title: Cytochrome c turnover in rat skeletal muscles.
abstract: Exercise induces an increase in cytochrome c concentration in skeletal muscle. This adaptation provides an approach to studying the turnover of cytochrome c that avoids the problem of reutilization encountered with isotopic tracers. The half-life of cytochrome c was estimated from the time course of the increase in its concentration to a new, higher, steady state level in response to exercise training, and from the decrease in cytochrome c after cessation of exercise. The half-time of the increase in cytochrome c concentration was approximately 6 days, while the half-time of the decrease was 7 to 8 days in the fast red and slow red types of muscle. The finding that the half-times of the increase and of the decrease in cytochrome c concentration are similar provides evidence that the exercise-induced increase in cytochrome c is due to an increase in its rate of synthesis. These half-times are much shorter than those obtained with isotopic tracers. It had been thought that the heme precursor delta-aminolevulinate is not reutilized. However, the half-time of the decrease in radioactivity of cytochrome c labeled with delta-aminol[14C]levulinate was 45 days, and increased to 60 days in response to exercise, in fast red muscle. The half-time of the decrease in radioactivity of cytochrome c labeled with [(3H)]leucine in gastrocnemius muscle was shorter than with delta-amino[14C]levulinate (18 days compared to 38 days). These results indicate that when delta-amino(14C)levulinate is used to label heme, reutilization is a serious problem in skeletal muscle.
mesh_terms: D000622:Aminolevulinic Acid / Q000378:metabolism; D000818:Animals; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003574:Cytochrome c Group / Q000096:biosynthesis / Q000378:metabolism*; D005260:Female; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D005082:Physical Exertion; D051381:Rats; D013466:Sulfurtransferases / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D000622:Aminolevulinic Acid; D002950:Citrate (si)-Synthase; D013466:Sulfurtransferases