Enzyme kinetic analysis of DNA cleavage site induced by ultrasoft X- and cobalt-60 -rays

Akamatsu, Ken

Low-energy electrons emitted from DNA constituent atoms after irradiation with ultrasoft X-rays (USX) have been suggested to tend to form severe DNA damage. The aim of this study is to clarify the difference of DNA damage such as a cleavage pattern directly induced by USX from that by Co-60 -rays. USX- irradiation was performed using a beamline BL23SU at SPring-8. To characterize the cleavage sites, digestion velocity of the irradiated DNA pretreated with or without calf intestinal alkaline phosphatase by snake venom phosphodiesterase (SVPD) was measured. SVPD is an exonuclease producing a deoxynucleoside-5'-monophosphate one after another from a 3'OH terminal. The alkaline phosphatase treatment enables some of the SVPD-resistant sites to be digestive by SVPD. The initial digestion velocity is expected to give us information about the cleavage sites such as the amount, the chemical structure and the degree of overhang at the dsb sites. In this presentation, we will discuss variations of DNA cleavage produced by ionizing radiations, suggested by the experiments based on enzyme reaction kinetics.