Turnover rates of muscle proteins in cardiac, skeletal, and smooth muscle: turnover rate related to muscle function.

The turnover rate of muscle proteins was related to the physiological function of the muscle in dogs, fowl, rats, and mice. The turnover rates of mixed muscle proteins were most rapid in cardiac muscle, intermediate in red tonic and mixed fiber-type muscles, and slowest in white twitch skeletal muscle. This same progression in turnover rates also was shown in the subcellular fractions of muscle-sarcoplasmic and myofibrillar proteins-as well as in purified proteins, myosin, and tropomyosin. The RNA concentration of muscle was highly correlated with the protein turnover rate, and the RNA activity, i.e., the translational efficiency of the RNA, was similar in the different muscle types.