The turnover of protein in discrete areas of rat brain.

1. Rats were injected serially with [(14)C]glucose to obtain a constant specific radioactivity of brain amino acids. Measurements with this system for periods of up to 8h gave an apparent mean half-life for protein in whole brain of 85h (indicating the presence of a protein fraction with much more rapid turnover than this). 2. The half-lives of proteins in the granule-cell, molecular and white-matter layers of cerebellum were also determined. These had values of 33, 59 and 136h respectively. In addition, the incorporation into protein in six layers of the cerebral cortex, subjacent white matter and five layers of Ammon's horn was studied. All cell-body layers incorporated amino acids at about the same rate irrespective of location, and these rates were considerably higher than those for incorporation into proteins in areas rich in dendrites or fibre tracts. 3. A new method for measuring small amounts of glutamate with a cyclic enzyme system is presented.