Hydroxymethyl tetrahydrofolic acid

Extracts of cells - of Escherichia coli infected with a T-even bacteriophage contain an enzyme deoxycytidylate hydroxymethylase which is not detected in uninfected cells it catalyzes the formation of 6 -(hydroxymethyl)-2-deoxyc3didylic acid from formaldehyde and 2-deoxycytidyUc acid in the presence of tetrahydrofolic acid and magnesium ions. In a large-scale experiment, 10.6 mg. of the barium salt was prepared. 

Folic acid or the folate coenzyme [6] is a nutritional factor both for the parasites and the hosts. It exists in two forms, viz. dihydro- and tetrahydrofolic acids [4,5] which act as cofactors involved in the transfer of one carbon units like methyl, hydroxymethyl and formyl. The transfer of a one carbon unit is associated with de novo synthesis of purines, pyrimidines and amino acids. Mammals can not synthesize folate and, therefore, depend on preformed dietary folates, which are converted into dihydrofolate by folate reductase. Contrary to this, a number of protozoal parasites like plasmodia, trypanosomes and leishmania can not utilize exogenous folate. Consequently, they carry out a de novo biosynthesis of their necessary folate coenzymes [12]. The synthesis of various folates follows a sequence of reactions starting from 2-amino-4-hydroxy-6-hydroxymethyldihydropteridine (1), which is described in Chart 4 [13,14]. 

Tetrahydrofolic acid and conjugates IVansfer of formyl, hydroxymethyl and methyl groups Folic acid... 

Tetrahydrofolic acid (THF) holds a central position in one-carbon metabolism. Formyl groups, hydroxymethyl, and methyl groups may be transferred via the THF derivatives given in Table 16. 

In the formation of tetrahydrofolic acid 6-hydroxymethyl-7,8-dihydropterin pyrophosphate condenses with p-aminobenzoic acid (D 8.2) to dihydropteroic acid. This compound reacts with glutamine in the presence of ATP to dihydro-folic acid from which folic acid as well as tetrahydrofolic acid may be formed. 

Tetrahydrofolic acid which was found to be a coenzyme acceptor of a single carbon unit for the conversion of serine to glycine also reacts with formaldehyde chemically to form a derivative which can serve as an enzymatic donor of an hydroxymethyl group -. Studies on the formaldehyde binding... 

In enzymic reactions, the active form of folic acid is generally considered to be a derivative of 5,6,7,8-tetrahydrofolic acid (FH ) which reversibly forms formyl or hydroxymethyl compounds for participation in singlecarbon transfer reactions (S, S). The formyl or hydroxymethyl group in the coenz3one is usually assumed to be attached to the nitrogen in position 10 from which point either group can reversibly form a bridge to position 5. 

Folic acid (Fig. 6) is the precursor of a number of coenzymes vital for the synthesis of many important molecules. These derivatives of folic acid, referred to collectively as active formate and active formaldehyde , are responsible for the donation of one carbon fragments in the enzymatic synthesis of a number of essential molecules. In the formation of methionine from homocysteine, the folic acid coenzyme donates the S-methyl group, and in the conversion of glycine to serine it is necessary for the formation of the hydroxymethyl group. Folic add is converted into its active coenzyme forms by an initial two step reduction to tetra-hydrofolic add (Fig. 6) by means of two enzymes, folic reductase and dihydrofolic reductase. Conversion of tetrahydrofolic acid (THF) to an active coenzyme folinic acid subsequently occurs by ad tion of an Ns formyl group (Fig. 6). The formation of similar compounds such as an Nio formyl derivative, or the bridged Ns,Nio-methylenetetrahydrofolic acid, also leads to active coenzymes. 

A subclass of lyases, involved in amino acid metabolism, utilizes pyridoxal 5-phosphate (PLP, 3-hydroxy-2-methyl-5-[(phosphonooxy)methyl]-4-pyridinecarbaldehyde) as a cofactor for imine/ enamine-type activation. These enzymes are not only an alternative to standard fermentation technology, but also offer a potential entry to nonnatural amino acids. Serine hydroxymethyl-tansferase (SHMT EC 2.1.2.1.) combines glycine as the donor with (tetrahydrofolate activated) formaldehyde to L-serine in an economic yield40, but will also accept a range of other aldehydes to provide /i-hydroxy-a-amino acids with a high degree of both absolute and relative stereochemical control in favor of the L-erythro isomers41. 

Significant HMBPA accumulation indicates a metabolic bottleneck at the PanB-catalyzed hydroxymethylation step. Engineering the supply chain for methylene tetrahydrofolate, the cosubstrate of the PanB reaction, by overexpression of SerA and GlyA or of the enzymes of the glycine cleavage cycle drastically reduced HMBPA accumulation in favor of further increased (7 )-pantothenic acid production [177]. This result indicates that insufficient availability of the PanB cosubstrate is a major cause of unwanted side-product formation. 

The biochemically active form of folic acid is 5,6,7,8-tetrahydrofolic add (FH4), a coenzyme in the metabolism of one carbon units. Hydroxymethyl and formyl groups are carried on atoms N5 and NIO of FH4. For example, when the amino add, l-... 

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