Identification of abnormally [32P]-phosphorylated cyanogen bromide cleavage product of erythrocyte membrane spectrin in Duchenne muscular dystrophy.

We measured [32P]-phosphorylation of erythrocyte membrane spectrin band 2 peptides from patients with Duchenne muscular dystrophy. Erythrocyte ghosts were prepared and subjected to [32P]-phosphorylation by endogenous protein kinase incubations. Purified spectrin was then cleaved by cyanogen bromide, and the resulting peptides were analyzed by electrophoresis on 5%/15% SDS polyacrylamide stacking slab and tube gel systems. More than 50% of the incorporated [32P] was associated with a single band, CN-A, with an apparent molecular weight of 23 kilodaltons. The Coomassie blue-stained peptides were identical in patients and controls. Band CN-A represented approximately 2% of the total peptide protein but was more [32P]-phosphorylated in patients than in controls.