Synthesis of Diphosphopyridine Nucleotide in Irradiated Rats

Abstract

WHEN suspensions of nuclei from thymus or spleen are incubated in vitro, adenosine monophosphate in the nuclei is phosphorylated to the triphosphate¹. This phosphorylation appears to be abolished following low doses of X- or γ-radiation, given either in vitro or in vivo ². However, the net synthesis of diphosphopyridine nucleotide in vivo following intraperitoneal injection of 0.5 gm. nicotinamide/kgm. (ref. 3) was not abolished when rats were exposed to X-radiation in doses up to 1,500 r. 3–60 min. before nicotinamide injection (Table 1); in these experiments, the pyridine nucleotide content of the tissue extracts was measured by the alcohol dehydrogenase method⁴. Since the synthesis of this nucleotide is restricted to the nucleus of the cell⁵ and requires adenosine triphosphate⁶, the above result suggests that appreciable amounts of adenosine triphosphate are still available to the cell nuclei during the first two or three hours after irradiation.