Ontogeny of Membrane-Bound Protein Phosphorylating Systems in the Rat

Abstract

The ontogeny of the major intrinsic phosphoproteins in membrane fractions prepared from cerebral cortex was studied in the rat. The apparent membrane content of 4 phosphoproteins increased markedly over the period 10-15 days after birth, i.e. coinciding with the onset of synaptogenesis. Two of these proteins (molecular weights 79,000 and 86,000) were phosphorylated in cyclic AMP-dependent reactions, and two (molecular weights 50,000 and 162,000) were phosphorylated in reactions dependent on Ca2+ + cytosol extract. The apparent content of other acceptor proteins phosphorylated in analogous reactions increased more gradually from birth to adulthood. In contrast the apparent membrane content of a protein of 47,000 daltons, which was phosphorylated in a reaction requiring Ca2+ only, was relatively very high at birth and until 15 days of age, but then declined 6-fold until adulthood was reached. The relative distribution of the intrinsic phosphoproteins in several particulate fractions was also compared in 1- and 19-day-old rats. In 1-day-old animals the phosphoprotein of 47,000 daltons was found predominantly in a light membrane fraction, but at 19 days it was only just discernible in the equivalent fraction and was found instead in heavier fractions.