Effects of various conditions on the movement of carbon atoms derived from glucose into and out of protein in rat brain

The time course of entry of radioactive carbon from intravenously administered [U-14C]-glucose into protein in five brain regions in rats was studied using an automatic amino acid analyzer coupled, through a flow cell, with a scintillation counter. Radioactivity appeared in protein-bound alanine and in glutamic and aspartic acids and, more slowly and to a much lesser extent, in serine, proline, and glycine; none was detected in any other bound amino acids. There appear to be two main groups of proteins, one of which turns over more slowly than the other. In pentobarbital narcosis, radioactivity in protein-bound alanine increased but no other changes were obvious. In convulsions induced by pentylenetetrazol or picrotoxin, and during hypoxia, the entry of radioactive carbon into protein-bound alanine, glutamic acid, and aspartic acid decreased. At 24 h after the injection of radioactive glucose, radioactivity in free amino acids had almost completely disappeared in normal animals though protein remained radioactive. Pentobarbital narcosis did not affect this situation. Radioactivity was released from protein into free amino acids during hypoxia, during convulsions induced by pentylenetetrazol, picrotoxin, or oxygen at high pressure, and after insulin treatment. Evidence was obtained that free alanine occurs in more than one pool.