Purification and partial characterization of antithrombin III from bovine skeletal muscle and possible role of thrombin in postmortem apoptosis development and in efficiency of low voltage electrical stimulation

Serine Protease Inhibitors as Good Predictors of Meat Tenderness: Which Are They and What Are Their Functions?

Since years, serine proteases and their inhibitors were an enigma to meat scientists. They were indeed considered to be extracellular and to play no role in postmortem muscle proteolysis. In the 1990's, we observed that protease inhibitors levels in muscles are a better predictor of meat tenderness than their target enzymes. From a practical point of view, we therefore choose to look for serine protease inhibitors rather than their target enzymes, i.e. serine proteases and the purpose of this report was to overview the findings obtained. Fractionation of a muscle crude extract by gel filtration revealed three major trypsin inhibitory fractions designed as F1 (Mr:50-70 kDa), F2 (Mr:40-60 kDa) and F3 (Mr:10-15kD) which were analyzed separately. Besides antithrombin III, an heparin dependent thrombin inhibitor, F1 and F2 comprised a large set of closely related trypsin inhibitors encoded by at least 8 genes bovSERPINA3-1 to A3-8 and able to inhibit also strongly initiator and effector caspases. They all belong to the serpin superfamily, known to form covalent complexes with their target enzymes, were located within muscle cells and found in all tissues and fluids examined irrespective of the animal species. Potential biological functions in living and postmortem muscle were proposed for all of them. In contrast to F1 and F2 which have been more extensively investigated only preliminary findings were provided for F3. Taken together, these results tend to ascertain the onset of apoptosis in postmortem muscle. However, the exact mechanisms driving the cell towards apoptosis and how apoptosis, an energy dependent process, can be completed postmortem remain still unclear.

Caspases and Thrombin Activity Regulation by Specific Serpin Inhibitors in Bovine Skeletal Muscle

In living cells, after activation, protein inhibitors constitute the last step of proteases activity regulation. This review intends to provide original information about a group of bovine muscle serine proteases inhibitors belonging to the Serpin superfamily and characterized at the gene and protein level. This report is the only one and the first to provide much information on this group of proteases inhibitors of the serpin type and their potential biological functions. Amongst the eight genes identified in bovine, three serpins were purified from the muscle tissue and characterized. These are two members of the bovSERPINA3 family, i.e., bovSERPINA3-1 and A3-3, and the last one is antithrombin III (AT-III or BovSERPINC1). BovSERPINA3 family comprises at least eight protein members encoded by different genes mapped on chromosome 7q23-q26 cluster. BovSERPINA3-1 and A3-3 were shown to locate within muscle cells and are cross-class inhibitors strongly active against trypsin as well as against human initiator and effector caspases 8 and 3. They constitute a key apoptosis control in mammals. They were thus expressed in proliferating and confluent myoblasts phases where cells must be alive but not in myotubes. Antithrombin III inhibits trypsin and, in a heparin dependent manner, thrombin. AT-III and its mRNA were expressed in muscle cells and in differentiating primary myoblasts in culture.

In vitro proteolysis of myofibrillar proteins from beef skeletal muscle by caspase-3 and caspase-6

The objective of the study was to investigate in vitro degradation of myofibrils by caspase-3 or -6. Myofibrillar proteins prepared from beef skeletal muscle were incubated with caspase-3 or -6 at 30 °C for 2 or 12 h, and subsequently, protein degradation was detected. Results showed that caspase-3 and -6 reproduced the degradation patterns of titin and nebulin observed during normal postmortem (PM) aging; however, they only reproduced the 28 kDa fragment derived from troponin-T. Caspase-3 induced only minor degradation of desmin. However, caspase-6 caused increasing degradation of desmin with extended incubation time and produced three degradation fragments (45, 29, and 27 kDa) of which only the 45 kDa fragment has been reported in aged beef. Therefore, caspase-3 or -6 could only reproduce a part of myofibrillar protein degradation or degradation fragments observed in naturally aged meat and may be involved in PM proteolysis of muscle proteins together with other endogenous proteases.