Repression of an Acetylornithine Permeation System.

plete mixture of amino acids resulted in a large suppression of the incorporation. The reason for this effect is also unknown. It may be caused by an imbalance of amino acids since, in a cell-free preparation from E. coli, a balanced mixture of amino acids that reflect the composition of E. coli protein is superior to an equimolar mixture of amino acids. Summary.-A system from developing maize endosperm consisting of washed particles plus a pH 5.2 fraction from the supernatant that actively incorporates leucine-C4 -into protein is described. The system requires a source of energy and GTP. The incorporation is inhibited by treatment with ribonuclease or chloramphenicol. When operating optimally, the incorparationefficiency is 1 to 2 per cent of the added isotope making this system comparable to the mammalian systems.