Identification and quantification of myosin heavy chain isoforms in bovine and porcine longissimus muscles by LC-MS/MS analysis.

To identify and quantify the myosin heavy chain (MHC) isoforms in porcine and bovine longissimus thoracis (LT) muscles, LC-MS/MS and label-free quantification were conducted. 2a, 2x, 2b and slow isoforms were identified in porcine LT muscle, whereas bovine LT muscle contained 2a, 2x and slow isoforms. The highest peak intensity (44.32%) of MHC 2b was observed in porcine LT muscle, whereas the peak intensity of MHC 2a was the highest (71.15%) in bovine LT muscle (p<0.05). MHC-based fiber compositions for porcine and bovine LT were also the highest in types IIB (61.13%) and IIA (61.90%), respectively (p<0.05). Spectral count and peak intensity had positive correlations with MHC-based fiber composition (p<0.01), however the spectral count and peak intensity of total peptides were not acceptable for MHC quantification because of the limited reliability of the protein and common peptide, respectively. Therefore, the peak intensity of unique peptides would be the most acceptable trait for MHC quantification.