Folin and

The Folin-Denis assay is used as a procedure for the quantification of total phenolics in plant materials, food, and beverages. Reduction of phosphomolybdic-phosphotungstic acid (Folin-Denis reagent) to a blue-colored complex in an alkaline solution occurs in the presence of phenolic compounds (Folin and Denis 1912). 

The colorimetric method based on the reagents of Folin and Denis or of Folin and Ciocalteu has been generally preferred over other methods to determine total phenols in complex natural materials such as wines and fruits (1, 2, 3, 4, 5). This method is relatively simple, convenient, reliable, generally applicable, and it is accepted as an official analysis in several countries for total phenols in wines and a number of other products. Although it is a preferred method, it can be even better than is commonly recognized. 

Tests for the purity of the product were devised by Folin and later improved by Danielson.1 A direct comparison of the two preparations revealed no difference in the degree of purity of the product. 

This purified salt is suitable for use in the procedures of Folin and of Sullivan for the determination of amino acids. 

The biuret reaction (M16), the Folin and Ciocalteu reagent (K22), ultraviolet adsorption (H2) and polarographic determinations (Fig. 25) have also been proposed (B2, H16). 

A colorimetric method for determining mz/o-inositol has been described.104 The color is developed with the phosphomolybdotungstic acid reagent of Folin and Denis, after oxidation of the inositol with bromine. Enzymic methods, based on the inositol dehydrogenases of Acetobacter suboxydans44 and Aerobacter aerogenes,106 have also been used. These methods could be employed with any cyclitol readily attacked by the respective enzyme systems (see pp. 144 and 147). 

The concentrations of phenolic compounds were determinedby HPLC (Waters) using a method described previously by Nilvebrant et al. (21). The total concentration of phenols was also estimated by a spectrophotometric method (23) based on the Folin and Ciocalteu s reagent (Sigma). 

Nitrogen requirements of animals and man. Comments on the Folin and Schoenheimer hypotheses. Proc. Intern. Symposium on Enzyme Chem., Tokyo and Kyoto, 1957, 444 (1958). 

Folin and Ciocalteu s reagent diluted 1 1 with water immediately before use... 

Procedure The alkaline copper reagent was prepared just prior to use by mixing 1 vol. of copper sulphate solution with 1 vol. of sodium potassium tartrate solution followed by 98 vol. of the sodium carbon-ate/sodium hydroxide solution. Alkaline copper solution (5 ml) is added to 100 pA of sample, containing between 20-100 pig of protein, diluted with 900 pil of water. After 10 min 0.5 ml of diluted Folin and Ciocalteus reagent is added. The absorbance at 750 nm is read after 30 min and within 90 min from the final addition. 

Calcium forms used therapeutically include the folinic acid supplement calcium folinate, and the mineral supplements calcium bicarbonate, calcium carbonate, calcium gluconate and calcium lactate. 

Some other colorimetric assays involving diazotization with p-nitroaniline and nitrous acid (34), use of folin and Cioalteu phenol reagent (35), complexation with cupric ion in nitrous acid (36-38) or estimation as the nitro derivative (39) have been reported in the literature. 

A colorimetric method for determination of uric acid was introduced by Folin and Denis (F5) this initial method, which used phospho-tungstate, was modified by a series of investigators (B16, B32, F4). Brown... 

Comparison of the uptake of(III.147) and MTXin cultured L1210 cells [45] confirmed that the quinazoline was able to accumulate to a higher level than MTX when the cells were exposed to the same concentration of drug (4 M) for 40 min. Competitive uptake experiments suggested that (III. 147) shares a common active transport mechanism with MTX and folinic acid. As expected, high concentrations of folinic acid (50 juM) fully protected the cells from the effects of (III. 147). At lower folinic acid concentrations, however, there was only partial protection thus, 5 juM folinic acid (a 100-fold molar excess) was fully protected the cells from 0.05 juM (III. 147), whereas 0.5 /tM folinic acid (only a 10-fold excess) did not. Cells were also completely protected from 0.05 juM (III. 147) with 100 pM thymidine and 100/tM hypoxanthine, and greater protection was achieved with 5 /tM folinic and 100 /iM thymidine than with 5 iM folinic acid alone. It was concluded from these results that (III. 147) does not kill cells solely via DHFR inhibition, but rather via concomitant inhibition of DHFR and TS. 

Despite the overall limitations of these procedures in producing quantitative analyses, certain amino acids that contain appropriate functional groups were readily determined at considerably more sensitive levels by the use of colorimetric methods. Folin and Denis (1912) introduced such an approach to the measurement of tyrosine and tryptophan, and procedures for the determination of arginine (Sakaguchi, 1925), histidine (Koessler and Hanke, 1919 Kapeller-Adler, 1933), and phenylalanine (Kapeller-Adler, 1932) were subsequently reported. The highly reactive thiol group of cysteine has also... 

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