Increased turnover of proteins from the sarcoplasmic reticulum of dystrophic chicken muscle cells in tissue culture.

Chicken myoblasts were cultured from the pectoralis muscles of dystrophic and normal 11-day-old embryos. Cells were allowed to grow to fusion (differentiation) and exposed to [35S]methionine for a short period. Subsequently, the decay of labeled proteins in the presence of cycloheximide was measured for various cellular fractions as well as individual proteins isolated from the sarcoplasmic reticulum and separated by gel electrophoresis. Some dystrophic material showed an increased decay when compared to normal material. The most significant (p less than 0.005) difference was found in a Mr = 65,000 component of the sarcoplasmic reticulum. This same component accumulates label at an accelerated rate in the presence of the protease inhibitor leupeptin. Increased turnover of this protein, possibly calsequestrin, may be a manifestation of the genetic disease.