Anomeric preference of glucose utilization in rat erythrocytes

The beta-anomer of glucose relative to the alpha-anomer was more rapidly metabolized into lactate by rat erythrocytes at 37 degrees C (beta/alpha ratio = ca. 1.3): the amounts of alpha- and beta-D-glucose metabolized into lactate during 3 min were 0.21 and 0.27 mumol/gHb, respectively. Also, the transport of beta-D-glucose into erythrocytes was more rapid than that of alpha-D-glucose: the amounts of alpha- and beta-D-glucose transported into erythrocytes during 3 min were approximately 3.5 and 5.0 mumol/gHb, respectively. Glucose phosphorylation by rat erythrocyte hexokinase (i.e., a possible rate-limiting step in glycolysis) occurred at higher velocities with the beta-anomer than with the alpha-anomer (beta/alpha ratio = 1.28). The Km value of hexokinase for either anomer of glucose was 53 microM. The glucose concentrations in erythrocytes incubated with alpha- and beta-D-glucose reached about 1 mM in 1 min, indicating that hexokinase is almost completely saturated with glucose within less than 1 min. The results suggest that glucose phosphorylation and glucose transport are major and minor determinants, respectively, for the anomeric preference of glucose utilization in rat erythrocytes.