Free and Protein-Bound Lysine Flux in Developing Rabbit Brain

The rate of flux of lysine from plasma to the nonprotein nitrogen fraction of brain and the rate of flux of lysine from the nonprotein nitrogen fraction to brain proteins is greater in newborn rabbits than in rabbits 12 days old. These in vivo findings parallel the in vitro findings of other investigators that cerebral tissue in the newborn has greater ability to incorporate amino acids into brain protein than cerebral tissue removed from slightly older animals. The greater rate of flux of lysine into protein of the more immature brain most likely is a reflection of the dominance of the synthesis of rapidly metabolized brain proteins at this age.