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

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Abstract
Phenolphthalein, like other diphenols, is a competitive inhibitor of the facilitated transfer system for glucose in the human erythrocyte. The concentration producing 50% inhibition is lower at low temperatures and increases steadily over the temperature range 10-40[degree]C. An Arrhenius plot of the results gives a slope of 19,300 cal/mole. The effect of temperature on inhibition by phloretin and stilboestrol was also 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. 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.