Comparative studies of Feulgen hydrolysis for DNA

Summary

We compared the Feulgen hydrolysis curves (37° C, 5 M HCl) of human blood lymphocytes fixed by the following four methods: 96% ethanol, 60 min at 20° C; ethanol-acetone, 1∶1, 120 min at 4° C; ethanolglacial acetic acid mixture (3∶1), containing 2% of formaldehyde (EAF), 90 min at 20° C; and ethanol-glacial acetic acid (3∶1), 60 min followed by 5% chrome alum solution for 360 min at 20° C. The best results were obtained with EAF-fixation, with respect to the highest amount of DNA-Schiff complex at the peak point of the curve, the longest “plateau” region and the smallest scattering of DNA-Schiff amount values along the “plateau”. With other types of fixation the addition of polyethylene glycol (PEG) 6,000 to the hydrolysis solution resulted in modification of the shape of the hydrolysis curve so that it became nearly similar to the EAF-curve. The effect of PEG₆₀₀₀ on the EAF-curve was minimal. Slides fixed by ethanol were used for a comparison of polyethylene glycols with m.w. 1,500, 6,000 and 20,000. The longest “plateau” was obtained with PEG₆₀₀₀. The only effect of PEG₁₅₀₀ was a dramatic increase of DNA-Schiff amount at the peak point. PEG₂₀₀₀₀ had no significant effect on the shape of the hydrolysis curve. The results are discussed in terms of Kjellstrand's “chain with a stable structure” model of Feulgen hydrolysis.