IDENTIFICATION OF THE 30-KDA POLYPEPTIDE IN POST-MORTEM SKELETAL-MUSCLE AS A DEGRADATION PRODUCT OF TROPONIN-T

Although a 30 kDa polypeptide frequently is seen by sodium dodecyl sul fate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of post mo rtem (pm) skeletal muscle and in turn is used as an indicator of prote olysis, its origin has not been conclusively identified. We used antib odies to selected myofibrillar proteins, including some known to be de graded pm, to identify this polypeptide. The left side of eight beef c arcasses was electrically stimulated (ES) within 1 h after slaughter, and the right side served as the non-stimulated (NS) control. The long issimus lumborum (LL) muscle was removed from the carcass at 24 h pm a nd was stored at 2 degrees C. Myofibrils were prepared from the LL mus cle immediately after stimulation (0 day) and from the stored muscle s ample at 1, 3, 7, 14 and 28 days pm for analysis of SDS-PAGE and Weste rn blots. By SDS-PAGE, troponin-T (TN-T) decreased in amount more rapi dly pm in ES samples than in NS samples. By SDS-PAGE, a 30 kDa band in creased and became a prominent band by 7 days pm in both NS and ES sam ples. A monoclonal antibody (mAb) to TN-T labeled purified TN-T, as we ll as the TN-T in myofibrils, a promi nent 30 kDa polypeptide and a fa mily of lower molecular mass polypeptides in pm muscle. This mAb also labeled a 30 kDa band that had been electrophoretically purified from pm muscle. The 30 kDa band in blots of myofibrils was prominent from d ay 3 through 28 in bath ES and NS samples, but was exaggerated in the ES samples. Antibodies to other myofibrillar proteins (titin, nebulin, alpha-actinin and desmin) did not label the 30 kDa band. We conclude, on the basis of labeling with a mAb to TN-T, that the prominent 30 kD a polypeptide often observed in pm bovine skeletal muscle is a degrada tion product of TN-T and, furthermore, that an entire family of lower molecular mass polypeptides (one of which is the 30 kDa polypeptide) o riginates from TN-T.