are all of these except:

Ans. a. RBC (Ref: Harper 30/e p325)Heme biosynthesis occurs in most mammalian cells except mature erythrocytes, which lack mitochondria."Heme biosynthesis occurs in most mammalian cells with the exception of mature erythrocytes, which do not contain mitochondria. However, approximately 85% of heme synthesis occurs in erythroid precursor cells in the bone marrow and the majority of the remainder in hepatoeytes. "- Harper 30/e p325Heme biosynthesisHeme biosynthesis occurs in most mammalian cells with the exception of mature erythrocytes, which do not contain mitochondriaQ.Sites: 85% of heme synthesis occurs in erythroid precursor cells in the bone marrow, and the majority of the remainder in hepatocytesQ.The enzymatic process that produces heme is properly cailed porphyrin synthesis. In humans, this pathway serves almost exclusively to form heme.The pathway is initiated by the synthesis of D-Aminolevulinic acid (dALA or 6ALA) from amino acid glycine & succinyl- CoA from the citric acid cycle (Krebs cycle) Q.Rate-limiting enzyme responsible for this reaction, ALA synthase, is negatively regulated by glucose & heme concentrationQ.It involves both cytoplasm & mitochondriaQHemes are most commonly recognized as components of hemoglobin, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochrome, catalase & endothelial nitric oxide synthaseQ.