Metabolic Studies on ¹²⁵i‐labelled Beta‐trace Protein, With Special Reference to Synthesis Within the Central Nervous System

By means of single radial immunodiffusion on agar, the concentration of beta‐trace protein in serum was estimated to about 0.4 mg per 100 ml, i.e. seven times lower than the concentration in CSF. The turnover time in serum was found to be about 1.2 h and the daily amount of beta‐trace protein metabolized was approx. 240 mg. The turnover time in CSF was about 3 h after injection of 125 I‐labelled beta‐trace protein into the lumbar spinal space. The data suggest a synthesis of beta‐trace protein within the CNS of about 30 mg daily, i.e. one‐eighth of the intravascularly metabolized beta‐trace protein.