The overall objective of the work in this dissertation was to characterize -calpain, m-calpain, and calpastatin activities in order to learn more about the system in the live animal as well as its potential effects on postmortem proteolysis. Animal models of efficiency and growth were used to achieve this objective.

The first specific objective was to evaluate muscle protein turnover differences in pigs selected for residual feed intake (RFI). Muscle samples were collected, and insulin signaling, protein synthesis, and specific protein degradation proteins were analyzed for expression and activities in twelve gilts each from low (LRFI) and high (HRFI) RFI lines. LRFI (more efficient) pig muscle had greater calpastatin activity and a lower -calpain:calpastatin activity ratio compared to HRFI counterparts (P<0.05). LRFI pig muscle had less 20S proteasome activity (P<0.05). No differences in protein synthesis pathways were observed (P>0.05). Postmortem proteolysis was determined in the longissimus from generation 8 of the LRFI versus HRFI pigs (n=9). Less μ-calpain autolysis and troponin-T degradation were observed at 3 d postmortem in LRFI pigs (P<0.05), indicating slowed postmortem proteolysis during postmortem aging. These data provide significant evidence that less protein degradation occurs in the more efficient LRFI pigs, which may account for a significant portion of their increased efficiency.

The second specific objective was to determine calpain system activity and postmortem proteolysis in three muscles from growing and mature beef cattle (n=6 each). The -calpain:total calpastatin activity ratio was lesser in mature animals (P=0.08), suggesting less proteolytic potential compared to the younger animals. Muscles from the mature group had greater calpastatin activity compared to calves at 6 days postmortem and had less -calpain autolysis and protein degradation over time (P<0.01). These data suggest that calpastatin activity in muscle from older animals is more persistent postmortem, partially explaining tougher meat from older animals, even after aging.

The third specific objective was to characterize two calpastatin activity peaks (Calpastatin I and Calpastatin II) detected during anion exchange chromatography. While there is less total activity in the Calpastatin I peak, both calpastatins inhibit - and m-calpain similarly. 2D immunoblotting for calpastatin detected anti-calpastatin immunoreactive proteins migrating at 145 and at 60 kDa in both Calpastatin I and Calpastatin II eluate samples. The 145 kDa spots were also identified as calpastatin via mass spectrometry. 2D gels were stained to detect phosphoprotein and total protein abundance. Calpastatin in the Calpastatin II peak stained more intensely with the phosphoprotein stain. We propose that Calpastatin II is more phosphorylated, resulting in its later elution from an anion exchange column. Phosphorylation may be a mechanism to regulate calpastatin inhibitory activity.

This work further elucidates the role that the calpain system plays in muscle growth and development, providing a greater understanding of muscle biology, efficiency, and meat quality.