N10-formyl tetrahydrofolate

N5-Formyl tetrahydrofolic acid, 25 803 N10-Formyl tetrahydrofolic acid, 25 801 Fornacite, 6 4 7 It... 

The atoms of a purine are contributed by amino acids (aspartic acid, glutamine, and glycine), CO2, and N10-formyl tetrahydrofolic acid. 

The amino group of glycine is formylated, with the formyl group being donated by N10-formyl-tetrahydrofolate. 

The effects of cobalamin deficiency are most pronounced in rapidy dividing cells, such as the erythropoietic tissue of bone marrow and the mucosal cells of the intestine. Such tissues need both Die N5-N10-methylene and N10-formyl forms of tetrahydrofolate for Ihe synthesis of nucleotides required for DNA replication (see pp. 291, 301). However, in vitamin B12 deficiency, the N5-methyl form of tetrahydrofolate is not efficiently used. Because the methylated fonn cannot be converted directly to other forms of tetrahydrofolate, tie Ns-methyl form accumulates, whereas the levels of the other forms decrease. Thus, cobalamin deficiency is hypothesized to lead to a deficiency of the tetrahydrofolate forms needed in purine and thymine synthesis, resulting in the symptoms of megaloblastic anemia. 

In living systems, folinic acid can be synthesized ultimately from folic acid by reduction to tetrahydrofolic acid followed by addition of a 1-carbon fragment to the molecule (N5.N1°-methylenetetrahydrofolate, V). After a 2-step oxidation, the formyl group resides either at the N5 or N10 position or as an equilibrium mixture. The essential reactions are summarized below 32... 

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