Effects of sterol manipulation on microsomal desaturase activities in Tetrahymena: with regard to thermal acclimation

The role of NH+4 ion and AMP deaminase reaction in the activation of phosphofructokinase with respect to its response to the adenylate energy charge was investigated using permeabilized yeast cells. (a) Phosphofructokinase and AMP deaminase were activated by the decrease in the adenylate energy charge. The addition of NH+4 further stimulated the phosphofructokinase activity in the presence of intracellular level of K+, and the optimal energy charge value giving the maximal response of the enzyme was shifted from 0.3 to the value above 0.5. (b) The increase in NH+4 ion produced through the activation of AMP deaminase by spermine which shows no direct action on the phosphofructokinase activity can activate phosphofructokinase with shift of the optimal energy charge value of the enzyme to 0.5 in the presence of K+, whereas the optimal energy charge value for AMP deaminase reaction was not affected by the addition of spermine. Phosphofructokinase can be activated most effectively by the physiological decrease in the energy charge under the condition of increased NH+4 in the presence of K+. The possibility that the interaction of phosphofructokinase with AMP deaminase under hypoxic condition might be a contributing factor to the Pasteur effect is discussed.