The phosphoproteins of the sickle erythrocyte membrane.

The uptake of 32P from exogenous 32Pi into membrane proteins of sickle erythrocytes has been analyzed. The phosphorylation of spectrin is normal in sickle cells. There is, however, a substantial increase in 32P in the sialoproteins of the membrane, which can be demonstrated after fractionation or selective proteolysis. Normal and sickle erythrocytes were separated on Stractan gradients and average cell age was determined using the remaining pyruvate kinase activity as a marker. The altered phosphorylation of sickle cells was not seen in young normal cells, suggesting that it was not related to cell age. The altered phosphorylation was also not correlated with the level of reticulocytes in these fractions. This result is further evidence for abnormalities in the sialoproteins of sickle erythrocytes and is the first demonstration of altered sialoprotein phosphorylation in the red cell.