Which vitamin is required for the rate-limiting step of heme synthesis:: (A) Vitamin B1, (B) Vitamin B2, (C) Vitamin B3, (D) Vitamin B6
Answer is D. The rate-limiting step of heme synthesis is catalysed by ALA synthase This condensation reaction requires Pyridoxal phosphate (Vitamin B6) as a cofactor. This is why vitamin B6 deficiency leads to sideroblastic anemia.