5,10-Methenyltetrahydrofolic acid

D. R. Robinson, The nonenzymatic hydrolysis of N5,N10-methenyltetrahydrofolic acid and related reactions. 

N -Methyltetrahydrofollc acid A/S-FormyHetral rolblic add (tbiinic acid) N l -Forrnyltetraliydialblic acid Al i -Methenyltetrahydrofolic acid AfS-KlMethylenetetiaiiydroioric acid N -Formiminotetrabydrofolic acid... 

Co-enzymes derived from tetrahydrofolic acid (70) are frequently involved in the biosynthetic transfer of one carbon fragment (usually at the oxidation level of formate, formaldehyde or methanol) and they complement two other cofactors, S-adenosylmethio-nine and methylcobolamine, which are also used biosynthetically for this purpose. Thus the studies which have revealed the metabolic origin of each of the atoms of the purine ring system (65) have demonstrated that carbon atoms 2 and 8 are derived from formic acid, respectively via N -formyltetrahydrofolic acid (71) and N, N -methenyltetrahydrofolic acid (partial formula 72). 

N5,N10-methenyltetrahydrofolate (with ascorbic acid) was adjusted to neutral pH, autoclaved, and stored at -20° C prior to column purification on DEAE and G-15 Sephadex. These labeled products are the biologically active diastereomers, and they are used to study the metabolism of folinic acid in cells, tissues, and animals. 

Photolyases are monomeric proteins of 450—550 amino acids and two noncovalently bound cofactors (Johnson et al, 1988 Joms et al, 1984). One of the cofactors is always FAD. The other cofactor, which is also called the second chromophore, is methenyltetrahydrofolate (MTHF) in the majority of photolyases and 8-hydroxy-7,8-didemethyl-5-deazariboflavm (8-HDF) in a limited number of species (some archaea, Anacystis nidulans, and some ferns that synthesize this cofactor) (Eker et al., 1988, 1990 Johnson et al, 1988 Kiener et al, 1989 Malhotra et al, 1992). 

Folic acid cofactors (1) are derived from tetrahydropteroic acid linked to the a-amino function of poly-y-glutamyl peptides of varying chain length (n = 1-8). The absolute configuration at C-6 for tetrahydrofolate (H4-folate) which should also include the pteroyl polyglutamates, has been defined as (S) by X-ray studies on 5,10-methenyltetrahydrofolate [5]. 

De Brouwer et al. (2010) identified 5 folate vitamers in their study 5-methyltet-rahydrofolate (the predominant vitamer), 5,10-methenyltetrahydrofolate and tetrahy-drofolate (the most labile vitamers), folic acid, and 10-formyl folic acid. This study reported that folate levels in wild-type rice were approximately 20 pg/lOO g lower than in bio-fortified rice [41], While separation of folate vitamers was obtained in 8 min run time, a previous LC-MS/MS method required 20 min [49]. Also, UPLC improved the sensitivity by reducing the limit of quantitation. Another study documented that endogenous 5-methyltetrahydrofolate in bread ranged between 1.3 and 3.4 pg/100 g [14]. Measurements of folic acid and 5-methyltetrahydrofolate in flour and infant milk formula have been successfully made using this method, described in the latter study. 

---