The synthesis of myofibrillar and soluble proteins in cell-free systems and in intact cultured muscle cells from newborn polymyopathic hamsters

Abstract

Myofibrillar proteins from both hearts and skeletal muscles of control and myopathic hamsters, at different ages, were extracted and analysed electrophoretically. Significant quantitative differences were found, more or less uniformly affecting all the myofibrillar components, even of embryonic hearts. In an attempt to determine whether the observed differences become established as the result of defective biosynthesis or for some other reason, reconstituted cell-free systems were used to study the in vitro synthesis of some of the specific myofibrillar protein components. A generally defective biosynthesis of myosin, (both heavy and light chains) and actin was demonstrated, while gel-electrophoretic analysis of soluble proteins synthesized in vitro showed that the profile of radioactivity in systems derived from myopathic animals was also generally lower than in those from controls. In order to demonstrate that the defect in protein synthesis was present in intact beating heart cells, myopathic and control heart cells were treated with radioactive amino acids, and the soluble and myofibrillar proteins subsequently extracted and fractionated. The biosyntheses of both types of proteins were clearly impaired in the case of cells derived from myopathic animals.