Preparation of32P-labelled adenosine triphosphate

In experiments on the metabolism of adenosine triphosphate (ATP) it became desirable to use the 32P-labelled compound. ATP labelled with 32p has been isolated from 'the rabbit after injection of radioactive phosphorus by Dounce, Rothstein, Beyer, Meier & Freer (1948), but the specific activity of the product was too low to be of much further experimental use. Therefore a laboratory method of preparing this substance quickly in small quantities of high specific activity was elaborated. It is based on the observation that ATP readily exchanges the two terminal phosphate groups only when incubated with inorganic phosphate in respiring tissue suspensions (Krebs, Ruffo, Johnson, Eggleston & Hems, 1953). In the presence of 32pO4 such sus- pensions convert added ATP in 0-0025M solution, within about 20 min. incubation, into ATP equally labelled in the two termninal phosphate groups. The active material can be recovered as barium salt and purified by paper chromatography.