Increased red cell glutamine availability in sickle cell anemia: demonstration of increased active transport, affinity, and increased glutamate level in intact red cells.

Sickle red blood cells (RBCs) have been shown to have an increase in total nicotinamide adenine dinucleotide (NAD) content by an as-yet-unknown mechanism. Because glutamine is an essential precursor in NAD biosynthesis, we have examined the rates of active RBC glutamine transport and glutamine transport kinetics with Michaelis-Menten constant (K[m]) and maximum velocity (V[max]) in RBCs from patients with sickle cell disease, patients with high reticulocyte counts, and normal volunteers. In addition, plasma and RBC levels of glutamine and glutamate in the three groups were analyzed. The rate of active glutamate transport in sickle RBCs increased threefold over that in high-reticulocyte RBCs and increased 15-fold over that in normal RBCs. Glutamine transport K(m) in sickle RBCs was decreased fivefold in comparison with that in the high-reticulocyte group and that in normal control subjects. Glutamine transport V(max) for sickle RBCs was twofold and eightfold higher in comparison with those in the high-reticulocyte RBCs and normal control RBCs, respectively. Finally, the level of RBC glutamate (a byproduct of glutamine in NAD synthesis) in the sickle group was significantly increased in comparison with that in the high-reticulocyte group, whereas the RBC glutamine level was not. The higher glutamate level in sickle cells may suggest a higher glutamine turnover in these cells. These data suggest that sickle RBCs have an increased glutamine availability and affinity that may facilitate the increase in total NAD in sickle RBCs.