High‐resolution two‐dimensional electrophoresis of myofibrillar proteins with immobilized pH gradients

Previous studies by chromatography and electrophoresis have demonstrated that myosin is composed of two classes of polypeptide chains: high relative molecular mass (Mr) components (200 000) and a class of lower Mr species, called the “light chains” (LC). It has been shown before by others that the slow‐twitching fibers contain 2 types of isoforms: LC1s and LC2s, while the fast‐twitching fibers contain 3 types: LC1f, LC3f and LC2f, the latter also existing as phosphorylated forms. In the present investigation, utilizing two‐dimensional (2‐D) maps generated with narrow immobilized pH gradients in the first dimension, a higher resolution of the myosin LC has been achieved. The LC1s chains are further fractionated into at least four isoforms; LC2s into three; LC2f into four and LC3f into three sub‐species in rabbit muscles. Skeletal muscle tropomyosin, which is separated into three forms (αs, αf and β), is here resolved into six components, while actin from skeletal muscle, previously described mainly as a single chain (α), is here sub‐fracionated into four isoforms of identical Mr and different charge. The series of isoforms here reported could represent a fine probe for investigating such complex phenomena as the cellular differentiation of human satellite cells from normal and pathological subjects in greater detail than before.