Abstract
When mice were fed on a high protein diet (70% casein), there were increases in the levels of ornithine, urea and arginase activity. Inorganic ammonia, however, kept almost constant level regardless of protein content of the diet. Ornithine-keto acid transaminase (OKT) reacted with α-ketoglutarate formed by the TCA cycle to produce glutamate and glutamic semialdehyde by the addition of ornithine to isolated mitochondria. In this system glutamic semialdehyde was further oxidized to glutamate. The OKT-TCA cycle reaction was inhibited by valine which is a competitive inhibitor of OKT to ornithine, and by ammonia which inhibits the supply of α-ketoglutarate. Hepatic ornithine content was elevated by the injection of ornithine, valine or both.
