Some Quantitative Aspects of the Feulgen Reaction for Desoxyribose Nucleic Acid

Abstract

The Feulgen reaction was tested on purified prepns. of desoxyribose nucleic acid (DNA). The procedure was to add 5 cc. of a 20% gelatin sol to small test tubes containing DNA. Drops of the warm gelatin-DNA prepns. were then placed on glass slides and allowed to gel. The gelatin drops were hardened in 6% formalin for 1-1/2 hrs. and washed in tap water for 2-3 hrs. Prepns. containing DNA at 0.2, 0.5, 0.8, 1, 1.5, 2, and 3 mg./cc. were tested. One drop of each prepn. plus 2 or more DNA-free drops were placed on a slide. The slides were hydrolyzed in 1[image] HCl at 55[degree] C for 3-39 min. and immersed for 1-1/2 hrs. in leuco-fuchsin reagent. Color estimations were made after a rinse in dist. water and 2 changes of water saturated with SO2. No color was developed with small amts. of DNA, while in the middle range the color increased to a maximum. With higher concns. of DNA there was no change in color intensity after periods of hydrolysis beyond those needed for max. color development. The Feulgen reaction is quantitative only over a short range of DNA concns. At least 0.8 mg./cc. of DNA must be present to produce color. Beyond 1.5 mg./cc. the color does not intensify after a 15 min. hydrolysis.