Radiosensitivity of Nuclear ATP-synthesis

Abstract

Rat thymus nuclei were isolated in a sucrose medium. The cytoplasmic contamination of the nuclear preparations, judged by cytological and enzymatic techniques varied from 4-7%. The nuclear preparations retain considerable amounts of ATP. As a result of incubation of the nuclei without the addition of any substrates, the ATP-content increased. The synthesis of nuclear ATP is a highly radiosensitive process. After irradiation in vivo with x-ray doses ranging from 50-700 r, the ATP-synthesis in isolated nuclei was inhibited. Irradiation of nuclear suspensions in vitro did not inhibit ATP-synthesis. ATP-metabolism was studied in vivo using p32i. The curves showing the specific activities of ATP and P. isolated both from nuclei and from total thymus tissue suggest that at least part of the nuclear ATP is supplied by the cytoplasm. The incorporation of p32^ in nuclear ATP is inhibited by small doses of X-irradiation.