An overview of protein synthesis, degradation and the regulation of protein content in skeletal muscle.

In this review paper various aspects of protein synthesis and breakdown in skeletal muscle will be surveyed as an introduction to the more specialized topics concerned with anabolic agents and the production of muscle protein. The quantitatively important role of skeletal muscle in total protein and amino acid metabolism will be evaluated by considering the size, composition (RNA and protein) and metabolic activity of this tissue in mammalian organism. This will provide an initial basis for understanding how internal and external environmental factors may affect the rate of growth and final size of the muscle mass in the intact organism. The steps in protein synthesis, involving aminoacid activation, initiation, peptide chain elongation and termination will be described, with particular reference to the synthesis of protein in fibers of skeletal muscle. This account will include a review of the specificity of myofibrillar protein synthesis and the relationships between the biochemical aspects of protein synthesis and the structural organization of the muscle cell. The role of messenger RNA, tRNA and soluble protein factors in the regulation of muscle protein synthesis in the growing animal will be reviewed, together with a short account of the ways in which hormones may modulate the rate of protein synthesis in muscle cells. However, the available data do not lead to definite conclusions concerning the rate limiting step(s) in muscle protein synthesis or the quantitative significance of factors which affect them. The mechanisms and regulation of protein degradation and the role of degradation in the regulation of muscle protein content will also be discussed.