S100a sub(o)( alpha alpha ) protein, a calcium-binding protein, is localized in the slow-twitch muscle fiber

To elucidate cellular and ultrastructural localizations of the alpha subunit of S100 protein (S100- alpha ) in skeletal muscle, the authors used immunohistochemical and enzyme immunoassay methods. The immunnhistochemical study revealed that S100- alpha is mainly localized in slow-twitch muscle fibers. At the ultrastructural level, S100- alpha is associated with polysomes, sarcoplasmic reticulum, the plasma membrane, the pellicle around lipid droplets, the outer membrane of mitochondria, and thin and thick filaments, by immunoelectron microscopy.