Separate Turnover of Cytochrome C and Myoglobin in the Red Types of Skeletal Muscle

The purpose of this investigation was to determine whether cytochrome c and myoglobin have similar turnover rates in the three types of skeletal muscles. Exercise (endurance training) was used as an inducing stimulus to increase their concentrations. The half-lives (t 1/2) were subsequently estimated from the time course of return to base-line levels after cessation of exercise. When exercise was stopped, cytochrome c concentration returned rapidly to control levels; the lengths of t 1/2 were approximately 8 days in fast-twitch red, 5 days in slow-twitch red, and 9 days in mixed muscles. These findings confirm previous results of cytochrome c turnover. The concentration of myoglobin decreased at a slower rate than that observed for cytochrome c during detraining in fast-red slow-red, and plantaris muscles, and did not return to sedentary control levels throughout the 50-day detraining period. Myoglobin concentration in fast-twitch white muscle did not increase with the training. These results provide evidence that the degradation rate of myoglobin differs from that of cytochrome c in the red types of skeletal muscle. These elevated myoglobin levels may, in part, provide one explanation for the slow rate of decline in aerobic power that has been observed when individuals stop exercising.