Radiosensitivity of Nuclear ATP-synthesis

Summary

(1) 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 per cent.

(2) 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.

(3) 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.

(4) ATP-metabolism was studied in vivo using ³²P_i. The curves showing the specific activities of ATP and P_i isolated both from nuclei and from total thymus tissue suggest that at least part of the nuclear ATP is supplied by the cytoplasm.

(5) The incorporation of ³²P_i in nuclear ATP is inhibited by small doses of x-irradiation.