Adenine and hypoxanthine metabolism in phythohemagglutinin-stimulated and unstimulated human lymphocytes.

The uptake and subsequent metabolism of adenine and hypoxanthine in phytohemagglutinin-stimulated and unstimulated peripheral human blood lymphocytes, freshly prepared or cultured, were studied. To investigate the initial step of nucleic acid metabolism the incorporation of 14C-purines into the acid soluble material was examined. No preferential uptake of adenine or hypoxanthine was observed in freshly prepared and cultured lymphocytes during an incubation of 1 h. However, cultured cells utilized approximately 1/3 of the purines compared to freshly drawn cells. Within the cells 2/3 of adenine and 1/2 of hypoxanthine were metabolized to nucleotides (mainly AMP and ADP). Incubation of lymphocytes with PHA for 1 h produced in the freshly prepared cells an increase of adenine- and hypoxanthine-uptake to 191% and 153%, in 48 h stimulated cells to 158% and 132%. There was, however, no change in the relative rates of the metabolic routes though the intracellular concentrations of nucleotides formed increased with adenine as substrate to 152% and with hypoxanthine to 161% during a 1 h stimulation. In contrast no enhanced formation of acid soluble nucleotide formation could be observed with PHA stimulation during 48 h. The increased rates of purine uptake and metabolism apparent 1 h after addition of mitogen may be due to an altered transport mechanism at the beginning of the transformation as an adaptive response to the increased requirements for the synthetic processes soon to follow. Once the lymphocytes are transformed no demand of purines is necessary and the uptake and metabolism is switched off.