Fructose metabolism in the human red blood cell

In normal red blood cells, at similar ranges of substrate concentrations, utilization of fructose was, in contrast to that of glucose, dependent on the substrate concentration. This was evident with respect to both the Embden Meyerhof and the phosphogluconate pathways. These differences correlated better with the higher K(m) of hexokinase for fructose than that for glucose. There was a competitive inhibition of fructose utilization when erythrocytes were simultaneously exposed to both sugars. At high concentrations of fructose, the increase in lactate formation lagged behind fructose utilization. Measurement of the concentration of glycolytic intermediates indicated some accumulation of pyruvate but not in an amount sufficient to account for the deficient lactate formation. On the basis of these results, it is conceivable that, due to the preponderance of glucose in vivo and the lower K(m) of hexokinase for this sugar, fructose is not a major energy substrate in human erythrocytes even though it can be substantially utilized by them.