Tenderness is governed by postmortem biochemical processes, particularly proteolysis. In mammals, the calpain system is generally accepted as the main system involved in postmortem proteolysis. In poultry, the 2 calpains (mu and mu/m--a form only found in bird tissue) have greater calcium sensitivity. In this study, we quantified by zymography the changes in postmortem calpain system activity. The mu/m-calpain activity remained steady, whereas the mu-calpain activity had disappeared by 6 h after postmortem, showing an activation by calcium. Changes in the electrophoretic pattern of sarcoplasmic and myofibrillar proteins are observed in the first postmortem hours concomitantly to the decrease in mu-calpain activity. The 30-kDa protein, considered as a good marker of postmortem aging in cattle, appeared from 6 h and then steadily increased. In chicken muscle, the rapid maximum tenderness reached could be explained by a greater activation of the calpain system.

No abstract

Because genetic defects relating to the ubiquitin-proteasome system were reported in familial parkinsonism, we evaluated proteasomal function in autopsied brains with sporadic Parkinson's disease. We found that proteasome peptidase activities in a fraction specific to the proteasome were preserved in five brain areas (including the striatum) of Parkinson's disease where neuronal loss is not observed. Striatal protein levels of two proteasome subunits were normal in Parkinson's disease but reduced mildly in disease controls (multiple system atrophy). Our brain data suggest that a systemic, global disturbance in the catalytic activity and degradation ability of the proteasome itself is unlikely to explain the cause of Parkinson's disease.

The metabolic characteristics of 12 skeletal muscles of the sheep were studied. Glycolytic activities (hexokinase, glycogen synthetase I and D, phosphorylase a and b, phosphofructokinase) were measured. Myofibrillar ATPase activity was evaluated. Oxygen consumption, respiratory control and carnitine palmityl transferase, isocitrate dehydrogenase, succinate dehydrogenase and cytochrome oxidase activities were measured in isolated mitochondria. Three metabolic types could be distinguished; (1) essentially oxidative slow twitch muscles, typified by the supraspinatus and infraspinatus, having low ATPase activity, (2) fast twitch red muscles, typified by the longissimus dorsi and the semimembranosus, having a higher ATPase activity and both high oxidative and high glycolytic activity, and (3) essentially glycolytic fast twitch muscles, typified by the tensor fascia lata and the semitendinosus, having the highest ATPase activity.

The physiologic function of proteasome remains unclear. Evidence suggests a role in degradation of ubiquitin-protein conjugates, MHC antigen presentation, and some specificity of substrate within certain cell types. To explore further the properties of proteasome we have examined its effect on a well defined structure, the myofibril. We find that despite its large size (20S) proteasome is able to degrade myofibrils and intact, permeabilized muscle fibrils. The proteins degraded showed some specificity because actin, myosin and desmin were degraded faster than alpha-actinin, troponin T and tropomyosin. Changes in ultrastructure were slow and included a general loss of structure with Z and I bands effected before the M band and costameres.

No abstract

We have identified and characterized a specific nuclease activity to be tightly associated with proteasomes. Using tobacco mosaic virus RNA (TMV-RNA) as substrate to analyze and quantify the cleavage reaction, we supply several lines of evidence that this nuclease activity is an integral part of proteasomes. Thus, RNase activity was coincident with the elution profiles of proteasomes at each stage of purification. Proteasomal nuclease activity was resistant to strong dissociation conditions using 480 mM KC1, 0.5% sodium lauroylsarcosinate, and 6 M urea. This nuclease activity remained associated with an urea-resistant subcomplex of the proteasome comprising a specific set of proteins. Finally the digestion of TMV-RNA led to a well defined pattern of RNA fragments while 5 S ribosomal RNA and globin mRNA were not degraded. These results provide further evidence that proteasomes are able to discriminate between different RNAs, and the possible involvement of proteasomes in translation control is discussed.

During aging, the production of free radicals increases. This can result in damage to protein, the accumulation of which is characteristic of the aging process. This questions the efficacy of proteolytic systems. Among these systems, the proteasome and the adenosine triphosphate-ubiquitin-dependent pathway have been shown to play an important role in the elimination of abnormal proteins. There are two major steps in the ubiquitin-proteasome pathway: the conjugation of a polyubiquitin degradation signal to the substrate and the subsequent degradation of the tagged protein by the 26S proteasome. The 26S proteasome is build-up from the 20S proteasome, which is a cylinder-shaped multimeric complex, and two additional 19S complexes. The 20S proteasome can also bind to 11S regulator and is then implicated in antigen presentation. These regulators confer a high adaptability on proteasome. With advancing age, predisposition to neurodegenerative diseases increases. These diseases are also characterized by protein aggregation. Several findings such as the presence of ubiquinated proteins, usually broken down by proteasomes, and genetic anomalies involving the ubiquitin-proteasome system (parkin, UCH-L1) suggest a link between the ubiquitin-proteasome pathway and the genesis of these diseases.