Intermuscular variation in tenderness: Association with the ubiquitous andmuscle-specific calpains

The biochemistry of intermuscular variation in tenderness is not fully unde rstood. To investigate the role of the calpains in this process we performe d two experiments using bovine and ovine species. In the bovine experiment, two distinct muscles, longissimus thoracis et lumborum (LT) and psoas majo r (PM), were used. In the ovine experiment, four muscles, LT, PM, semimembr anosus (SM), and semitendinosus (ST), were used. Muscles were sampled at de ath for the determination of the steady-state mRNA level of calpains and ca lpastatin and the activities of calpain 1, 2, and calpastatin. Muscles were also sampled to determine the temporal changes in pH, tenderness, and the activity of the ubiquitous calpain system during postmortem aging. The resu lts of the relative rate of tenderization in both species was found to be r elated to muscle type; LT had the highest value in both species. Within spe cies, the mRNA steady-state levels of calpain 1 and calpastatin were simila r in various bovine and ovine muscles. Bovine calpain 2 mRNA level was sign ificantly lower in the LT than in the PM. Ovine calpain 2 mRNA level was lo wer, but not significantly different, in the LT compared to the other muscl es. The mRNA level of bovine calpain 3 was significantly higher in the LT m uscle than in the PM. In the ovine, the mRNA level of calpain 3 was highest in the LT, followed by SM, PM, and ST. Results on the activity of the ubiq uitous calpain system in various muscles at death were dependent on muscle type and species. Temporal changes in the activity of calpains and calpasta tin during the first 24 h of postmortem aging were similar in the muscles s tudied: calpain 1 and calpastatin declined significantly and calpain 2 rema ined relatively unchanged. The temporal changes in muscle pH in both experi ments indicated that the extent and rate of pH decline during aging was rel ated to muscle type. Correlation analysis between the relative rate of tend erization and mRNA expression of calpains revealed a strong relationship wi th calpain 3 in both species.