Skeletal Muscle Proteases and Protein Turnover

Abstract

Schoenheimer and Rittenberg’s paper published nearly 50 years ago (Schoen-heimer and Rittenberg, 1940) established that accumulation of muscle tissue or muscle growth must depend on both the rate of muscle protein synthesis and the rate of muscle protein degradation. Despite this axiom, most of the attention of animal scientists during the period from 1940 to 1980 focused on increasing the rate of muscle growth by increasing the rate of muscle protein synthesis. Because of this, a great deal is known about the mechanism of muscle protein synthesis and how it is controlled. Little is known, however, about the mechanism of muscle protein degradation. It is clear that muscle proteins turn over metabolically with half lives ranging from 2 to 20 days (Low and Goldberg, 1973; Koizumi, 1974; Rubenstein et al., 1976; Martin et al., 1977; Zak et al., 1977; Millward et al., 1978; Martin, 1981; Wolitsky et al., 1984), but the nature of the proteolytic enzymes responsible for this turnover remains unknown. It was learned in 1969 that the rate of muscle protein degradation can vary over a wide range in response to physiological demand (Goldberg, 1969a,b).