Hypothesis: cyclic AMP turnover in S49 cells.

The fractional turnover constant (ke) of cAMP in S49 lymphoma cells stimulated by epinephrine was essentially identical to the decay constant for cAMP in these cells. This was in sharp distinction to the situation in the human diploid lung fibroblast WI-38, in which ke was much lower in hormone stimulated cells. In this study we report a new method for the determination of cAMP turnover. The method was based on the assumption that for tritium label to be incorporated into cAMP on treatment of cells with [3H]-adenine, the label must first pass through ATP. An equation relating the rate of change in cAMP specific radioactivity with cAMP and ATP specific radioactivities was thereby determined. The equation was expressed in a form that gave a linear graphical plot with the fractional turnover constant as the slope of the line.