Ractopamine-induced remodeling in the mitochondrial proteome of postmortem longissimus lumborum muscle from feedlot steers

Dietary ractopamine causes a muscle fiber shift in cattle, and the biochemistry of mitochondria in postmortem muscles is influenced by fiber type. Nonetheless, the influence of ractopamine on beef skeletal muscle mitochondrial proteome has not been evaluated. Therefore, the objective of this study was to examine the effects of dietary ractopamine on mitochondrial proteome of postmortem longissimus lumborum (LL) from feedlot crossbred steers. Pen-housed crossbred steers were fed either a corn-based basal diet (CON) or a diet top-dressed with Optaflexx 45 (Elanco Animal Health) to provide 400 mg of ractopamine hydrochloride/steer per day (RAC). Ractopamine was fed the last 28 days prior to the harvest. The LL muscle samples were obtained from nine (n = 9) RAC and nine (n = 9) CON carcasses. The mitochondrial proteome was analyzed using two-dimensional gel electrophoresis and mass spectrometry. Seven differentially abundant proteins (P < 0.05) were identified. Three proteins over-abundant in RAC were complement component 1 Q subcomponent-binding protein (C1QBP), very long-chain specific acyl-CoA dehydrogenase (ACADVL), and aconitate hydratase (ACO2). On the other hand, four proteins, ATP synthase subunit beta (ATP5B), prohibitin (PHB), cytochrome b-c1 complex subunit (UQCRC1), and thioredoxin-dependent peroxide reductase (PRDX3), were over-abundant in CON. The differentially abundant proteins belong to four functional groups – energy metabolism (ATP5B, UQCRC1, and ACO2); chaperone activity (C1QBP and PHB); redox metabolism (PRDX3); and fatty acid degradation (ACADVL). The increased protein synthesis and leanness reported in ractopamine-fed cattle may be attributed to the increased expression of enzyme involved in fatty acid degradation and the decreased expression of enzymes involved in oxidative phosphorylation. Additionally, the decreased tenderness previously reported in beef from ractopamine-fed cattle may be attributed to the increased expression of antiapoptotic protein (C1QBP) and decreased expression of proapoptotic protein (PHB) resulted from ractopamine supplement.