Tetrahydrofolic acid reaction with formaldehyde

P-Hydroxy-a-amino Acids. Another reaction of glycine is catalyzed by pyridoxal. This is the reversible condensation with aldehydes. Glycine and formaldehyde form serine in a model of the reaction observed in biological systems to proceed with tetrahydrofolic acid as a formaldehyde acceptor and donor. When glyoxylate reacts with pyridoxamine, the gly-... 

Side chain cleavage (Group c). In a third type of reaction the side chain of the Schiff base of Fig. 14-5 undergoes aldol cleavage. Conversely, a side chain can be added by (3 condensation. The best known enzyme of this group is serine hydroxymethyltransferase, which converts serine to glycine and formaldehyde.211-21313 The latter is not released in a free form but is transferred by the same enzyme specifically to tetrahydrofolic acid (Eq. 14-30), with which it forms a cyclic adduct. 

One of the most interesting diaminomethanes that has been investigated is a model for the coenzyme tetrahydrofolate (3), a biological one-carbon transfer agent. The mechanism of its conversion into the imidazolidine derivative /V, yV °-methylenetetrahydrofolate (4) has been studied. The pH rate profile apparently results from a change in the rate-determining step with changing acidity. Secondary amines such as morpholine and imidazole catalyze the reaction between tetrahydrofolic acid and formaldehyde via a... 

The N-5 position is considerably more basic than the N-10 position, and this basicity is one of several factors that control certain preferences in the course of reactions involving tetrahydrofolate. Thus, for-mylation occurs more readily at N-10 while alkylation occurs more readily at N-5. Benkovic and Bullard (1973) have reviewed evidence for an iminium cation at N-5 as the active donor in formaldehyde oxidation-level transfers. Recently, Barrows et al. (1976) have further studied such a mechanism for folic acid. The interconversion of these forms of folate coenzymes by enzymatic means has been reviewed by Stokstad and Koch (1967), and the reader is directed there for further details. Folate coenzymes are involved in a wide variety of biochemical reactions. These include purine and pyrimidine synthesis, conversion of glycine to serine, and utilization and generation of formate. In addition, the catabolism of histidine, with the formation of formiminoglu-tamic acid (FIGLU), is an important cellular reaction involving folate. 

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