Increase of fructose-1,6-diphosphatase activity in cultured human peripheral lymphocytes and its suppression by phytohemagglutinin.

The specific activity of fructose-1,6-diphosphatase in freshly isolated human peripheral lymphocytes is usually less than 10% of what can be found in normal animal livers. The enzyme activity is strongly inhibited by AMP and is also inhibited by its substrate, fructose-1,6-diphosphate, at concentrations higher than 20 μM. In cultured lymphocytes the enzyme activity gradually increases so that by day 3 of the incubation the specific enzyme activity could be 15 to 80 fold higher than the preincubation level. The increase would continue for at least 10 days if the culture medium is periodically renewed. When phytohemagglutinin is present in the culture medium, the increase of the enzyme activity is completely suppressed. No free soluble enzyme inhibitor could be detected in phytohemagglutinin-treated cells by mixing and dialysis experiments.