The Role Of Ubiquitin-Proteasome In Mutton Ageing

Tenderness is of importance to meat quality,which is affected by rigor and ageing at post mortem.The primary reason of tenderization is both the degradation of myofibrillar proteins and cytoskeletal proteins,as well as the destruction of muscular ultrastructure.Enzymes which may play role in tenderization are various,including calpain,cathepsin,caspase and proteasome.Ubiquitination is one kind of post-translational modification of proteins whose main function is guiding proteins to proteasome in body.However,the role of ubiquitin-proteasome pathway at post mortem is unknown.One sheep muscle longissimus lumborum(LL)was used for different treatments,including control,ubiquitination inhibited and proteasome inhibited.The sample of myofibrils was collected at 6,15,24 and 48 h after slaughter.Ultrastructure was determined by transmission electron microscope while sarcomere length was analyzed.Results showed that,the sarcomere length of ubiquitination inhibited samples was the shortest than others(P<0.05)at each time while ultrastructure of proteasome inhibited samples was destructed slighter.Meat samples were collected at 6,15,24 and 48 h after slaughter,from same groups mentioned above.Myofibrillar proteins were analyzed by SDS-PAGE and LC-MS.Relative activities of Calpain were detenmined by casein zymography.Results showed that,distinct band were determined containing actin and myosin.The volumes,both of actin and myosin,in proteasome inhibited samples were higher than control(P<0.05).The activites of proteasome,including peptidyl glutamyl peptide hydrolase,Chymotrypsin-like and trypin-like,in nine sheep,which had similar calpain activites and initial level of ubiquitination in myofibrillar proteins,were determined at 0.5 h,12 h,24 h and 48 h postmortem.Shear force and myofibrillar fragmentation index were determined at 24 h and 48 h postmortem.The correlation between proteasome activites and shear force/MFI were analyzed.Results showed that,the Chymotrypsin-like and peptidyl glutamyl peptide hydrolase activites was the highest at 24 h(P<0.05).ChT-L and PGPH activities at 48 h,as well as T-L at 24 h,were correlated to the amount of MFI varied from 24 h to 48 h after slaugher(P<0.01)while T-L at 48 h was correlated to the MFI varition(P<0.05).