Pyridoxine Heme synthesis

Pyridoxine (B ) Pyridoxal-P (PLP) Aminotransferases (transaminase) AST (GOT), ALT (GPT) 8-Aminolevulinate synthase Protein catabolism Heme synthesis MCC isoniazid therapy Sideroblastic anemia Cheilosis or stomatitis (cracking or scaling of lip borders and corners of the mouth) Convulsions... 

Answer D. Sideroblastic anemia in a person being treated for tuberculosis (with isoni-azid) is most likely due to vitamin deficiency. 6-Aminolevulinate synthase, the first enzyme in heme synthesis requires vitamin Bj (pyridoxine). 

Defective erythropoiesis (dyserythropoiesis) impaired hemoglobin synthesis leading to lack of utilization and consequent accumulation of iron in mitochondria, e.g., from inhibition of ALA synthase activity by dietary vitamin 85 deficiency inhibition of heme synthesis by lead impairment of pyridoxine metabolism in alcoholic patients familial sideroblastic anemias and Cooley s anemia. 

General metabolic significance. Pyridoxine dependent enzymes catalyze almost exclusively reactions of amino acid metabolism, also participating in heme synthesis and generation of biogenic amines. 

The observations made in oxaluric patients suggest that the lithiasis that pyridoxine-deficient cats develop might be related to the role that pyridoxine plays as a cofactor of the transaminase. Anemia developing in pyridoxine-deficient animals probably can be explained at least in part by an interference with heme synthesis. Indeed, heme synthesis is reduced to one-third of normal in reticulocyte-rich blood obtained from pyridoxine-deficient animals. The rate of heme synthesis reaches normal values when pyridoxal phosphate is added to the incubation medium. This effect... 

Substrate and energy source for synthesis of 6-aminolevulinate in the heme pathway. Converted to glutamate in a reaction requiring the coenzyme form of pyridoxine (Bg)... 

Sideroblastic anemia is characterized by excessive iron in the cells that cannot be incorporated into porphyrin to form heme. Although it is rare, the most common cause of sideroblastic anemia is alcoholism and pyridoxine deficiency. Pyridoxine is required for the formation of pyri-doxal phosphate, a coenzyme in porphyrin synthesis. 

---