Dynamic aspects of structural proteins in vertebrate skeletal muscle.

In this review, our current knowledge on the structural proteins of vertebrate skeletal muscle is briefly outlined. Structural proteins include the contractile proteins (actin and myosin), the major regulatory proteins (troponin and tropomyosin), the minor regulatory proteins (M-protein, C-protein, F-protein, I-protein, and actinins), and the scaffold proteins (connectin, desmin, and Z-protein). In addition, the relative turnover rates of the muscle proteins (M-protein greater than or equal to troponin greater than soluble protein as a whole greater than tropomyosin not equal to alpha-actinin greater than myosin greater than 10S-actinin greater than actin) are discussed. The changes in the turnover of muscle proteins are compared in denervated and dystrophic muscles. The properties of the various proteases in muscle, including alkaline protease, calcium-activated neutral protease (CANP), and acidic protease (cathepsins), and the structural alterations of myofibrils by these proteases are also described. Finally, the role of proteases and their inhibitors in diseased muscle is summarized, with focus on CANP and its inhibitors, leupeptin and E-64.