[NAD participation in protecting DNA from damaging factors]

It was found that autolytic degradation of DNA during the isolation of nuclei under conditions of an in situ stimulated NAD biosynthesis is decreased to 2.5% in comparison with 5.2% in control. The increase in the NAD-pyrophosphorylase activity and the intranuclear content of NAD was almost 3-fold, whereas the amount of the acid-soluble DNA material was decreased 2-fold. The degree of DNA damage was increased up to 23% after induction with ethidium bromide. Under these conditions a preliminary in vivo stimulation of NAD biosynthesis by nicotinamide diminished the amount of the acid-soluble material. The levels of intranuclear NAD as well as the NAD-pyrophosphorylase and poly-(ADP-riboso)polymerase activities were essentially affected.