Effect of proteasome inhibitor on sarcoplasmic protein of bovine skeletal muscle during storage

Bovine skeletal muscle, immediately after slaughter (1.5 h; 0 d), was buffered, homogenized treated with proteasome inhibitor, and stored (2 d) for SDS-PAGE and Western blotting analysis. Ubiquitin antiserum (Sigma, St Louis) reacted with bands corresponding to purified ubiquitin and small amounts of other higher-molecular-mass proteins (about 30 and 40 kDa) which were considered to be ubiquitin-protein conjugates. These bands were faint in the control 2 d sample, suggesting that they had degraded. However, these tendencies of the ubiquitin positive bands to decrease were not clearly observed in the sample treated with proteasome inhibitors (MG132 and Lactacystin). These results suggest that both ubiquitin and the ubiquitin-protein conjugates were present in the skeletal muscle immediately after slaughter and they were then degraded during storage. This degradation was partially due to the action of proteasome.