[X-ray diffraction study of polymorphism of the DNA double helix at protonation]

X-ray diffractograms of DNA fibers have been obtained at various degrees of protonation (alpha). At the protonation degrees preceding acid denaturation, DNA double helix undergoes polymorphic transformation. At 75% relative humidity DNA helix of 11 : 1 type protonated up to alpha = 0.3 changes to 10 : 1 type.