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The oxidative cleavage of folates

1978; Elsevier BV; Volume: 84; Issue: 1 Linguagem: Inglês

10.1016/0003-2697(78)90511-0

1096-0309

Tadashi Maruyama, T. Shiota, Carlos L. Krumdieck,

Biopolymer Synthesis and Applications

Alkaline permanganate oxidation has been used to determine the chain length of naturally occurring pteroylpolyglutamates on the assumption that all forms of folates cleave at the C9N10 bond to produce the corresponding p-aminobenzoyl-polyglutamates. The chain length of the latter could be determined by cochromatography with synthetic markers. The products of alkalinc (ammonium bicarbonate buffer, pH 9.0) permanganate oxidation of a number of reduced and oxidized, one-carbon-substituted and unsubstituted folic acid derivatives have been identified, and their yields and stability to the oxidative treatment have been determined. Unsubstituted, oxidized and reduced folic acid and N5-formyl-tetrahydrofolic acid are cleaved at the C9N10 bond to produce p-aminobenzoylglutamic acid. N5, N10-methenyl-tetrahydrofolic acid, N5,N10-methylene-tetrahydrofolic acid, and N10-formyl-tetrahydrofolic acid are not cleaved but are oxidized to N10-formyl-folic acid which is completely stable to the oxidative treatment employed. N5-methyl-tetrahydrofolic acid is not cleaved either but is oxidized to N5-methyl-dihydrofolic acid which upon continued oxidation decomposes slowly to unidentified products. The γ-glutamyl peptide linkage is completely stable to oxidation. Using p-amino-[3,5-3H]benzoylglutamic acid, it is also shown that this product, previously thought to be stable to the oxidative treatment is decomposed by it. The significance of these findings in terms of the errors that may have been introduced in prior estimations of the chain length and pool sizes of the naturally occurring pteroylpolyglutamates is discussed. The possibility of developing a method for the chain length determination of noncleavable pools of one-carbon-substituted folates using [2-14C]folic acid to label the folates in vivo is presented.