Evolution de quelques enzymes du métabolisme énergétique au cours du développement embryonnaire et post-natal des muscles squelettiques du rat

Abstract

Summary We have studied through the late embryonic and early postnatal period of rat skeletal muscle development, the evolution of four characteristic enzymes : glycogen phosphorylase ( a and b forms), phosphorylase kinase, UDPG glycogen synthetase (I and D forms) and phosphocreatine kinase. The activity of UDPG glycogen synthetase increases before that of the other three enzymes. Its specific activity rises in two steps : a first increase is observed from the 17th to the 19th day of embryonic development reaching a level which stays constant until after birth followed by a second increase during the early postnatal period. Phosphocreatine kinase activity increases progressively during the entire pre and postnatal period. The increase in specific activity of phosphorylase and phosphorylase kinase is also progressive ; however their rate of increase is greater after birth. The ratio of the specific activity of these two enzymes remains constant during the developmental period studied. This result could indicate that their synthesis might be coordinated. The proportion of phosphorylase present in form a decreases after birth, while the proportion of glycogen synthetase present in form I increases. These variations coincide with a decrease in glycogen concentration, suggesting a possible control by glycogen at the level of phosphorylation on these two enzymes.