M-line protein: Presence of two non-equivalent high molecular weight components

M-line enriched protein preparations were prepared from glycerated rabbit muscle myofibrils by means of three alternate procedures and analysed with SDS-polyacrylamide gel electrophoresis. A doublet corresponding to polypeptides with molecular weights of 193,000 and 182,000 was obtained in a ratio of2:3, respectively. The two bands are evident in SDS-gels of purified myofibrils, indicating that the proteins represent intrinsic M-line structural peptides. Transmission electron micrographs of the extracted myofibrils confirmed the effectiveness of the extraction procedures for removing M-line proteins. The possible significance of the M-line proteins to meat science is discussed.