The effect of temperature on the competitive inhibition of glucose transfer in human erythrocytes by phenolphthalein, phloretin and stilboestrol.

1. Phenolphthalein, like other diphenols, has been shown to be a competitive inhibitor of the facilitated transfer system for glucose in the human erythrocyte.2. The concentration producing 50% inhibition is lower at low temperatures and increases steadily over the temperature range 10-40 degrees C. An Arrhenius plot of the results gives a slope of 19,300 cal/mole.3. The effect of temperature on inhibition by phloretin and stilboestrol has also been studied. The temperature variation of the concentration of phloretin giving 50% inhibition is similar to that for phenolphthalein, but that for stilboestrol is much less.4. There is a high cell/medium distribution ratio for stilboestrol, and the possibility that this may affect the temperature dependence of the aqueous concentrations required to give 50% inhibition is discussed.