Feulgen-DNA absorption spectrum of euchromatin and constitutive heterochromatin.

When the heterochromatin and euchromatin of Triatoma infestans are maximally depurinated, their Feulgen-DNA spectral profiles exhibit a shoulder at about lambda = 530 nm. The shoulder is especially prominent in the curves of the heterochromatin. It is assumed that this pattern is related to richness in repetitive DNA in the heterochromatin, favoring appearance of Schiff reagent molecules di-substituted with adjacent apurinic acid aldehydes.