Abstract
The effect of leupeptin on turnover of the soluble protein fraction, the myofibrillar protein fraction, and myosin heavy chain was evaluated in muscle cell cultures. Cultures were prepared from the breast muscle of 12-day normal (white leghorn) and dystrophic (line 307) chick embryos. After 7 days in culture, cells were labeled for 16 hr with 1 μCi/ml of [ 3H]Leu and then “chased” for an additional 24 hr in culture medium containing no [ 3H]Leu and 0–75 μg/ml leupeptin. Cultures were analyzed for radioactivity in the soluble protein fraction, the myofibrillar protein fraction, and myosin heavy chain. Leupeptin (75 μg/ml) virtually eliminated loss of radioactivity from the soluble protein fraction, but only minimally affected loss of radioactivity from the myofibrillar fraction or myosin heavy chain. Normal and dystrophic muscle cells responded identically to leipeptin treatment. Thus, the muscle proteases that are specifically inhibited by leupeptin seem to have no major role in initiating myofibrillar protein turnover.
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