The intracellular distribution of free nucleotides in the tobacco leaf. Formation of adenosine 5'-phosphate from adenosine 5'-triphosphate in the chloroplasts.

1. A method of studying the free nucleotides of leaf tissue is outlined and the need for a metal ion-binding agent for the complete extraction of certain nucleotides by aqueous ethanol is established. 2. The method was used to study the effect of illumination or darkening of tobacco plants on the free nucleotides present in the chloroplast and non-chloroplast tissue components. 3. When plants that had been in the dark for a prolonged period were given 30sec. of bright light there was a rapid phosphorylation of ADP to ATP in both chloroplast and non-chloroplast components of the tissue. 4. Where plants were moved into the dark from conditions suitable for rapid photosynthesis there was a rapid conversion of ATP into AMP and the AMP was formed only in the chloroplast fraction. In continuing darkness the AMP remained restricted mainly to the chloroplast fraction for at least 2min., but eventually its concentration fell to the low value that is typical of tobacco leaves during conditions of constant illumination. If the plants were returned to the light for 30sec. the AMP was rapidly rephosphorylated.