STUDIES ON THE FEULGEN REACTION WITH HISTOCHEMICAL MODEL SYSTEMS

The absorption spectra of Feulgen-stained deoxyribonucleic acid (DNA)-containing membranes have been studied under various conditions. The absorption curve of the Feulgen-stained DNA-cellulose differs from those of the other model systems and is comparable to that of a solution of apurinic acid stained by the Schiff reaction. The spectral shift caused by the reaction of formaldehyde and SO 2 with the stained films was used as a criterion for the degree of substitution of the bound pararosaniline. The spectrum of DNA-cellulose, unlike the spectra of the other models, did not show any change under the action of these reagents. This indicates that the three amino groups of pararosaniline are all bound to the DNA in a stained DNA-cellulose film. When the mobility of the apurinic acid chain is restricted, the formation of the trisubstituted product is apparently hindered. Such a situation may be present in DNA-containing polyacrylamide films containing proteins and also in cell nuclei. From a study of the literature it is concluded that the shoulder in the pararosaniline spectrum is most probably caused by a configurational isomer of the dye as indicated by Lewis et al. (16) for crystal violet. To explain the abnormal spectrum of the stained DNA-cellulose, it is proposed that in this case pararosaniline is bound with the three amino groups to three neighbouring deoxyribose groups in the hydrolyzed DNA. Studies with Stuart models of the molecules involved showed that in this case one conformation isomer of pararosaniline can be constructed more easily than the other. This situation may explain the spectrum of the stained DNA-cellulose. The other spectral results could also be interpreted on basis of this hypothesis.