Increased [ 32 P]‐phosphorylation of tryptic peptides of erythrocyte spectrin in duchenne muscular dystrophy

Increased [ 32 P]‐incorporation in tryptic peptides of the erythrocyte membrane protein spectrin Band 2 in Duchenne muscular dystrophy (DMD) was studied in a consecutive series of 10 matched DMD/control pairs. Spectrin was [ 32 P]‐phosphorylated by cyclic AMP‐independent endogenous membrane protein kinase in the presence of [γ‐ 32 P]ATP. [ 32 P]‐labeled spectrin was isolated, purified, and subjected to tryptic cleavage with excess trypsin. The resulting peptides were separated on a high‐resolution 5%/15% stacking SDS‐polyacrylamide gel electrophoresis system. Liquid scintillation counting was performed on sequential slices of unstained gels. A broad [ 32 P]‐labeled band containing a number of [ 32 P]‐polypeptides was found to be more highly [ 32 P]‐phosphorylated in DMD patients than in their matched controls. This band migrated with an apparent molecular mass of 4.8–5.2 kilodaltons and contained approximately 55% of total [ 32 P] radioactivity covalently bound to spectrin peptides. These data demonstrated an increased [ 32 P]‐phosphorylation of an identifiable tryptic peptide fraction in DMD that is consistent with previous reports of increased spectrin Band 2 [ 32 P]‐phosphrylation in DMD.