The development of enzymes of phosphocreatine biosynthesis in the rat

Abstract The development of creatine kinase of skeletal muscles of fore legs, hind legs, heart, and brain of the rat has been studied. The activity of this enzyme of skeletal muscles of the fore legs was found to increase with age in a biphasic manner: a 7-fold increase was observed in the period 5–10 days after birth followed by a 3-fold increase in the period 15–20 days after birth. The development of enzymes involved in creatine biosynthesis has also been studied. The activity of glycine transaminidase of kidney cortex was found to be low in fetal life and increased about 10 times in the 30-day period after birth. The activity of guanidinoacetate transmethylase was high in fetal rat liver and decreased around birth to the adult level. The results indicate that the fetal rat has the capacity for the biosynthesis of creatine.