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

Thrombin/antithrombin III (AT-III) proteolytic system is well known for its function in blood coagulation. Thrombin is expressed in skeletal muscle but nothing is known about the presence of AT-III in the tissue. In postmortem muscle this system has been and is still totally ignored. We therefore successfully attempted to purify AT-III from bovine skeletal muscle and characterized the purified protein (identified as AT-III by N-ter sequencing and mass spectrometry finger print) for its physicochemical and inhibitory properties. As the human blood serpin, muscle AT-III is thermolabile and stable only at alkaline pH (pH 9–10). The muscle serpin inhibits strongly thrombin in a heparin dependent manner and trypsin. Phosphatidylserine (PS) externalization demonstrated in the present work suggested that prothrombin can be activated to thrombin through binding of the activator complex on the external PS groups. PS externalization is concomitant with shrinkage of muscle fibers indicating that muscle cells are engaged in the cell death program known as apoptosis few minutes after death. We then discussed the potential role of this proteolytic system in postmortem apoptosis development as well as in the control of low voltage electrical stimulation efficiency.