Biochemical studies of chick brain development and maturation: II. Alterations in the mechanisms of cell-free protein synthesis.

The molecular mechanisms responsible for the decreased cell-free protein synthetic activity of chicken brain (cerebrum, cerebellum, and optic lobes) from the late embryonic stage to the adult stage were investigated. The changes in polyribosome content closely paralleled changes in cell-free protein synthetic activity; both increased during late embryonic development, reached a maximum around hatching,and thereafter decreased to the level found in the adult. Both cell sap and microsomal or ribosomal fractions from the adult brain tissue were less active in protein synthesis; however, the microsomal or ribosomal fractions contributed more to the decreased protein synthesis than did the cell sap. The lower activity of adult cell sap in protein synthesis was primarily due to a decreased activity in the aminoacylation of tRNA with no apparent change in the ability of the cell sap to catalyze the elongation of polyphenylalanine synthesis. Ribosomal particles (80 S) from adult and embryonic brain tissue had similar biological activities and fidelity in the translation of polyuridylic acid; however, the cell-free protein synthetic activity of the embryonic post-mitochondrial supernatant preparation was more sensitive to inhibitors of the initiation of protein synthesis (aurintricarboxylic acid and polyinosinic acid) than adult post-mitochondrial supernatant, indicating a decreased initiation capacity in adult brain post-mitochondrial supernatant compared to embryonic brain post-mitochondrial supernatant.