Comparative studies on myofibrillar proteins in different types of skeletal muscle fibers

Abstract

Comparative studies on myofibrillar proteins from fast-twitch red, fast-twitch white and slow-twitch intermediate fibers of guinea pig skeletal muscle were performed, using soleus, semimembranosus proprius, the red and the white parts of vastus lateralis. The myofibrillar proteins were run in SDS-polyacrylamide gel electrophoresis and were compared between these muscles. The gross ratios of myofibrillar proteins, i.e., myosin, actin, α-actinin and troponin-tropomyosin complex, were equal in all fiber types. However, light chains (LC) of myosin were quite different between slow- and fast-twitch fibers. In fast-twitch fibers (both in fast-twitch red and fast-twitch white fibers), light chains were composed of three components, i.e., LC-1 (Mol wt: 24,000), LC-2 (Mol wt: 18,000) and LC-3 (Mol wt: 15,000), whereas in slow-twitch intermediate fiber LC-1 was composed of two subcomponents (Mol wt: 28,000, 27,000) and the molecular weight of LC-2 was 19,000. The LC-3 was not detected in slow-twitch fiber. These different patterns of light chains of myosin is considered to be related to different actinmyosin interaction between slow- and fast-twitch fibers.