Presence of ubiquitin in bovine post-mortem cardiac muscle

We prepared sarcoplasmic proteins from bovine cardiac muscle immediately after slaughter (1.0 h; 0 days) and from stored muscle at 1, 2 and 7 days post-mortem for SDS-PAGE and Western blotting analysis. Characterization of the ubiquitin antiserum (Sigma, St Louis) showed clear and strong recognition of the ubiquitin band (8.6 kDa) and another minor band (17 kDa) in the purified ubiquitin sample (Sigma, St Louis). Among the sarcoplasmic proteins prepared from stored muscle at 0 and 7 days, this antiserum also reacted with bands corresponding to purified ubiquitin and small amounts of some other, higher-molecular-mass proteins (about 25 and 30 kDa) which were considered to be ubiquitin–protein conjugates. However, the 25 kDa band was faint in the 7 days sample, suggesting that it had degraded. We compared these results with those from our previous study of bovine skeletal muscles, in which both ubiquitin and the ubiquitin-protein conjugates had almost disappeared in the samples tested at 10 days post-mortem.