A sensitive SDS-PAGE method separating myosin heavy chain isoforms of rat skeletal muscles reveals the heterogeneous nature of the embryonic myosin.

Myosin isoforms are used as markers of heterogeneity and plasticity of skeletal muscle fibers and motor units. Tedious and time-consuming methods, needing microgram or milligram amounts of myosin are widely used to characterize the heavy subunits. We here describe a sensitive method that separates in nanogram or microgram amounts the heavy chains of immature, fast and slow adult rat muscles in complex mixtures of myosins. Though the method is assembled from published procedures (SDS-PAGE, peptide mapping in the presence of SDS, silver stain) for the logical extensions introduced the end-product is a powerful tool to separate and characterize these high molecular weight biopolymers until now inseparable from complex mixtures. The method reveals the heterogeneous nature of the embryonic myosin heavy chains.