Folinic ■ acid, natural

In 1957, Duggan et al.66 reported that maximum natural fluorescence of folinic acid occurred at pH 7, with excitation at 370 nm and emission at 460 nm. 

These are pyrimidine derivatives and are effective because of differences in susceptibility between the enzymes in humans and in the infective organism. Anticancer agents based on folic acid, e.g. methotrexate, inhibit dihydrofolate reductase, but they are less selective than the antimicrobial agents and rely on a stronger binding to the enzyme than the natural substrate has. They also block pyrimidine biosynthesis. Methotrexate treatment is potentially lethal to the patient, and is usually followed by rescue with folinic acid (A -formyl-tetrahydrofolic acid) to counteract the folate-antagonist action. The rationale is that folinic acid rescues normal cells more effectively than it does tumour cells. 

Formyl-tetrahydrofolate is more stable to atmospheric oxidation than folic acid itself and is commonly used in pharmaceutical preparations it is also known as folinic acid and the synthetic (racemic) compound as leucov-orin. Although the [6S, 67 ] racemic mixture might be expected to have only 50% of the biological activity of the naturally occurring 6S isomer, between 10% to 40% of the 67 isomer is biologically active (Baggott et al., 2001). 

The synthesis of folinic acid from fohc acid creates a new asymmetric center at the 6-carbon, and both diastereoisomeric forms tend to crystallize together. Crystallization of the calcium salU from water gives the ZL-form which is about twice as active biologically as the original mixed crystals, and upon conversion to formylfolic acid it does not increase in foUc-like activity for L. casei as does the diastereoisomeric mixture. This /L-diastereo-isomeric form appears to be identical with natural folinic acid. ... 

It is of interest that folic or folinic polyglutamates are required for the conversion of serine to glycine in a cell-free enzyme preparation from a Clostridium strain which apparently cannot utilize monoglutamates, and evidence for the natural occurrence of M -formyltetrahydropteroyltrigluta-mate has been reported . Other bound forms of folinic acid appear to exist. ... 

Another member of the folic acid group of vitamins, citrovorum factor or folinic acid, is also found in natural materials, both in free and combined form. Citrovorum factor is believed to be a metabolically active form of folic acid and is formed in the body from folic acid. The citrovorum content of foods is largely unknown. 

Naturally occurring peptides of the pteroylglutamic acid (PGA) family and of folinic acid, such as p-aminobensoylpolyglutamic acid, are very closely related, by structure as well as by origin, and they may be considered as belonging to the same group. We will therefore discuss them together. 

Citrovorum factor (CF). Synonyms Natural folinic acid. 

Naturally Occurring Peptides of the Folinic Acid Family... 

The older methods for the measurement of protein in natural waters usually depended upon the presence of aromatic amino acids in the protein, and calculated total protein on the basis of an average tyrosine, tryptophan, or phenylalanine content. A method representative of this type was the Folin reagent method published by Debeika et al. [281]. While these methods were useful in fresh water and in some coastal regions, they were not sensitive enough for the lower concentrations to be found in oceanic waters. 

Table 5.6 shows the total phenolic content (determined using the Folin-Ciocalteu assay) and antioxidant activity (ABTS radical scavenging capacity) of extracts from morama bean seed coat and cotyledon prepared with acidified mefhanol. If is clear fhaf morama bean seed coat and cotyledon have appreciable levels of fofal phenolics and antioxidant activity. These phenolics are concentrated in the seed coat. It has been reported that the morama bean cotyledon contains high levels of the amino acid tyrosine (Maruatona et ah, 2010) which is phenolic in nature and can therefore confribufe fo fhe fofal phenolic content of the cotyledon as determined with the Folin-Ciocalteu assay. 

Destroctioii of Viic Acid.—Man and the higher apes have very Kttle power of destroying uric acid compared with that possessed by other mammals, and hence it is the chief end-product of purine metabolism. Folin (1924) reports that 30-70 per cent, of injected uric acid may be destroyed or transformed by the human organism, the nature of the change being obscure. In the dog, at least, the liver is the principal site of uric acid destruction, as shown by the effect of complete hepatectomy which leads to the appearance of large quantities of uric acid, instead of allantoin, in the urine. 

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