Studies on the Energy Metabolism of Human Leukocytes II. Mechanism of the Pasteur Effect in Human Leukocytes

1. The control of glycolysis by respiration in normal human leukocytes was studied under conditions in which a Pasteur effect was present and under conditions in which this effect was lost.

2. There was a 20-50 per cent Pasteur effect in leukocytes isolated by dextran sedimentation of heparinized blood and suspended in isologous serum. Crossover point analysis of glycolytic intermediates indicate that phosphofructokinase becomes rate-limiting for aerobic glycolysis and that this enzyme is primarily responsible for the Pasteur effect.

3. Studies on the activity of PFK in leukocyte homogenates showed that this enzyme is competitively inhibited by ATP and reactivated by ADP and Pi. The concentrations of these compounds which significantly effect PFK activity in homogenates fall within the range found in intact cells. The differences in PFK activity in intact cells under anaerobic and aerobic conditions can therefore be attributed to allosteric effects caused by an increase in the concentration of ATP on transition to aerobic conditions, with concomitant decreases in the levels of ADP and Pi.

4. Leukocytes isolated by the same procedure but suspended in an artificial medium rather than serum did not show a Pasteur effect. There were no differences between the aerobic and anaerobic concentrations of ATP, ADP, and Pi, and there was no control point at PFK. It is suggested that a change in respiratory function is responsible for the altered control of glycolysis in leukocytes suspended in nonserum media.