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Title: Sarcomeric thick and thin filament overlap influences postmortem proteolysis

item Bowker, Brian

Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 1/29/2007
Publication Date: 3/19/2007
Citation: Weaver, A.D., Jouault, L., Bowker, B.C., Grant, A.L., Gerrard, D.E. 2007. Sarcomeric thick and thin filament overlap influences postmortem proteolysis [abstract]. Midwestern Section of the American Society of Animal Science Proceedings. Paper No. 120.

Interpretive Summary:

Technical Abstract: The interaction between sarcomere length (SL) and proteolysis on meat tenderness is not clear. Indeed, the extent of thick and thin filament overlap alters actomyosin binding and may alter substrate availability during aging. The objective of this study was to determine the influence of sarcomere length on proteolytic degradation in beef. In one study, beef carcasses were subjected to either hip (HS) or normal suspension (NS). At 24 h, longissimus dorsi (LD), semitendinosus (ST), and psoas major (PM) muscles were removed and aged for 2, 4, 7 or 10 d. In a second study, ST muscles were removed from carcasses and dissected into strips parallel to fiber orientation. Strips were either stretched 40 percent and restrained or placed in an ice bath. After rigor completion, strips were divided into 2.5 cm cross sections and randomly assigned to 2, 4, 7 or 10 d aging treatments. Myofibrils were isolated and sarcomere length was determined. Additional samples were frozen for shear force analysis. Muscle proteins were extracted and subjected to SDS-PAGE and western blot analyses to determine troponin T (TnT) proteolysis. HS increased sarcomere length in the LD and ST samples and shortened sarcomeres in PM samples. Analysis of the four TnT-specific immunoreactive bands confirmed degradation increases with aging. An increase in the relative intensity of bands two, three and four confirmed TnT degradation; however, sarcomere length had no effect on the rate or extent of proteolysis in the LD and ST. Lack of significance was likely due to the small range in sarcomere lengths achieved using HS. Actomyosin bonds in the overlap region would not necessarily differ over the SL ranges generated. However, SL in PM samples was sufficient to alter the amount of actomyosin bonds. Disappearance of band one and a corresponding appearance of bands three and four was less evident between 4 and 7 d in normally suspended PM samples suggesting proteolysis may be hindered in muscles possessing long (~3.7 um) SL. Western blot analysis indicated the appearance of bands three and four was greater in the 40 percent-stretched samples suggesting degradation of TnT is sarcomere length-dependent.