Characterization of the phosphorylated state of protein 4.2 from a patient partially deficient in protein 4.2

These studies compare the protein 4.2 found in a patient with osmotically fragile, spherocytic erythrocytes to the normal protein 4.2. The patient protein 4.2 is present in the erythrocyte ghost membranes as a doublet of 74 and 72 KDa at a concentration less than 1% of normal. The patient protein 4.2 becomes highly phosphorylated in the presence of Zn++ and is phosphorylated, relative to the amount of protein present, to a greater extent than the normal 72 KDa protein 4.2. These studies indicate that both the patient and the normal protein 4.2 usually exists in a highly phosphorylated state. The phosphorylation sites on the patient protein 4.2 appear to be more readily cycled than on the normal protein 4.2. Staphylococcus aureus V8 protease generates similar phosphopeptides in both the normal and patient protein 4.2 except for an extra 11 KDa phosphopeptide generated from the 74 KDa form of the protein.